Realizing ferromagnetic semiconductors with high Curie temperature TC is still a challenge in spintronics.Recent experiments have reported two-dimensional(2D)room temperature ferromagnetic metals,such as monolayer Cr_...Realizing ferromagnetic semiconductors with high Curie temperature TC is still a challenge in spintronics.Recent experiments have reported two-dimensional(2D)room temperature ferromagnetic metals,such as monolayer Cr_(3)Te_(6).In this paper,through density functional theory(DFT)calculations,we propose a method to obtain 2D high TC ferromagnetic semiconductors through element replacement in these ferromagnetic metals.We predict that monolayer(Cr_(4/6),Mo_(2/6))_(3)Te_(6),created via element replacement in monolayer Cr_(3)Te_(6),is a room-temperature ferromagnetic semiconductor exhibiting a band gap of 0.34 eV and a TC of 384 K.Our analysis reveals that the metal-to-semiconductor transition stems from the synergistic interplay of Mo-induced lattice distortion,which resolves band overlap,and the electronic contributions of Mo dopants,which further drive the formation of a distinct band gap.The origin of the high TC is traced to strong superexchange coupling between magnetic ions,analyzed via the superexchange model with DFT and Wannier function calculations.Considering the fast developments in fabrication and manipulation of 2D materials,our theoretical results propose an approach to explore high-temperature ferromagnetic semiconductors derived from experimentally obtained 2D high-temperature ferromagnetic metals through element replacement.展开更多
Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.T...Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.Theoretical studies have shown that pressure,as an external parameter,significantly affects its ferromagnetic properties.In this study,we have performed comprehensive high-pressure neutron powder diffraction(NPD)experiments on FGT up to 5 GPa to investigate the evolution of its structural and magnetic properties with hydrostatic pressure.The NPD data clearly reveal the robustness of the ferromagnetism in FGT,despite of an apparent suppression by hydrostatic pressure.As the pressure increases from 0 to 5 GPa,the Curie temperature is found to decrease monotonically from 225(5)K to 175(5)K,together with a dramatically suppressed ordered moment of Fe,which is well supported by the first-principles calculations.Although no pressure-driven structural phase transition is observed up to 5 GPa,quantitative analysis on the changes of bond lengths and bond angles indicates a significant modification of the exchange interactions,which accounts for the pressure-induced suppression of the ferromagnetism in FGT.展开更多
The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O...The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O_(8)(BNVO),in which the spin correlation was modulated by unusual oxidation state,leading to different magnetic behavior.The BNVO was modified with topochemical reduction(TR)to yield TR-BNVO with partially reduced valance state of Ni^(+)in the two-dimensional NiO_(6)-honeycomb lattice.Accordingly,the antiferromagnetic order is suppressed by the introduction of locally interposed Ni^(+)and oxygen vacancies,resulting in a ferromagnetic ground state with the transition temperature up to 710 K.A positive magnetoresistance(7.5%)was observed in the TR-BNVO at 40 K under 7 T.These findings show that topological reduction is a powerful approach to engineer low-dimensional materials and accelerate the discovery of new quantum magnetism.展开更多
Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with ...Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with systematically tuned atomic structures.We found that all films exhibit ferroelastic domains with four-fold symmetry and the larger domain size(higher elasticity)is always accompanied by stronger ferromagnetism.We performed synchrotron x-ray diffraction studies to investigate the backbone structure of the CoO6 octahedra,and found that both the ferromagnetism and the elasticity are simultaneously enhanced when the in-plane Co–O–Co bond angles are straightened.Therefore the study demonstrates the inextricable correlation between the ferromagnetism and ferroelasticity mediated through the octahedral backbone structure,which may open up new possibilities to develop multifunctional materials.展开更多
Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by postgrowth thermal annealing.Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and ...Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by postgrowth thermal annealing.Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films.Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature.The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals.The results may be useful for room temperature spintronic applications based on group IV semiconductors.展开更多
