In order to calculate the multipoles in real materials with considerable intersite Coulomb interaction V,we develop a self-consistent program which starts from the frst-principles calculations to solve the tight-bindi...In order to calculate the multipoles in real materials with considerable intersite Coulomb interaction V,we develop a self-consistent program which starts from the frst-principles calculations to solve the tight-binding Hamiltonian including onsite Coulomb repulsion U,V,and spin-orbital couplingλ.The program is applied to Ba_(2)MgReO_(6)to fgure out the mechanism of structural instability and magnetic ordering.A comprehensive quadrupole phase diagram versus U and V withλ=0.28 eV is calculated.Our results demonstrate that the easy-plane anisotropy and the intersite Coulomb repulsion V must be considered to remove the orbital frustration.The increase of V to>20 meV would arrange quadrupole Q_(x^(2)-y^(2))antiparallelly,accompanied by small parallel Q_(3z)^(2)-r^(2),and stabilize Ba_(2)MgReO_(6)into the body-centered tetragonal structure.Such antiparallel Q_(x^(2)-y^(2))provides a new mechanism for the Dzyaloshinskii-Moriya interaction and gives rise to the canted antiferromagnetic(CAF)state along the[110]axis.Moreover,sizable octupoles such as O_(21)^(31),O_(21)^(33),O_(21)^(34)and O_(21)^(36)are discovered for the frst time in the CAF state.Our study not only provides a comprehensive understanding of the experimental results in Ba_(2)MgReO_(6),but also serves as a general and useful tool for the study of multipole physics in 5d compounds.展开更多
The ground-state magnetic ordering of uranium mononitride(UN)remains a contentious topic due to the unexpected lack of crystallographic distortion in the traditionally accepted 1k antiferromagnetic(AFM)state.This disc...The ground-state magnetic ordering of uranium mononitride(UN)remains a contentious topic due to the unexpected lack of crystallographic distortion in the traditionally accepted 1k antiferromagnetic(AFM)state.This discrepancy casts doubt on the validity of the 1k magnetic ordering of UN.Here,we investigate the crystal structure,high-pressure phase transitions,and dynamical and mechanical properties of UN in its 1k and 3k AFM ground states using density functional theory(DFT).Our results reveal that the undistorted 3k AFM state of Fm3m within the DFT+U+SOC scheme is more consistent with experimental results.The Hubbard U and spin-orbit coupling(SOC)are critical for accurately capturing the crystal structure,high-pressure structural phase transition,and dynamical properties of UN.In addition,we have identified a new high-pressure magnetic phase transition from the nonmagnetic(NM)phase of R3m to the P63/mmc AFM state.Electronic structure analysis reveals that the magnetic ordering in the ground state is primarily linked to variations in partial 5f orbital distributions.Our calculations provide valuable theoretical insights into the complex magnetic structures of a typical strongly correlated uranium-based compound.Moreover,they provide a framework for understanding other similar actinide systems.展开更多
The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1...The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3（x = 0,0.02,0.05,0.10,and 0.20） single crystals in the basal MnO2 plane.The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion,which makes the nearest neighboring（NN） FM interaction dominant over the next nearest neighbor（NNN） AFM interaction.This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering,which collapses when x ≥ 0.05.The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.展开更多
Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzer...Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzero temperature according to the Mermin-Wagner theorem.By use of the spin Green's function method,we calculated the magnetizations of Heisenberg nanoribbons decorated by side spins with single-ion anisotropy and found that the system exhibits a nonzero transition temperature,whether the decorated edge spins of the system link together or separate from each other.When the width of the nanoribbon achieves infinite limit,the transition temperatures of the system tend to the same finite constant eventually whether one edge or both edges are decorated by side spins in the nanoribbon.The results reveal that the magnetism of a low-dimensional spin system is different from that of a threedimensional spin system.When the single-ion anisotropy of edge spins in a Heisenberg spin nanoribbon can be modulated by an electric field experimentally,various useful long-range magnetic orders of the system can be obtained.This work can provide a detailed theoretical basis for designing and fabricating next-generation low-dimensional magnetic random-access memory.展开更多
The magnetism of highly oriented pyrolytic graphite （HOPG） induced by ion implantation is investigated with electron spin resonance （ESR） spectroscopy and magnetization measurements. The results indicate that the ...The magnetism of highly oriented pyrolytic graphite （HOPG） induced by ion implantation is investigated with electron spin resonance （ESR） spectroscopy and magnetization measurements. The results indicate that the ESR spectra of the HOPG sample correlate with ion species, incident energy and dose of implantation. The correlation of the ESR spectra and magnetism of the HOPG sample with ：2C＋ ion implantation and H＋ ion implantation are studied in detail. The ferromagnetism of the HOPG sample is likely related to the asymmetric L1 line, which may be attributed to the interaction between localized defects and itinerant electrons occupied in the ＇impurity＇ band induced by ion implantation.展开更多
Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(...Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(MD) effect in Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) poly crystalline samples,which possess a non-centrosymmetric polar structure with space group Pna2_(1).In Ho_(2)Cu_(2)O_(5),Ho^(3+) and Cu^(2+) sublattices order simultaneously,exhibiting a typical paramagnetic to antiferromagnetic transition at 13.1 K.While for Yb_(2)Cu_(2)O_(5),two magnetic transitions which originate from the orderings of Yb^(3+)(7.8 K) and Cu^(2+)(13.5 K) sublattices are observed.A magnetic field induced metamagnetic transition is obtained in these two cuprates below Neel temperature(T_(N)).By means of dielectric measurement,distinct MD effect is demonstrated by the dielectric anomaly at T_(N.)Meanwhile,the MD effect is found to be directly related to the metamagnetic transition.Due to the specific spin configuration and different spin evolution in the magnetic field,a positive MD effect is formed in Ho_(2)Cu_(2)O_(5),and a negative one is observed in Yb_(2)Cu_(2)O_(5).The spontaneous dielectric anomaly at T_(N) is regarded as arising from the shifts in optical phonon frequencies,and the magnetoelectric coupling is used to interpret the magnetic field induced MD effect.Moreover,an H-T phase diagram is constructed for Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) based on the results of isothermal magnetic and dielectric hysteresis loops.展开更多
Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-...Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-troscopy and standard strain gauge techniques. The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration, deviating from the Vegard's law. Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0. The saturation magnetization Ms at temperatures 1.5 K, 77 K and 300 K have the same variation tendency as the composition dependence of Curie temperature, in consistence with rigid-band model. The easy magnetization direction (EMD) of Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x<0.6, and changes to [110] for x=0.8, while Sm0.9Pr0.1Co2 stays in the paramagnetic state at room temperature. The composition dependence of the average hyperfine field,Hhf , demonstrates a similar variation tendency as that of the saturation magnetization Ms and Curie temperature Tc. The spontaneous magnetostricton Am increases with increasing Co content. The saturation magnetostriction λs decreases monotonically with increasing x, which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of Am. A two-sublattice model has been proposed to understand the intermediate region between the [111] and [110] spin configurations, which can also be used to explain the temperature dependence of magnetization.展开更多
We report here a new class of ammonium metal-formate frameworks of[NH_(2)NH_(3)][M(HCOO)_(3)](M=Mn^(2+),Zn^(2+),Co^(2+)and Mg^(2+))incorporating hydrazinium as the cationic template and component.The perovskite Mn and...We report here a new class of ammonium metal-formate frameworks of[NH_(2)NH_(3)][M(HCOO)_(3)](M=Mn^(2+),Zn^(2+),Co^(2+)and Mg^(2+))incorporating hydrazinium as the cationic template and component.The perovskite Mn and Zn members possess anionic 4^(12)·6^(3)metal-formate frameworks with cubic cavities occupied by the NH_(2)NH_(3)^(+)cations,while the Co and Mg members have chiral 49·66 metal-formate frameworks,with chiral hexagonal channels accommodating NH_(2)NH_(3)+cations.On heating,the Mn and Zn members undergo phase transitions around 350 K.The structures change from low temperature(LT)polar phases in Pna2_(1)to high temperature(HT)non-polar phases in Pnma,due to the thermally activated librational movement of the NH_(2)end of the NH_(2)NH_(3)^(+)in the cavity and significant framework regulation.The Co and Mg members in LT belong to non-polar P2_(1)2_(1)2_(1),are probably antiferroelectric,and they show phase transitions at 380 K(Co)and 348 K(Mg),and the structures change to polar HT phases in P6_(3),triggered by the order-disorder transition of the cation from one unique orientation in LT to three of trigonally-disorder state in HT.Accompanying the phase transitions,which are ferro-to para-electric for Mn and Zn members while antiferro-to ferro-electric for Co and Mg,prominent anisotropic thermal expansions including negative ones,and dielectric anomalies,are observed.The spontaneous polarization values are estimated at 3.58(Mn,110 K),3.48(Zn,110 K),2.61(Co,405 K)and 3.44(Mg,400 K)μC cm^(-2),respectively,based on the positive and negative charge separations in the polar structures.The structure-property relevance is established based on the order-disorder transitions of NH2NH3+and the conformity and adaptability of the metal-formate frameworks to match such order-disorder alternations.The Mn and Co members show spin-canted antiferromagnetic long-range-ordering,with Néel temperatures of 7.9 K and 13.9 K,respectively.Therefore,the two members show coexistence of electric and magnetic orderings in the low temperature region,and they are possible molecule-based multiferroics.展开更多
Host–vip interactions between the aromatic molecules benzene,toluene,aniline and nitrobenzene and the redox-active TCNQ-based metal–organic framework(MOF),Fe(TCNQ)(4,4’-bpy)(1)(TCNQ=7,7,8,8-tetracyanoquinodimetha...Host–vip interactions between the aromatic molecules benzene,toluene,aniline and nitrobenzene and the redox-active TCNQ-based metal–organic framework(MOF),Fe(TCNQ)(4,4’-bpy)(1)(TCNQ=7,7,8,8-tetracyanoquinodimethane),have been found to modulate spontaneous magnetization behaviours at low temperatures.An analogous MOF,Mn(TCNQ)(4,4’-bpy)(2)with isotropic Mn(II)ions as well as the two-dimensional compound Fe(TCNQ)(DMF)_(2)·2DMF(3·2DMF),were also prepared as models for studying the effects of single-ion magnetic anisotropy and structural distortion on spin canting.The results indicate vip-dependent long range magnetic ordering occurs at low temperatures,which correlates with the electrostatic and steric effects of the incorporated aromatic vips.展开更多
Precise electric control of magnetic order and anomalous Hall conductivity(AHC)is pivotal for spintronics.While electric-field control of magnetic order and AHC has been explored in magnetoelectric materials,achieving...Precise electric control of magnetic order and anomalous Hall conductivity(AHC)is pivotal for spintronics.While electric-field control of magnetic order and AHC has been explored in magnetoelectric materials,achieving precise and energy-efficient magnetic order switching between two P^(^)T^(^)symmetry-connected magnetic states remains challenging.Here,we propose the utilization of the combined P^(^)T^(^)symmetry that establishes a direct connection between electric polarization and magnetic orders,to electrically manipulate magnetic order and the AHC.Using 3MnB_(2)T_(4)·2B_(2)T_(3)(B=Sb/Bi,T=Se/Te)as an example,we demonstrate that the P^(^)T^(^)connected up-up-down(UUD)and up-down-down(UDD)states exhibit switchable magnetic configurations via electric polarization.The energy difference between the UUD and UDD states is linearly modulated by electric polarizations,enabling full control of the magnetic states via electric field,spontaneous polarization,or even weak sliding ferroelectricity.The findings demonstrate that P^(^)T^(^) symmetry can be well utilized to design electric polarization-controlled magnetic orders and will find important applications in spintronics.展开更多
Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer...Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer,strong magnetic responses were observed in the magnetic force microscopy (MFM) measurement,which revealed that the films were independent of dopant particles and clusters. Numerical simulation on the data of atomic force microscope (AFM) and MFM measurements covering the whole microstructure validated the formation of long range magnetic order. This result excluded a variety of controversial origins of room-temperature ferromagnetism in the GaN: Mn and gave a strong evidence of our GaN: Mn as the intrinsic diluted magnetic semiconductor (DMS). The forwarded method for accurate characterization of long range magnetic order could be applied to a wide range of DMS and diluted magnetic oxide (DMO) systems.展开更多
The alloying and magnetic disordering effects on site occupation,elastic property,and phase stability of Co_(2)Y Ga(Y=Cr,V,and Ni)shape memory alloys are systematically investigated using the first-principles exact mu...The alloying and magnetic disordering effects on site occupation,elastic property,and phase stability of Co_(2)Y Ga(Y=Cr,V,and Ni)shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method.It is shown that with the increasing magnetic disordering degree y,their tetragonal shear elastic constant C′(i.e.,(C_(11)-C_(12))/2)of the L2_(1) phase decreases whereas the elastic anisotropy A increases,and upon tetragonal distortions the cubic phase gets more and more unstable.Co_(2)Cr Ga and Co_(2)VGa alloys with y≥0.2 thus can show the martensitic transformation(MT)from L2_(1)to D0_(22)as well as Co_(2)Ni Ga.In off-stoichiometric alloys,the site preference is controlled by both the alloying and magnetic effects.At the ferromagnetism state,the excessive Ga atoms always tend to take the Y sublattices,whereas the excessive Co atom favor the Y sites when Y=Cr,and the excessive Y atoms prefer the Co sites when Y=Ni.The Ga-deficient Y=V alloys can also occur the MT at the ferromagnetism state by means of Co or V doping,and the MT temperature TMshould increase with their addition.In the corresponding ferromagnetism Y=Cr alloys,nevertheless,with Co or Cr substituting for Ga,the reentrant MT(RMT)from D0_(22)to L2_(1)is promoted and then TMfor the RMT should decrease.The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state.At the ferromagnetism state,it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as Y and Ga.展开更多
Na_(4-δ)Ni Te O_(6) is a rare example in the transition-metal tellurate family of realizing an S=1 spin-chain structure.By performing neutron powder diffraction measurements,the ground-state magnetic structure of Na_...Na_(4-δ)Ni Te O_(6) is a rare example in the transition-metal tellurate family of realizing an S=1 spin-chain structure.By performing neutron powder diffraction measurements,the ground-state magnetic structure of Na_(4-δ)Ni Te O_(6) is determined.These measurements reveal that below T_N~6.8(2)K,the Ni^(2+) moments form a screwed ferromagnetic(FM)spin-chain structure running along the crystallographic a axis but these FM spin chains are coupled antiferromagnetically along the b and c directions,giving rise to a magnetic propagation vector of k=(0,1/2,1/2).This zigzag magnetic order is well supported by first-principles calculations.The moment size of Ni^(2+) spins is determined to be 2.1(1) μ_(B) at 3 K,suggesting a significant quenching of the orbital moment due to the crystalline electric field(CEF)effect.The previously reported metamagnetic transition near H_(c)~0.1 T can be understood as a field-induced spin-flip transition.The relatively easy tunability of the dimensionality of its magnetism by external parameters makes Na_(4-δ)Ni Te O_(6)a promising candidate for further exploring various types of novel spin-chain physics.展开更多
Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds.Here,we report two metal-organic frameworks[Co^Ⅱ(ox)(bphy)·0.1(DMF)·0.1(Me OH)]n(1)and[Co3^Ⅱ(ox)3(...Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds.Here,we report two metal-organic frameworks[Co^Ⅱ(ox)(bphy)·0.1(DMF)·0.1(Me OH)]n(1)and[Co3^Ⅱ(ox)3(bphy)2(DMF)2]n(2)comprised of zigzag and necklace Co^Ⅱ-ladders,respectively.Together with a previously reported compound[Co^Ⅱ(ox)(bphy)·0.2(DMF)]n(3)consisting of spiraling zigzag Co^Ⅱ-ladders,these three compounds provide a good system for comparative structural and magnetic studies.Comprehensive magnetic analysis reveals that the three compounds undergo long-range magnetic ordering at^2.6 K but exhibit vastly different short-range magnetic correlations:compound 1 shows short-range spin-canted antiferromagnetism ordering at^14.0 K;compound 2 demonstrates successive short-range antiferromagnetism ordering at^15.5and^12.6 K;compound 3 shows slow magnetic relaxation with Tb≈4.6 K.These results demonstrate long-range magnetic ordering is readily accessible in the frameworks of ox^2-bridging Co^Ⅱ-ladders linked by bphy,where short-range magnetic correlations can be systematicly tuned by the Co^Ⅱ-ladder structures.展开更多
A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMo06 （SFMO）. X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits ...A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMo06 （SFMO）. X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9（2）% from 94.2（3）%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 #s at 300 K, and the one for the traditional sol-gel method sample is 0.946#9. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.展开更多
Altermagnets represent a newly discovered class of magnetically ordered materials.Among all the candidates,CrSb stands out due to its largest spin splitting energy and highest Néel temperature exceeding 700 K,mak...Altermagnets represent a newly discovered class of magnetically ordered materials.Among all the candidates,CrSb stands out due to its largest spin splitting energy and highest Néel temperature exceeding 700 K,making it promising for room-temperature spintronic applications.Here we have successfully grown high quality CrSb(100)thin film on GaAs(110)substrate by molecular beam epitaxy.Using angle-resolved photoemission spectroscopy,we successfully obtained the three-dimensional electronic structure of the thin film.Moreover,we observed the emergence of the altermagnetic splitting bands corresponding to the calculated results along the low symmetry pathsT-QandP-D.The bands near the Fermi level are only spin splitting bands along theP-Ddirection,with splitting energy reaching as high as 910 meV.This finding provides insights into the magnetic properties of CrSb thin films and paves the way for further studies on their electronic structure and potential applications in spintronics.展开更多
