Ga^＋ ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance （MR） are investigated. The results show tha...Ga^＋ ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance （MR） are investigated. The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose. The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10^13 ions/cm^2 and the step disappears afterwards. Two oeaks in the R-H curve are found to be asymmetric.展开更多
The eigenspectrum and eigenvectors of the ^(2)F_(7/2) ground multiplets of two structural isomer coordination complexes,Yb(trenovan)(H_(3)trenovan=tris(((3-methoxysalicylidene)amino)ethyl)amine)and Yb(trenpvan)(H_(3)t...The eigenspectrum and eigenvectors of the ^(2)F_(7/2) ground multiplets of two structural isomer coordination complexes,Yb(trenovan)(H_(3)trenovan=tris(((3-methoxysalicylidene)amino)ethyl)amine)and Yb(trenpvan)(H_(3)trenpvan=tris(((5-methoxysalicylidene)amino)ethyl)amine),were determined by use of magnetometry,electron paramagnetic resonance and luminescence spectroscopies.The two 4f complexes crystallise in the trigonal P3space group,have identical chemical formulas and differ only in the placement of the methoxy group on the aromatic ring of salicylaldehyde,with it being either ortho,Yb(trenovan),or para,Yb(trenpvan),to the phenoxo group.This structural isomerism is found to have a profound influence on the solid state static and dynamic magnetic properties of the complexes.In the bulk,both isomers display a combination of direct and Raman magnetisation relaxation proccesses,however,at vastly different rates.Magnetic dilution in an isostructural diamagnetic host supresses the occurrence of the direct process suggesting that the direct process observed in the bulk originates from Yb_((III))centres coupled by magnetic dipole interactions.The eigenspectrum,eigenvectors and spin lattice relaxation of Yb(trenpvan)are found to be closer to the ones found in Yb(trensal)(H_(3)trensal=tris(((salicylidene)amino)ethyl)amine)where the methoxy group is substituted by an H atom,than to those of Yb(trenovan)where the methoxy group is in the ortho position.Thus,the position of chemical modifications has a tremendous influence on the static and dynamic solid state magnetic properties of 4f coordination complexes.Our detailed study on single crystals,demonstrates that the rarely studied effect of modifications of the position of second coordination sphere chemical groups on the dynamic magnetic properties can in fact be used to chemically tune the magnetisation dynamics of 4f spin systems.展开更多
We report the luminescence and magnetic properties of the mononuclear Dy(Ⅲ)complex[DyTp_(2)Acac](Tp=tris-pyrazolylborohydride and Acac=2,4-pentanedionate).This complex displays peculiar slow magnetisation dynamics at...We report the luminescence and magnetic properties of the mononuclear Dy(Ⅲ)complex[DyTp_(2)Acac](Tp=tris-pyrazolylborohydride and Acac=2,4-pentanedionate).This complex displays peculiar slow magnetisation dynamics at low temperature in the absence of a static field,which we managed to interpret using its resolved luminescence spectrum and ab initio calculations.展开更多
To improve the overall magnetic properties of Sm(CoFeCuZr)_(z)sintered magnets,a dual-alloy sintering process that involves mixing high-iron,low-copper powders with low-iron,high-copper powders was systematically inve...To improve the overall magnetic properties of Sm(CoFeCuZr)_(z)sintered magnets,a dual-alloy sintering process that involves mixing high-iron,low-copper powders with low-iron,high-copper powders was systematically investigated.The results demonstrate that this method significantly improves the Cu-lean phenomenon at the grain boundaries,achieves multiscale uniform microstructures,greatly enhances the pinning field strength,and ultimately produces a high-performance dual-alloy magnet with a maximum energy product((BH)_(max))exceeding 240 kJ/m^(3)and an intrinsic coercivity(H_(cj))exceeding 2400 kA/m.In particular,when 35 wt.%of low-iron,high-copper alloy powder is incorporated,the dual-alloy magnet achieves a remanence of 1.13 T,H_(cj)of 2691.2 kA/m and(BH)_(max)of 248 kJ/m^(3).To evaluate the overall magnetic performance,the sum of H_(cj)(in kA/m)and(BH)_(max)(in kJ/m^(3))is used as a combined parameter,yielding a value of 2939.2.Compared with single-alloy magnets of the same composition,the dual-alloy sintering process yields magnets with a more uniform elemental distribution and superior magnetic properties.展开更多
Nanocrystalline Fe 25 Ni 75 powders were prepared by the mechanical alloying process . They were investigated by X ray diffraction and magnetic measurements .The ball milling time dependence of grain size, i...Nanocrystalline Fe 25 Ni 75 powders were prepared by the mechanical alloying process . They were investigated by X ray diffraction and magnetic measurements .The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe 25 Ni 75 alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10-20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10-20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.展开更多