In this study, B-doped ZnO nanoparticles were synthesized by template-free solvothermal method. X-ray diffraction analysis reveals that B-doped ZnO nanoparti- cles have hexagonal wurtzite structure. Field emission sca...In this study, B-doped ZnO nanoparticles were synthesized by template-free solvothermal method. X-ray diffraction analysis reveals that B-doped ZnO nanoparti- cles have hexagonal wurtzite structure. Field emission scanning electron microscopy observations show that the nanoparticles have a diameter of 50 nm. The room tem- perature ferromagnetism increases monotonically with increasing B concentration to the ZnO nanoparticles and reaches the maximum value of saturation magnetization 0.0178 A.ma.kg-1 for 5 % B-doped ZnO nanoparticles. Moreover, photoluminescence spectra reveal that B doping causes to produce Zn vacancies （Vzn）. Magnetic moment of oxygen atoms nearest to the B-Vzn vacancy pairs can be considered as a source of ferromagnetism for B-doped ZnO nanoparticles.展开更多
This study focuses on the effect of V-doping on the ferromagnetism（FM） of 6H-SiC powder.The X-ray diffraction results indicate that V is inserted into the 6H-SiC lattice.The Raman spectra reveal that with a V concen...This study focuses on the effect of V-doping on the ferromagnetism（FM） of 6H-SiC powder.The X-ray diffraction results indicate that V is inserted into the 6H-SiC lattice.The Raman spectra reveal that with a V concentration of 25 ppm,the crystalline quality and carrier concentration of 6H-SiC are hardly varied.It is found that after the V-doping process,the saturation magnetization（Ms） and the vacancy concentration of 6H-SiC are both increased.From these results,it is deduced that the effect of V might contribute mainly to the increase of vacancy concentration,thus resulting in the increase of Ms of V-doped 6H-SiC.展开更多
Two-dimensional(2 D)few-layerVSe_(2),V_(1-x)Fe_(x)Se_(2) nanosheets have been synthesized by a hightemperature organic solution-phase method. The thickness of VSe_(2) nanosheets can be tuned from 12 to 5 layers by dec...Two-dimensional(2 D)few-layerVSe_(2),V_(1-x)Fe_(x)Se_(2) nanosheets have been synthesized by a hightemperature organic solution-phase method. The thickness of VSe_(2) nanosheets can be tuned from 12 to 5 layers by decreasing the precursor concentrations. The few-layer VSe_(2) nanosheets show the room-temperature ferromagnetism. The coercivity and magnetization reach 0.024 T and 0.036 mA·m^(2)·g^(-1) at room temperature. The chargedensity wave behavior is also confirmed in VSe_(2) by the hysteresis loops and zero-field-cooling curve. V_(1-x)Fe_(x)Se_(2) nanosheets can be obtained by doping Fe(acac)3 in the reaction process. The room-temperature coercivity and magnetization of V_(0.8)Fe_(0.2)Se_(2) nanosheets are 5 times higher than those of the pure VSe_(2) nanosheets without destroying the structures. The enhancement of magnetization is due to the coupling interaction of 3 d orbits between V and Fe atoms. Higher Fe concentration is beneficial to improve the coercivity, which is attributed to the formation of the second phase Fe3 Se4. This simple chemical preparation method can be extended to prepare the other 2 D materials.展开更多
Large-scale flower-shaped Mn doped ZnO nanostructures have been grown on silicon substrates by simple thermal evaporation at atmospheric pressure.The flower-shaped nanostructure makes up of many nanorods,which are roo...Large-scale flower-shaped Mn doped ZnO nanostructures have been grown on silicon substrates by simple thermal evaporation at atmospheric pressure.The flower-shaped nanostructure makes up of many nanorods,which are rooted in one center.Analysis of X-ray diffraction,high-resolution transmission electron microscopy and Raman spectra results reveal that the products are of single phase with wurtzite structure.Elemental mapping results show that no impurity clusters exist in the doped materials.The photoluminescence spectra demonstrate that many oxygen vacancies exist in the doped materials,and the crystal quality is improved and the content of oxygen vacancies is decreased by annealing treatment.The flower-shaped Mn doped ZnO nanostructures exhibit ferromagnetic ordering above room temperature,and its magnetization is decreased by the annealing treatment,which indicates that the magnetic behavior of the doped materials may be related to the interaction between Mn doping and the oxygen vacancies.展开更多
Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane.By combining X-ray absorption near the edge struct...Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane.By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy,Ti^3＋-V O defect complexes（or clusters） have been identified in annealed crystals at a high vacuum.We elucidate that the unpaired 3d electrons in Ti^3＋ ions provide the observed room-temperature ferromagnetism.In addition,excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.展开更多