FeSe is an Fe-based paramagnetic superconductor with the simplest structure.The competition between the Néel and stripe magnetic orders is believed to be one of the reasons for the absence of magnetic orders in F...FeSe is an Fe-based paramagnetic superconductor with the simplest structure.The competition between the Néel and stripe magnetic orders is believed to be one of the reasons for the absence of magnetic orders in FeSe.FeSe is recognized as a prototypical platform for competing magnetic interactions,including Néel,stripe,and staggered antiferromagnetic coupling.However,the correlations between these magnetic orders and how they change with varying environmental conditions require further study.Here,we calculated the magnetic order of monolayer FeSe in three diferent environments:pure one,with slight lattice distortion,and on SrTiO_(3) substrate,by frst principles calculations.We fnd that in the calculated dispersion relation E(q)between the spin spiral energy E and spin spiral vector q of the monolayer FeSe structure,the stripe magnetic order M(π/2,π/2)has the lowest energy,and there is a fat E(q)between the wave vector X(π/2,0)and Néel magnetic order 2X(π,0),which are the degenerate E(q)states.The ground state of M and the highest density of states around 2X may be the reason for the competition of two magnetic orders.The slight lattice distortion does not alter the magnetic properties of monolayer FeSe.When monolayer FeSe is attached to the SrTiO_(3)substrate,the degenerate E(q)is still retained;meanwhile,the energy of the 2X(π,0)state is closer to the M state,which may be one of the reasons for the increase of superconducting temperature in FeSe/SrTiO_(3).展开更多
Static tensile test and tensile-tensile fatigue test of medium carbon steel sheet specimens with surface crack precut were performed on MTS810 hydraulic testing machine to clear the meaning of the point of Hp(y) value...Static tensile test and tensile-tensile fatigue test of medium carbon steel sheet specimens with surface crack precut were performed on MTS810 hydraulic testing machine to clear the meaning of the point of Hp(y) value zero. Magnetic memory signals were measured during the test process. The results show that only one point of Hp(y) zero value exists in all measured magnetic signal curves during the loading process, which should be a sign of intersection of positive-negative magnetic poles after magnetic ordered state appears and does not indicate the position of surface crack precut. The analysis shows that the surface crack precut can not interrupt the magnetic ordered state occurred during the test completely, hence its Hp(y) value is not zero. However, the crack extending to a penetrated defect at the instant of specimen′s fracture leads to the discontinuance of magnetic ordered state.展开更多
We report the successful synthesis of a new diluted magnetic semiconductor(Ca,Na)(Zn,Mn)2Sb2.Na and Mn are doped into the parent compound CaZn2Sb2,which has the same crystal structure as that of"122"type iro...We report the successful synthesis of a new diluted magnetic semiconductor(Ca,Na)(Zn,Mn)2Sb2.Na and Mn are doped into the parent compound CaZn2Sb2,which has the same crystal structure as that of"122"type iron-based superconductor CaFe2As2.Na substitution for Ca and Mn substitution for Zn introduce carriers and spins,respectively.Doping Mn atoms alone up to 5%does not induce any type of magnetic ordering.When both Na and Mn are co-doped,a ferromagnetic ordering with maximum TC^10 K has been observed.Iso-thermal magnetization shows that the coercive field is up to^245 Oe at 2 K.Below TC,a negative magneto-resistance with MR^12%has also been achieved.展开更多
We study the structure, magnetization, electrical transport properties and heat capacity of the pyrochlore iridates A2Ir2O7（A=Y, Eu, Bi）. It is found that magnetic frustration and long-range magnetic order coexist i...We study the structure, magnetization, electrical transport properties and heat capacity of the pyrochlore iridates A2Ir2O7（A=Y, Eu, Bi）. It is found that magnetic frustration and long-range magnetic order coexist in Y2Ir2O7 and Eu2Ir2O7, while Bi2Ir2O7 shows magnetic frustration or short-range magnetic order without long-range magnetic order. The former two compounds show insulating behavior. However, the latter one shows metallic behavior. The variations of the radius of A-site ion affect the conduction bandwidth, correlation and Ir-Ir exchange energy, which in turn determine transport properties and magnetic properties. We also find that the antiferromagnetic ordering of pyrochlore iridates is weakly frustrated. The all-in/all-out type of anisotropy based on spin-orbit coupling plays a key role in releasing the frustration.展开更多
基金was supported by the National Key Research and Development Program of China(Grant Nos.2024YFA1611200 and 2018YFA0307000)the National Natural Science Foundation of China(Grant Nos.12274154 and 12404182)。
文摘In order to calculate the multipoles in real materials with considerable intersite Coulomb interaction V,we develop a self-consistent program which starts from the frst-principles calculations to solve the tight-binding Hamiltonian including onsite Coulomb repulsion U,V,and spin-orbital couplingλ.The program is applied to Ba_(2)MgReO_(6)to fgure out the mechanism of structural instability and magnetic ordering.A comprehensive quadrupole phase diagram versus U and V withλ=0.28 eV is calculated.Our results demonstrate that the easy-plane anisotropy and the intersite Coulomb repulsion V must be considered to remove the orbital frustration.The increase of V to>20 meV would arrange quadrupole Q_(x^(2)-y^(2))antiparallelly,accompanied by small parallel Q_(3z)^(2)-r^(2),and stabilize Ba_(2)MgReO_(6)into the body-centered tetragonal structure.Such antiparallel Q_(x^(2)-y^(2))provides a new mechanism for the Dzyaloshinskii-Moriya interaction and gives rise to the canted antiferromagnetic(CAF)state along the[110]axis.Moreover,sizable octupoles such as O_(21)^(31),O_(21)^(33),O_(21)^(34)and O_(21)^(36)are discovered for the frst time in the CAF state.Our study not only provides a comprehensive understanding of the experimental results in Ba_(2)MgReO_(6),but also serves as a general and useful tool for the study of multipole physics in 5d compounds.
基金supported by the National Natural Science Foundation of China(Grant Nos.12204482 and U2430211)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(Grant No.2020L0537)the Fundamental Research Program of Shanxi Province(Grant No.202103021224250)the Hainan Provincial Natural Science Foundation of China(Grant No.225MS076).
文摘The ground-state magnetic ordering of uranium mononitride(UN)remains a contentious topic due to the unexpected lack of crystallographic distortion in the traditionally accepted 1k antiferromagnetic(AFM)state.This discrepancy casts doubt on the validity of the 1k magnetic ordering of UN.Here,we investigate the crystal structure,high-pressure phase transitions,and dynamical and mechanical properties of UN in its 1k and 3k AFM ground states using density functional theory(DFT).Our results reveal that the undistorted 3k AFM state of Fm3m within the DFT+U+SOC scheme is more consistent with experimental results.The Hubbard U and spin-orbit coupling(SOC)are critical for accurately capturing the crystal structure,high-pressure structural phase transition,and dynamical properties of UN.In addition,we have identified a new high-pressure magnetic phase transition from the nonmagnetic(NM)phase of R3m to the P63/mmc AFM state.Electronic structure analysis reveals that the magnetic ordering in the ground state is primarily linked to variations in partial 5f orbital distributions.Our calculations provide valuable theoretical insights into the complex magnetic structures of a typical strongly correlated uranium-based compound.Moreover,they provide a framework for understanding other similar actinide systems.
基金Project supported by the National Basic Research Program of China (Grant Nos. 2010CB934202 and 2011CB921801)the National Natural Science Foundation of China (Grant Nos. 11174351,50931006,51021061,and 11034004)
文摘The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3（x = 0,0.02,0.05,0.10,and 0.20） single crystals in the basal MnO2 plane.The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion,which makes the nearest neighboring（NN） FM interaction dominant over the next nearest neighbor（NNN） AFM interaction.This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering,which collapses when x ≥ 0.05.The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.
文摘Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzero temperature according to the Mermin-Wagner theorem.By use of the spin Green's function method,we calculated the magnetizations of Heisenberg nanoribbons decorated by side spins with single-ion anisotropy and found that the system exhibits a nonzero transition temperature,whether the decorated edge spins of the system link together or separate from each other.When the width of the nanoribbon achieves infinite limit,the transition temperatures of the system tend to the same finite constant eventually whether one edge or both edges are decorated by side spins in the nanoribbon.The results reveal that the magnetism of a low-dimensional spin system is different from that of a threedimensional spin system.When the single-ion anisotropy of edge spins in a Heisenberg spin nanoribbon can be modulated by an electric field experimentally,various useful long-range magnetic orders of the system can be obtained.This work can provide a detailed theoretical basis for designing and fabricating next-generation low-dimensional magnetic random-access memory.
基金Supported by the Research Foundation for Young Scientist in Shandong Province under Grant No BS2013CL043
文摘The magnetism of highly oriented pyrolytic graphite （HOPG） induced by ion implantation is investigated with electron spin resonance （ESR） spectroscopy and magnetization measurements. The results indicate that the ESR spectra of the HOPG sample correlate with ion species, incident energy and dose of implantation. The correlation of the ESR spectra and magnetism of the HOPG sample with ：2C＋ ion implantation and H＋ ion implantation are studied in detail. The ferromagnetism of the HOPG sample is likely related to the asymmetric L1 line, which may be attributed to the interaction between localized defects and itinerant electrons occupied in the ＇impurity＇ band induced by ion implantation.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11704091)the Open Project of Guangxi Key Laboratory of Nuclear Physics and Nuclear Technology(Grant No.NLK2021-10)the Open Project of Key Laboratory of Novel Materials for Sensor of Zhejiang Province,China(Grant No.ZJKLNMS2021010)。
文摘Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(MD) effect in Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) poly crystalline samples,which possess a non-centrosymmetric polar structure with space group Pna2_(1).In Ho_(2)Cu_(2)O_(5),Ho^(3+) and Cu^(2+) sublattices order simultaneously,exhibiting a typical paramagnetic to antiferromagnetic transition at 13.1 K.While for Yb_(2)Cu_(2)O_(5),two magnetic transitions which originate from the orderings of Yb^(3+)(7.8 K) and Cu^(2+)(13.5 K) sublattices are observed.A magnetic field induced metamagnetic transition is obtained in these two cuprates below Neel temperature(T_(N)).By means of dielectric measurement,distinct MD effect is demonstrated by the dielectric anomaly at T_(N.)Meanwhile,the MD effect is found to be directly related to the metamagnetic transition.Due to the specific spin configuration and different spin evolution in the magnetic field,a positive MD effect is formed in Ho_(2)Cu_(2)O_(5),and a negative one is observed in Yb_(2)Cu_(2)O_(5).The spontaneous dielectric anomaly at T_(N) is regarded as arising from the shifts in optical phonon frequencies,and the magnetoelectric coupling is used to interpret the magnetic field induced MD effect.Moreover,an H-T phase diagram is constructed for Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) based on the results of isothermal magnetic and dielectric hysteresis loops.