We perform a first-principles study of electronic structure and magnetism of C-doped zinc-blende ZnO using the full-potential linearized augmented plane wave method. Results show that C-doped zinc-blende ZnO exhibits ...We perform a first-principles study of electronic structure and magnetism of C-doped zinc-blende ZnO using the full-potential linearized augmented plane wave method. Results show that C-doped zinc-blende ZnO exhibits half-metallic ferromagnetism with a stable ferromagnetic ground state. The calculated magnetic moment of the 32-atom supercell containing one C dopant is 2.00 μ B , and the C dopant contributes most. The calculated low formation energy suggests that C-doped zinc-blende ZnO is energetically stable. The hole-mediated double exchange mechanism can be used to explain the ferromagnetism in C-doped zinc-blende ZnO.展开更多
The synthesis and characterization of Fe-doped CuA102 semiconductor were reported. The samples were synthesized by a simple and cost effective spin-on technique from solid state reaction of Cu20 and A1203 on sapphire ...The synthesis and characterization of Fe-doped CuA102 semiconductor were reported. The samples were synthesized by a simple and cost effective spin-on technique from solid state reaction of Cu20 and A1203 on sapphire （001） substrate. Appropriate ethyl-cellulose （EC） and terpineol are useful for the formation of Fe-doped CuA102 films. X-ray diffraction （XRD） revealed the growth of pure delafossite CuA102 phase ruled out elemental metallic Fe clusters in all the Fe incorporated CuA102 films. The existence of ferromagnetism at room temperature is evidenced by well-defined hysteresis loops. Specially, the saturation magnetization （Ms） values at room temperature have been monotonously enhanced with the increase of Fe composition from 1% to 5%.展开更多
Gear-shape CeO2 microstructures have been synthesized via a facile hydrothermal method with Ce（NO3）3-6H20 as the cerium source, NHaHCO3 as both the precipitator and the carbon source, and cetyltrimethyl ammonium bro...Gear-shape CeO2 microstructures have been synthesized via a facile hydrothermal method with Ce（NO3）3-6H20 as the cerium source, NHaHCO3 as both the precipitator and the carbon source, and cetyltrimethyl ammonium bromide （CTAB） as the surfactant. X-ray diffraction （XRD） inferred that the synthesized CeO2 microstructures exhibited a fluorite structure. The band gap （Eg） of CeO2 samples is larger than that of bulk. X-ray photoelectron spectroscopy （XPS） showed that there are plenty or Ce3＋ ions and oxygen vacancies at the surface of CeO2 samples. All the synthesized CeO2 samples exhibited the room temperature ferromagnetism, and the saturation magnetization increases with the increases of lattice parameter and Eg. The room temperature ferromagnetism mechanism of gear-shape CeO2 is mainly attributed to the influence Ce3＋ ions.展开更多
Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the most promising candidates for next-generation low-cost, high-performance and nano-scale spintronic applications such as spin field-effect t...Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the most promising candidates for next-generation low-cost, high-performance and nano-scale spintronic applications such as spin field-effect transistors and quantum computation/communication. However, as one of the 125 important scientific issues raised by Science journal in 2005 that "is it possible to create magnetic semiconductors that work at room temperature?", how to achieve a feasible ferromagnetic semiconductor with high Curie temperature is still a long-standing challenge despite of tremendous efforts have been devoted in this field since 1960s. The recent discovery of 2D ferromagnetic semiconductors Cr2Ge2Te6 and CrI3 has evoked new research interests in 2D intrinsic ferromagnetic semiconductors. But the low Curie temperature (<45 K) of these materials is still badly hindering their industrial applications.展开更多
The magnetic and structural properties of 2% Ni-doped ZnO powers prepared by sol-gel method were studied. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) of the sample do not show ...The magnetic and structural properties of 2% Ni-doped ZnO powers prepared by sol-gel method were studied. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) of the sample do not show existence of any signal of second phase. The X-photoelectron spectroscopy (XPS) of the sample shows the chemical valence of Ni is +2 and the real Ni concentration is 2.19% determined by X-ray fluorescence spectra (XRFS). The magnetic property performed with superconducting quantum interference device (SQUID) shows that the sample exhibits ferromagnetism above room temperature and the Curie temperature (TC) is about 600 K.展开更多
In this paper,a hydrothermal approach is utilized for the first time in integrating graphene oxide(GO),acetic acid(HAc)and nickel foam to prepare hydrogenated graphene(HG).There are two primary aims of this study:one ...In this paper,a hydrothermal approach is utilized for the first time in integrating graphene oxide(GO),acetic acid(HAc)and nickel foam to prepare hydrogenated graphene(HG).There are two primary aims of this study:one is to ascertain the structure of the as-prepared HG,and the other one is to investigate the ferromagnetism of the HG.Under hydrothermal conditions,GO was reduced and hydrogenated by HAc,while the nickel foam served as a catalyst.This work provides a novel and facile route for the synthesis of hydrogenated graphene,which may lead to the application of hydrogenated graphene in spin electronic devices.展开更多
One-dimensional, diluted magnetic semiconductor nanofibers have attracted increasing attention for their unique magnetic properties, large specific surface area, and high porosity. These qualities lead to excellent pe...One-dimensional, diluted magnetic semiconductor nanofibers have attracted increasing attention for their unique magnetic properties, large specific surface area, and high porosity. These qualities lead to excellent performance in magneto-optical devices, magnetic resonance imaging, ferrofluids and magnetic separation. The purpose of this study is to fabricate P-type one dimensional CuAlO2-based diluted magnetic semiconductor nanofibers. First, we fabricated CuAl0.95Co0.05O2 nanofibers with an average diameter of 1 μm with the electrospinning method. The annealed nanofibers were thermally treated at a temperature of 1 100℃ and then shrunk to a diameter of about 650 nm. We used X-ray diffraction measurements and Raman spectra to confirm that the CUAl0.95CO0.05O2 nanofihers had a single impurity free delafossite phase. The X-ray photoelectron spectroscopy analysis indicates that Co was present in the ＋2 oxidation state, resulting in an room temperature ferromagnetism in the CHAl0.95Co0.05O2 fiber. This contrststs with nonmagnetism in pristine CuAlO2 fiber. The coercivity （Hc） value of 65.26 Oe and approximate saturation magnetization （Ms） of 0.012 emu/g demonstrate good evidence of ferromagnetism at room temperature for CuAl0.95Co0.05O2 nanofibers.展开更多
Nanopowders of Znl_x_y_zMnxNiyLizO [（x = 0.04, y = 0, z = 0）, （x = 0.04, y = 0.03, z = 0） and （x = 0.04, y = 0.03, z = 0.03）] have been synthesized by sol-gel precursor route using ethylene diamine tetraacetic a...Nanopowders of Znl_x_y_zMnxNiyLizO [（x = 0.04, y = 0, z = 0）, （x = 0.04, y = 0.03, z = 0） and （x = 0.04, y = 0.03, z = 0.03）] have been synthesized by sol-gel precursor route using ethylene diamine tetraacetic acid （EDTA） as a metal chelating agent. X-ray diffraction analysis confirms the formation of wurtzite hexagonal structure for all the three compositions. Mn2＋ doped ZnO exhibits room temperature ferromagnetism （RTFM）, and it is found that further Ni2＋ doping has decreased Ms because of limit of solid solubility of transition metal in ZnO. But codoping of monovalent Li1＋, further increases the ferromagnetism （FM） value, due to introduction of free carriers compared to the dual doped samples. Photoluminescence （PL） spectra of the system, exhibit near band edge （NBE） emission peak at --464 nm due to the electron transition from interstitials to the valence band. Recombination of conduction electron with hole trapped at oxygen vacancy, leads to prominent defect emission peaks at --482 nm and 532 nm. The evidence of the formation of metaI-EDTA complexes are found from the Fourier transform infrared spectra at 2800-3800 cm-1 with shifting, splitting of the peak and also drastic variations in the intensity.展开更多
We present a first principle study of Cr-doped In2O3 system using density functional theory. The obtained results show that the Cr ion prefers the cation site of the center of trigonally distorted octahedron and conve...We present a first principle study of Cr-doped In2O3 system using density functional theory. The obtained results show that the Cr ion prefers the cation site of the center of trigonally distorted octahedron and converges to high spin-polarized configuration in the ground state. The hybridization between d-states and the donor states is strong, and the spin-split donor impurity-band model is found to be the most favorable mechanism for the ferromagnetism in this system. The good ferromagnetic property of high Curie temperature is discussed in view of the electronic structure analyses.展开更多
First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the to...First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the total magnetic mo- ment mainly originates from the p--d hybridization of Cu-N and Cu-O as well as p--p coupling interaction between N and O at the Fermi level. The Zn34Cu2035N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the （Cu, N）-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.展开更多
基金supported by the National Key R&D Program of China(Grant No.2022YFA1405100)Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-030)+3 种基金the Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08)GS was supported in part by the Innovation Program for Quantum Science and Technology(Grant No.2024ZD03005)the National Natural Science Foundation of China(Grant No.12447101)Chinese Academy of Sciences.