基金This work has been supported by the projects No.59725103 and 59871054 of the National Natural Sciences Foundation of China and by the Science and Technology Commnission of Shenyang and Liaoning.Z.J.Guo as aiso indebted to Prof.A.S.Miarkosyan(Russia)for helpful discussions.
文摘Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-troscopy and standard strain gauge techniques. The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration, deviating from the Vegard's law. Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0. The saturation magnetization Ms at temperatures 1.5 K, 77 K and 300 K have the same variation tendency as the composition dependence of Curie temperature, in consistence with rigid-band model. The easy magnetization direction (EMD) of Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x<0.6, and changes to [110] for x=0.8, while Sm0.9Pr0.1Co2 stays in the paramagnetic state at room temperature. The composition dependence of the average hyperfine field,Hhf , demonstrates a similar variation tendency as that of the saturation magnetization Ms and Curie temperature Tc. The spontaneous magnetostricton Am increases with increasing Co content. The saturation magnetostriction λs decreases monotonically with increasing x, which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of Am. A two-sublattice model has been proposed to understand the intermediate region between the [111] and [110] spin configurations, which can also be used to explain the temperature dependence of magnetization.
基金supported by the NSFC(grants 21171010,21290170,21290171)the National Basic Research Program of China(grant 2009CB929403).
文摘We report here a new class of ammonium metal-formate frameworks of[NH_(2)NH_(3)][M(HCOO)_(3)](M=Mn^(2+),Zn^(2+),Co^(2+)and Mg^(2+))incorporating hydrazinium as the cationic template and component.The perovskite Mn and Zn members possess anionic 4^(12)·6^(3)metal-formate frameworks with cubic cavities occupied by the NH_(2)NH_(3)^(+)cations,while the Co and Mg members have chiral 49·66 metal-formate frameworks,with chiral hexagonal channels accommodating NH_(2)NH_(3)+cations.On heating,the Mn and Zn members undergo phase transitions around 350 K.The structures change from low temperature(LT)polar phases in Pna2_(1)to high temperature(HT)non-polar phases in Pnma,due to the thermally activated librational movement of the NH_(2)end of the NH_(2)NH_(3)^(+)in the cavity and significant framework regulation.The Co and Mg members in LT belong to non-polar P2_(1)2_(1)2_(1),are probably antiferroelectric,and they show phase transitions at 380 K(Co)and 348 K(Mg),and the structures change to polar HT phases in P6_(3),triggered by the order-disorder transition of the cation from one unique orientation in LT to three of trigonally-disorder state in HT.Accompanying the phase transitions,which are ferro-to para-electric for Mn and Zn members while antiferro-to ferro-electric for Co and Mg,prominent anisotropic thermal expansions including negative ones,and dielectric anomalies,are observed.The spontaneous polarization values are estimated at 3.58(Mn,110 K),3.48(Zn,110 K),2.61(Co,405 K)and 3.44(Mg,400 K)μC cm^(-2),respectively,based on the positive and negative charge separations in the polar structures.The structure-property relevance is established based on the order-disorder transitions of NH2NH3+and the conformity and adaptability of the metal-formate frameworks to match such order-disorder alternations.The Mn and Co members show spin-canted antiferromagnetic long-range-ordering,with Néel temperatures of 7.9 K and 13.9 K,respectively.Therefore,the two members show coexistence of electric and magnetic orderings in the low temperature region,and they are possible molecule-based multiferroics.
基金supported by the U.S.Department of Energy,Office of Basic Energy Sciences,Division of Materials Sciences and Engineering under Award DE-SC0012582.MFBR thanks Secretaria de Ciencia y Tecnologia del Distrito Federal(SECITI).The authors thank Dr John Bacsa for his helpful discussions and Mr Toby Woods for collecting some of the X-ray diffraction data.This research used resources of the Advanced Photon Source,a U.S.Department of Energy(DOE)Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No.DE-AC02-06CH11357ChemMatCARS Sector 15 is supported by the National Science Foundation under grant number NSF/CHE-1346572.
文摘Host–vip interactions between the aromatic molecules benzene,toluene,aniline and nitrobenzene and the redox-active TCNQ-based metal–organic framework(MOF),Fe(TCNQ)(4,4’-bpy)(1)(TCNQ=7,7,8,8-tetracyanoquinodimethane),have been found to modulate spontaneous magnetization behaviours at low temperatures.An analogous MOF,Mn(TCNQ)(4,4’-bpy)(2)with isotropic Mn(II)ions as well as the two-dimensional compound Fe(TCNQ)(DMF)_(2)·2DMF(3·2DMF),were also prepared as models for studying the effects of single-ion magnetic anisotropy and structural distortion on spin canting.The results indicate vip-dependent long range magnetic ordering occurs at low temperatures,which correlates with the electrostatic and steric effects of the incorporated aromatic vips.
基金supported by the Natural Science Basic Research Program of Shaanxi (Program No. 2024JC-YBMS-009)the project of the National Natural Science Foundation of China (Program No. 12474061)+2 种基金Shaanxi Qinchuangyuan High-Level Innovative and Entrepreneurial Talent Introduction Program (QCYRCXM-2023-077)The Natural Science Fund of Shaanxi Province for the key project (2021JZ-07)Leading Talents in Scientifc and Technological Innovation Program of Shaanxi Province, and the Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars. T.C. also thanks the support from the Youth Project of “Shanxi High-level Talents Introduction Plan (5113240032)”. T.C. also thanks Prof. Jian Zhou, Prof. Jingsheng CHEN for the helpful discussions.