文摘Realizing ferromagnetic semiconductors with high Curie temperature TC is still a challenge in spintronics.Recent experiments have reported two-dimensional(2D)room temperature ferromagnetic metals,such as monolayer Cr_(3)Te_(6).In this paper,through density functional theory(DFT)calculations,we propose a method to obtain 2D high TC ferromagnetic semiconductors through element replacement in these ferromagnetic metals.We predict that monolayer(Cr_(4/6),Mo_(2/6))_(3)Te_(6),created via element replacement in monolayer Cr_(3)Te_(6),is a room-temperature ferromagnetic semiconductor exhibiting a band gap of 0.34 eV and a TC of 384 K.Our analysis reveals that the metal-to-semiconductor transition stems from the synergistic interplay of Mo-induced lattice distortion,which resolves band overlap,and the electronic contributions of Mo dopants,which further drive the formation of a distinct band gap.The origin of the high TC is traced to strong superexchange coupling between magnetic ions,analyzed via the superexchange model with DFT and Wannier function calculations.Considering the fast developments in fabrication and manipulation of 2D materials,our theoretical results propose an approach to explore high-temperature ferromagnetic semiconductors derived from experimentally obtained 2D high-temperature ferromagnetic metals through element replacement.
基金Project supported by the National Natural Science Foundation of China(Grant No.12074023)the Large Scientific Facility Open Subject of Songshan Lake(Grant No.KFKT2022B05)+1 种基金the Fundamental Research Funds for the Central Universities in ChinaNeutron diffraction experiments at the Materials and Life Science Experimental Facility of the J-PARC were performed through the user program(Proposal No.2023A0185).
文摘Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.Theoretical studies have shown that pressure,as an external parameter,significantly affects its ferromagnetic properties.In this study,we have performed comprehensive high-pressure neutron powder diffraction(NPD)experiments on FGT up to 5 GPa to investigate the evolution of its structural and magnetic properties with hydrostatic pressure.The NPD data clearly reveal the robustness of the ferromagnetism in FGT,despite of an apparent suppression by hydrostatic pressure.As the pressure increases from 0 to 5 GPa,the Curie temperature is found to decrease monotonically from 225(5)K to 175(5)K,together with a dramatically suppressed ordered moment of Fe,which is well supported by the first-principles calculations.Although no pressure-driven structural phase transition is observed up to 5 GPa,quantitative analysis on the changes of bond lengths and bond angles indicates a significant modification of the exchange interactions,which accounts for the pressure-induced suppression of the ferromagnetism in FGT.
基金financially supported by the National Natural Science Foundation of China(NSFC,Nos.21875287,22090041)the Guangdong Basic and Applied Basic Research Foundation(No.2022B1515120014)。
文摘The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O_(8)(BNVO),in which the spin correlation was modulated by unusual oxidation state,leading to different magnetic behavior.The BNVO was modified with topochemical reduction(TR)to yield TR-BNVO with partially reduced valance state of Ni^(+)in the two-dimensional NiO_(6)-honeycomb lattice.Accordingly,the antiferromagnetic order is suppressed by the introduction of locally interposed Ni^(+)and oxygen vacancies,resulting in a ferromagnetic ground state with the transition temperature up to 710 K.A positive magnetoresistance(7.5%)was observed in the TR-BNVO at 40 K under 7 T.These findings show that topological reduction is a powerful approach to engineer low-dimensional materials and accelerate the discovery of new quantum magnetism.
基金the National Natural Science Foun-dation of China(Grant Nos.52072244 and 12104305)the Science and Technology Commission of Shanghai Municipal-ity(Grant No.21JC1405000)the ShanghaiTech Startup Fund.This research used resources of the Advanced Photon Source,a U.S.Department of Energy(DOE)Office of Sci-ence User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No.DE-AC02-06CH11357.
文摘Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with systematically tuned atomic structures.We found that all films exhibit ferroelastic domains with four-fold symmetry and the larger domain size(higher elasticity)is always accompanied by stronger ferromagnetism.We performed synchrotron x-ray diffraction studies to investigate the backbone structure of the CoO6 octahedra,and found that both the ferromagnetism and the elasticity are simultaneously enhanced when the in-plane Co–O–Co bond angles are straightened.Therefore the study demonstrates the inextricable correlation between the ferromagnetism and ferroelasticity mediated through the octahedral backbone structure,which may open up new possibilities to develop multifunctional materials.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFB0405702)the National Natural Science Foundation of China(Grant No.51671137).