文摘Precise electric control of magnetic order and anomalous Hall conductivity(AHC)is pivotal for spintronics.While electric-field control of magnetic order and AHC has been explored in magnetoelectric materials,achieving precise and energy-efficient magnetic order switching between two P^(^)T^(^)symmetry-connected magnetic states remains challenging.Here,we propose the utilization of the combined P^(^)T^(^)symmetry that establishes a direct connection between electric polarization and magnetic orders,to electrically manipulate magnetic order and the AHC.Using 3MnB_(2)T_(4)·2B_(2)T_(3)(B=Sb/Bi,T=Se/Te)as an example,we demonstrate that the P^(^)T^(^)connected up-up-down(UUD)and up-down-down(UDD)states exhibit switchable magnetic configurations via electric polarization.The energy difference between the UUD and UDD states is linearly modulated by electric polarizations,enabling full control of the magnetic states via electric field,spontaneous polarization,or even weak sliding ferroelectricity.The findings demonstrate that P^(^)T^(^) symmetry can be well utilized to design electric polarization-controlled magnetic orders and will find important applications in spintronics.
基金supported by the National Natural Science Foundation of China (Grant Nos.60577030,60776041,60876035)the National Key Basic Research Special Foundation of China (Grant Nos.TG2007CB307004,2006CB921607)
文摘Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer,strong magnetic responses were observed in the magnetic force microscopy (MFM) measurement,which revealed that the films were independent of dopant particles and clusters. Numerical simulation on the data of atomic force microscope (AFM) and MFM measurements covering the whole microstructure validated the formation of long range magnetic order. This result excluded a variety of controversial origins of room-temperature ferromagnetism in the GaN: Mn and gave a strong evidence of our GaN: Mn as the intrinsic diluted magnetic semiconductor (DMS). The forwarded method for accurate characterization of long range magnetic order could be applied to a wide range of DMS and diluted magnetic oxide (DMO) systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174269,11674233and 51301176)the China Postdoctoral Science Foundation(Grant Nos.2013M530133 and 2014T70264)the Natural Science Foundation of Liaoning Province,China(Grant Nos.2019-MS-287 and L201602672)。
文摘The alloying and magnetic disordering effects on site occupation,elastic property,and phase stability of Co_(2)Y Ga(Y=Cr,V,and Ni)shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method.It is shown that with the increasing magnetic disordering degree y,their tetragonal shear elastic constant C′(i.e.,(C_(11)-C_(12))/2)of the L2_(1) phase decreases whereas the elastic anisotropy A increases,and upon tetragonal distortions the cubic phase gets more and more unstable.Co_(2)Cr Ga and Co_(2)VGa alloys with y≥0.2 thus can show the martensitic transformation(MT)from L2_(1)to D0_(22)as well as Co_(2)Ni Ga.In off-stoichiometric alloys,the site preference is controlled by both the alloying and magnetic effects.At the ferromagnetism state,the excessive Ga atoms always tend to take the Y sublattices,whereas the excessive Co atom favor the Y sites when Y=Cr,and the excessive Y atoms prefer the Co sites when Y=Ni.The Ga-deficient Y=V alloys can also occur the MT at the ferromagnetism state by means of Co or V doping,and the MT temperature TMshould increase with their addition.In the corresponding ferromagnetism Y=Cr alloys,nevertheless,with Co or Cr substituting for Ga,the reentrant MT(RMT)from D0_(22)to L2_(1)is promoted and then TMfor the RMT should decrease.The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state.At the ferromagnetism state,it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as Y and Ga.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074023,12004020,11834014,11974036,and12074024)Fundamental Research Funds for the Central Universities in China。
文摘Na_(4-δ)Ni Te O_(6) is a rare example in the transition-metal tellurate family of realizing an S=1 spin-chain structure.By performing neutron powder diffraction measurements,the ground-state magnetic structure of Na_(4-δ)Ni Te O_(6) is determined.These measurements reveal that below T_N~6.8(2)K,the Ni^(2+) moments form a screwed ferromagnetic(FM)spin-chain structure running along the crystallographic a axis but these FM spin chains are coupled antiferromagnetically along the b and c directions,giving rise to a magnetic propagation vector of k=(0,1/2,1/2).This zigzag magnetic order is well supported by first-principles calculations.The moment size of Ni^(2+) spins is determined to be 2.1(1) μ_(B) at 3 K,suggesting a significant quenching of the orbital moment due to the crystalline electric field(CEF)effect.The previously reported metamagnetic transition near H_(c)~0.1 T can be understood as a field-induced spin-flip transition.The relatively easy tunability of the dimensionality of its magnetism by external parameters makes Na_(4-δ)Ni Te O_(6)a promising candidate for further exploring various types of novel spin-chain physics.
基金the National Natural Science Foundation of China(21871262,21805257,21901242)the Natural Science Foundation of Fujian Province(2019J01130)the Recruitment Program of Global Youth Experts。
文摘Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds.Here,we report two metal-organic frameworks[Co^Ⅱ(ox)(bphy)·0.1(DMF)·0.1(Me OH)]n(1)and[Co3^Ⅱ(ox)3(bphy)2(DMF)2]n(2)comprised of zigzag and necklace Co^Ⅱ-ladders,respectively.Together with a previously reported compound[Co^Ⅱ(ox)(bphy)·0.2(DMF)]n(3)consisting of spiraling zigzag Co^Ⅱ-ladders,these three compounds provide a good system for comparative structural and magnetic studies.Comprehensive magnetic analysis reveals that the three compounds undergo long-range magnetic ordering at^2.6 K but exhibit vastly different short-range magnetic correlations:compound 1 shows short-range spin-canted antiferromagnetism ordering at^14.0 K;compound 2 demonstrates successive short-range antiferromagnetism ordering at^15.5and^12.6 K;compound 3 shows slow magnetic relaxation with Tb≈4.6 K.These results demonstrate long-range magnetic ordering is readily accessible in the frameworks of ox^2-bridging Co^Ⅱ-ladders linked by bphy,where short-range magnetic correlations can be systematicly tuned by the Co^Ⅱ-ladder structures.