文摘Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by postgrowth thermal annealing.Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films.Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature.The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals.The results may be useful for room temperature spintronic applications based on group IV semiconductors.
基金financially supported by the National Natural Science Foundation of China (Nos. 50831002, 51271020, 51071022, and 11174031)the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT1106)+2 种基金Beijing Nova Program (No. 2011031)the Beijing Municipal Natural Science Foundation (No. 2102032)the Fundamental Research Funds for the Central Universities
文摘In this study, B-doped ZnO nanoparticles were synthesized by template-free solvothermal method. X-ray diffraction analysis reveals that B-doped ZnO nanoparti- cles have hexagonal wurtzite structure. Field emission scanning electron microscopy observations show that the nanoparticles have a diameter of 50 nm. The room tem- perature ferromagnetism increases monotonically with increasing B concentration to the ZnO nanoparticles and reaches the maximum value of saturation magnetization 0.0178 A.ma.kg-1 for 5 % B-doped ZnO nanoparticles. Moreover, photoluminescence spectra reveal that B doping causes to produce Zn vacancies （Vzn）. Magnetic moment of oxygen atoms nearest to the B-Vzn vacancy pairs can be considered as a source of ferromagnetism for B-doped ZnO nanoparticles.
基金Project supported by the Innovation Programs of the Chinese Academy of Sciences (Grant No. KJCX2-EW-W10)
文摘This study focuses on the effect of V-doping on the ferromagnetism（FM） of 6H-SiC powder.The X-ray diffraction results indicate that V is inserted into the 6H-SiC lattice.The Raman spectra reveal that with a V concentration of 25 ppm,the crystalline quality and carrier concentration of 6H-SiC are hardly varied.It is found that after the V-doping process,the saturation magnetization（Ms） and the vacancy concentration of 6H-SiC are both increased.From these results,it is deduced that the effect of V might contribute mainly to the increase of vacancy concentration,thus resulting in the increase of Ms of V-doped 6H-SiC.
基金financially supported by the National Natural Science Foundation of China(Nos.51971122,51571135 and 51701106)the National Key R&D Program of China(No.2017YFB0405703)。
文摘Two-dimensional(2 D)few-layerVSe_(2),V_(1-x)Fe_(x)Se_(2) nanosheets have been synthesized by a hightemperature organic solution-phase method. The thickness of VSe_(2) nanosheets can be tuned from 12 to 5 layers by decreasing the precursor concentrations. The few-layer VSe_(2) nanosheets show the room-temperature ferromagnetism. The coercivity and magnetization reach 0.024 T and 0.036 mA·m^(2)·g^(-1) at room temperature. The chargedensity wave behavior is also confirmed in VSe_(2) by the hysteresis loops and zero-field-cooling curve. V_(1-x)Fe_(x)Se_(2) nanosheets can be obtained by doping Fe(acac)3 in the reaction process. The room-temperature coercivity and magnetization of V_(0.8)Fe_(0.2)Se_(2) nanosheets are 5 times higher than those of the pure VSe_(2) nanosheets without destroying the structures. The enhancement of magnetization is due to the coupling interaction of 3 d orbits between V and Fe atoms. Higher Fe concentration is beneficial to improve the coercivity, which is attributed to the formation of the second phase Fe3 Se4. This simple chemical preparation method can be extended to prepare the other 2 D materials.
基金financially supported by the National Natural Science Foundation of China(No.50502005)Beijing Natural Science Foundation(No.1092014)+2 种基金Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education,Lanzhou University(LZUMMM2010002)Metallurgy Foundation of University of Science and Technology Beijingsupported by Program for New Century Excellent Talents in University(No.NCET-070065)
文摘Large-scale flower-shaped Mn doped ZnO nanostructures have been grown on silicon substrates by simple thermal evaporation at atmospheric pressure.The flower-shaped nanostructure makes up of many nanorods,which are rooted in one center.Analysis of X-ray diffraction,high-resolution transmission electron microscopy and Raman spectra results reveal that the products are of single phase with wurtzite structure.Elemental mapping results show that no impurity clusters exist in the doped materials.The photoluminescence spectra demonstrate that many oxygen vacancies exist in the doped materials,and the crystal quality is improved and the content of oxygen vacancies is decreased by annealing treatment.The flower-shaped Mn doped ZnO nanostructures exhibit ferromagnetic ordering above room temperature,and its magnetization is decreased by the annealing treatment,which indicates that the magnetic behavior of the doped materials may be related to the interaction between Mn doping and the oxygen vacancies.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61006066)the National Natural Science Foundation of China (Grant No. 11175191)
文摘Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane.By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy,Ti^3＋-V O defect complexes（or clusters） have been identified in annealed crystals at a high vacuum.We elucidate that the unpaired 3d electrons in Ti^3＋ ions provide the observed room-temperature ferromagnetism.In addition,excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.
基金Project supported by the National Natural Science Foundation of China (Grants Nos. 11004066 and 11074081)the Research Foundation for the Doctoral Program of Higher Education of China (Grant Nos. 20100142120080 and 20090142110063)
文摘We perform a first-principles study of electronic structure and magnetism of C-doped zinc-blende ZnO using the full-potential linearized augmented plane wave method. Results show that C-doped zinc-blende ZnO exhibits half-metallic ferromagnetism with a stable ferromagnetic ground state. The calculated magnetic moment of the 32-atom supercell containing one C dopant is 2.00 μ B , and the C dopant contributes most. The calculated low formation energy suggests that C-doped zinc-blende ZnO is energetically stable. The hole-mediated double exchange mechanism can be used to explain the ferromagnetism in C-doped zinc-blende ZnO.
基金Funded by the National Natural Science Foundation of China(No.61077074)
文摘The synthesis and characterization of Fe-doped CuA102 semiconductor were reported. The samples were synthesized by a simple and cost effective spin-on technique from solid state reaction of Cu20 and A1203 on sapphire （001） substrate. Appropriate ethyl-cellulose （EC） and terpineol are useful for the formation of Fe-doped CuA102 films. X-ray diffraction （XRD） revealed the growth of pure delafossite CuA102 phase ruled out elemental metallic Fe clusters in all the Fe incorporated CuA102 films. The existence of ferromagnetism at room temperature is evidenced by well-defined hysteresis loops. Specially, the saturation magnetization （Ms） values at room temperature have been monotonously enhanced with the increase of Fe composition from 1% to 5%.
基金financially supported by the Anhui Provincial Natural Science Foundation (No. 1508085SME219)
文摘Gear-shape CeO2 microstructures have been synthesized via a facile hydrothermal method with Ce（NO3）3-6H20 as the cerium source, NHaHCO3 as both the precipitator and the carbon source, and cetyltrimethyl ammonium bromide （CTAB） as the surfactant. X-ray diffraction （XRD） inferred that the synthesized CeO2 microstructures exhibited a fluorite structure. The band gap （Eg） of CeO2 samples is larger than that of bulk. X-ray photoelectron spectroscopy （XPS） showed that there are plenty or Ce3＋ ions and oxygen vacancies at the surface of CeO2 samples. All the synthesized CeO2 samples exhibited the room temperature ferromagnetism, and the saturation magnetization increases with the increases of lattice parameter and Eg. The room temperature ferromagnetism mechanism of gear-shape CeO2 is mainly attributed to the influence Ce3＋ ions.
文摘Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the most promising candidates for next-generation low-cost, high-performance and nano-scale spintronic applications such as spin field-effect transistors and quantum computation/communication. However, as one of the 125 important scientific issues raised by Science journal in 2005 that "is it possible to create magnetic semiconductors that work at room temperature?", how to achieve a feasible ferromagnetic semiconductor with high Curie temperature is still a long-standing challenge despite of tremendous efforts have been devoted in this field since 1960s. The recent discovery of 2D ferromagnetic semiconductors Cr2Ge2Te6 and CrI3 has evoked new research interests in 2D intrinsic ferromagnetic semiconductors. But the low Curie temperature (<45 K) of these materials is still badly hindering their industrial applications.
基金Project supported by the Special Fund for Major State Basic Research Project (G2000068305), the Hi-Tech Research Project (2004AA31G050), and the National Natural Science Foundation of China (60390072)
文摘The magnetic and structural properties of 2% Ni-doped ZnO powers prepared by sol-gel method were studied. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) of the sample do not show existence of any signal of second phase. The X-photoelectron spectroscopy (XPS) of the sample shows the chemical valence of Ni is +2 and the real Ni concentration is 2.19% determined by X-ray fluorescence spectra (XRFS). The magnetic property performed with superconducting quantum interference device (SQUID) shows that the sample exhibits ferromagnetism above room temperature and the Curie temperature (TC) is about 600 K.