基金Supported by the National Natural Science Foundation of China under Grant No U1304110the Doctoral Science Foundation of Henan Normal University under Grant No 01026500109
文摘A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMo06 （SFMO）. X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9（2）% from 94.2（3）%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 #s at 300 K, and the one for the traditional sol-gel method sample is 0.946#9. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.
基金supported by the National Key R&D Program of China[Grant No.2023YFA1406304(J J)]the National Natural Science Foundation of China[Grant No.12174362(J J)]+2 种基金the Innovation Program for Quantum Science and Technology[Grant No.2021ZD0302803(D L F)]the New Cornerstone Science Foundation(D L F)Beamline 03U of the Shanghai Synchrotron Radiation Facility,which is supported by ME2 project under contract No.11227902 from the National Natural Science Foundation of China。
文摘Altermagnets represent a newly discovered class of magnetically ordered materials.Among all the candidates,CrSb stands out due to its largest spin splitting energy and highest Néel temperature exceeding 700 K,making it promising for room-temperature spintronic applications.Here we have successfully grown high quality CrSb(100)thin film on GaAs(110)substrate by molecular beam epitaxy.Using angle-resolved photoemission spectroscopy,we successfully obtained the three-dimensional electronic structure of the thin film.Moreover,we observed the emergence of the altermagnetic splitting bands corresponding to the calculated results along the low symmetry pathsT-QandP-D.The bands near the Fermi level are only spin splitting bands along theP-Ddirection,with splitting energy reaching as high as 910 meV.This finding provides insights into the magnetic properties of CrSb thin films and paves the way for further studies on their electronic structure and potential applications in spintronics.
基金supported by the National Natural Science Foundation of China(Grant Nos.11204131 and 11974181)。
文摘FeSe is an Fe-based paramagnetic superconductor with the simplest structure.The competition between the Néel and stripe magnetic orders is believed to be one of the reasons for the absence of magnetic orders in FeSe.FeSe is recognized as a prototypical platform for competing magnetic interactions,including Néel,stripe,and staggered antiferromagnetic coupling.However,the correlations between these magnetic orders and how they change with varying environmental conditions require further study.Here,we calculated the magnetic order of monolayer FeSe in three diferent environments:pure one,with slight lattice distortion,and on SrTiO_(3) substrate,by frst principles calculations.We fnd that in the calculated dispersion relation E(q)between the spin spiral energy E and spin spiral vector q of the monolayer FeSe structure,the stripe magnetic order M(π/2,π/2)has the lowest energy,and there is a fat E(q)between the wave vector X(π/2,0)and Néel magnetic order 2X(π,0),which are the degenerate E(q)states.The ground state of M and the highest density of states around 2X may be the reason for the competition of two magnetic orders.The slight lattice distortion does not alter the magnetic properties of monolayer FeSe.When monolayer FeSe is attached to the SrTiO_(3)substrate,the degenerate E(q)is still retained;meanwhile,the energy of the 2X(π,0)state is closer to the M state,which may be one of the reasons for the increase of superconducting temperature in FeSe/SrTiO_(3).
基金This work was financially supported by the National Natural Science Foundation of China (No.50235030, 50505052).
文摘Static tensile test and tensile-tensile fatigue test of medium carbon steel sheet specimens with surface crack precut were performed on MTS810 hydraulic testing machine to clear the meaning of the point of Hp(y) value zero. Magnetic memory signals were measured during the test process. The results show that only one point of Hp(y) zero value exists in all measured magnetic signal curves during the loading process, which should be a sign of intersection of positive-negative magnetic poles after magnetic ordered state appears and does not indicate the position of surface crack precut. The analysis shows that the surface crack precut can not interrupt the magnetic ordered state occurred during the test completely, hence its Hp(y) value is not zero. However, the crack extending to a penetrated defect at the instant of specimen′s fracture leads to the discontinuance of magnetic ordered state.
基金Project supported by the National Key Research&Development Program of China(Grant No.2016YFA0300402)the Fundamental Research Funds for the Central Universities,China。
文摘We report the successful synthesis of a new diluted magnetic semiconductor(Ca,Na)(Zn,Mn)2Sb2.Na and Mn are doped into the parent compound CaZn2Sb2,which has the same crystal structure as that of"122"type iron-based superconductor CaFe2As2.Na substitution for Ca and Mn substitution for Zn introduce carriers and spins,respectively.Doping Mn atoms alone up to 5%does not induce any type of magnetic ordering.When both Na and Mn are co-doped,a ferromagnetic ordering with maximum TC^10 K has been observed.Iso-thermal magnetization shows that the coercive field is up to^245 Oe at 2 K.Below TC,a negative magneto-resistance with MR^12%has also been achieved.
基金Supported by the National Natural Science Foundation of China(11604071)the Natural Science Foundation of the Education Department of Anhui Province(KJ2016SD49)the Natural Science Foundation of Hefei University(16ZR06ZDB,15RC13,14KY15ZR,2016dtr02)
文摘We study the structure, magnetization, electrical transport properties and heat capacity of the pyrochlore iridates A2Ir2O7（A=Y, Eu, Bi）. It is found that magnetic frustration and long-range magnetic order coexist in Y2Ir2O7 and Eu2Ir2O7, while Bi2Ir2O7 shows magnetic frustration or short-range magnetic order without long-range magnetic order. The former two compounds show insulating behavior. However, the latter one shows metallic behavior. The variations of the radius of A-site ion affect the conduction bandwidth, correlation and Ir-Ir exchange energy, which in turn determine transport properties and magnetic properties. We also find that the antiferromagnetic ordering of pyrochlore iridates is weakly frustrated. The all-in/all-out type of anisotropy based on spin-orbit coupling plays a key role in releasing the frustration.