基金supported by National Natural Science Foundation of China(Nos.21271082 and 21371068).
文摘In this paper,a hydrothermal approach is utilized for the first time in integrating graphene oxide(GO),acetic acid(HAc)and nickel foam to prepare hydrogenated graphene(HG).There are two primary aims of this study:one is to ascertain the structure of the as-prepared HG,and the other one is to investigate the ferromagnetism of the HG.Under hydrothermal conditions,GO was reduced and hydrogenated by HAc,while the nickel foam served as a catalyst.This work provides a novel and facile route for the synthesis of hydrogenated graphene,which may lead to the application of hydrogenated graphene in spin electronic devices.
基金Funded by the National Natural Science Foundation of China(No.61077074)
文摘One-dimensional, diluted magnetic semiconductor nanofibers have attracted increasing attention for their unique magnetic properties, large specific surface area, and high porosity. These qualities lead to excellent performance in magneto-optical devices, magnetic resonance imaging, ferrofluids and magnetic separation. The purpose of this study is to fabricate P-type one dimensional CuAlO2-based diluted magnetic semiconductor nanofibers. First, we fabricated CuAl0.95Co0.05O2 nanofibers with an average diameter of 1 μm with the electrospinning method. The annealed nanofibers were thermally treated at a temperature of 1 100℃ and then shrunk to a diameter of about 650 nm. We used X-ray diffraction measurements and Raman spectra to confirm that the CUAl0.95CO0.05O2 nanofihers had a single impurity free delafossite phase. The X-ray photoelectron spectroscopy analysis indicates that Co was present in the ＋2 oxidation state, resulting in an room temperature ferromagnetism in the CHAl0.95Co0.05O2 fiber. This contrststs with nonmagnetism in pristine CuAlO2 fiber. The coercivity （Hc） value of 65.26 Oe and approximate saturation magnetization （Ms） of 0.012 emu/g demonstrate good evidence of ferromagnetism at room temperature for CuAl0.95Co0.05O2 nanofibers.
文摘Nanopowders of Znl_x_y_zMnxNiyLizO [（x = 0.04, y = 0, z = 0）, （x = 0.04, y = 0.03, z = 0） and （x = 0.04, y = 0.03, z = 0.03）] have been synthesized by sol-gel precursor route using ethylene diamine tetraacetic acid （EDTA） as a metal chelating agent. X-ray diffraction analysis confirms the formation of wurtzite hexagonal structure for all the three compositions. Mn2＋ doped ZnO exhibits room temperature ferromagnetism （RTFM）, and it is found that further Ni2＋ doping has decreased Ms because of limit of solid solubility of transition metal in ZnO. But codoping of monovalent Li1＋, further increases the ferromagnetism （FM） value, due to introduction of free carriers compared to the dual doped samples. Photoluminescence （PL） spectra of the system, exhibit near band edge （NBE） emission peak at --464 nm due to the electron transition from interstitials to the valence band. Recombination of conduction electron with hole trapped at oxygen vacancy, leads to prominent defect emission peaks at --482 nm and 532 nm. The evidence of the formation of metaI-EDTA complexes are found from the Fourier transform infrared spectra at 2800-3800 cm-1 with shifting, splitting of the peak and also drastic variations in the intensity.
基金the National Natural Science Foundation of China (No. 20373073)the National Basic Research Program of China (No. 2004CB720605)the Fund of Fujian Key Laboratory of Nanomaterials (No. 2006L2005)
文摘We present a first principle study of Cr-doped In2O3 system using density functional theory. The obtained results show that the Cr ion prefers the cation site of the center of trigonally distorted octahedron and converges to high spin-polarized configuration in the ground state. The hybridization between d-states and the donor states is strong, and the spin-split donor impurity-band model is found to be the most favorable mechanism for the ferromagnetism in this system. The good ferromagnetic property of high Curie temperature is discussed in view of the electronic structure analyses.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61274128)the Natural Science Foundation of Chongqing City, China (Grant Nos. 2011BA4031 and 2013jjB0023)+1 种基金the Education Commission of Chongqing City, China (Grant No. KJ120608)the Chongqing Normal University,China (Grant No. 09XLS04)
文摘First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the total magnetic mo- ment mainly originates from the p--d hybridization of Cu-N and Cu-O as well as p--p coupling interaction between N and O at the Fermi level. The Zn34Cu2035N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the （Cu, N）-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.