Based on the scales transformation of electromagnetic theory, the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic p...Based on the scales transformation of electromagnetic theory, the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter. The obtained results are in good agreement with that in the literature. The angle between the direction of inside field and that of outside field is derived. In S wave band, calculations for the effects induced by parameters of the inner field are established. Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably. The inner field will increase as the electron density increases. The inner field varies with frequency nonlinearly. There is an angle between the inner field and the incident field, it changes nonlinearly with the frequency.展开更多
A weakly magnetized sheath for a collisionless, electronegative plasma comprising positive ions,electrons, and negative ions is investigated numerically using the fluid approach. The electrons are considered to be non...A weakly magnetized sheath for a collisionless, electronegative plasma comprising positive ions,electrons, and negative ions is investigated numerically using the fluid approach. The electrons are considered to be non-Maxwellian in nature and are described by Tsalli's distribution. Such electrons have a substantial effect on the sheath properties. The study also reveals that non-Maxwellian distribution is the most realistic description for negative ions in the presence of an oblique magnetic field. In addition to the negative ion temperature, the sheath potential is also affected by the nonextensive parameters. The present research finds application in the plasma processing and semiconductor industry as well as in space plasmas.展开更多
We report the synthesis,spectroscopic and magnetic characterisation and ab initio investigation of a new mononuclear ytterbium based complex,[YbTp_(2)NO_(3)],and discuss the physical mechanisms underlying the slow rel...We report the synthesis,spectroscopic and magnetic characterisation and ab initio investigation of a new mononuclear ytterbium based complex,[YbTp_(2)NO_(3)],and discuss the physical mechanisms underlying the slow relaxation of its magnetisation in a moderate static field and at low temperature.展开更多
Accommodating disparate spin centres within a single ensemble is a valuable synthetic strategy to obtaininteresting molecular magnetic materials.3d–4f heterometallic complexes are one such subclass that hasbeen exten...Accommodating disparate spin centres within a single ensemble is a valuable synthetic strategy to obtaininteresting molecular magnetic materials.3d–4f heterometallic complexes are one such subclass that hasbeen extensively explored for the last three decades owing to their interesting magnetic properties.Theprimary reason is that the bridging ligand mediates magnetic super-exchange between 3d and 4f ions toconsiderably reduce the prevalent quantum tunnelling of magnetisation(QTM)in such complexes.Among the 3d–4f family,Cr^(Ⅲ)–Ln^(Ⅲ) assemblies nicely demonstrate the pivotal role played by strongexchange interactions between these two individual spin carriers to engender interesting single-moleculemagnet(SMM)properties.In fact,this part of heterometallic chemistry has flourished greatly in the lastdecade despite its late development.In this review we provide an extensive synthetic,structural,magnetic,and magnetocaloric description of various Cr^(Ⅲ)–Ln^(Ⅲ) complexes along with their fundamental mecha-nisms of exchange interaction.Finally,we provide some possible solutions to improve the SMM propertiesof the Cr^(Ⅲ)–Ln^(Ⅲ) and other heterometallic complexes.展开更多
We present a general relationship between the magnetisation blocking temperature(T_(B))measured using the zero-field cooling/field cooling technique(ZFC/FC)and the temperature-dependent spin relaxation time obtained f...We present a general relationship between the magnetisation blocking temperature(T_(B))measured using the zero-field cooling/field cooling technique(ZFC/FC)and the temperature-dependent spin relaxation time obtained from AC susceptibility and magnetisation decay measurements.The presented mathematical approach supplies ZFC/FC blocking temperatures at any heating rate(R_(H)),providing comparable values to those obtained experimentally,as demonstrated by testing 107 examples for reported singlemolecule magnets(SMMs)where the ZFC/FC curve has been measured.This procedure is examined in further detail for a new single-molecule magnet,[Dy(OPAd_(2)Bz)_(2)(H_(2)O)4Br]Br_(2)·4THF(1)(OPAd_(2)Bz:di(1-adamantyl)benzylphosphine oxide).For this compound,ZFC/FC measurements were made over a broad range of heating rates(0.01-5 K min^(−1)),which agreed with the general behaviour predicted from AC susceptibility data.We discuss how the demagnetisation mechanism determines the sensitivity of T_(B)with respect to the heating rate:T_(B)is mostly insensitive to R_(H)for Orbach relaxation,while there is a larger sensitivity for Raman-limited systems.Our conclusions provide a clear physical interpretation of ZFC/FC blocking temperatures,aiding in the proper contextualization of this figure of merit.展开更多
Magnetic nanowires(NWs)are ideal materials for the fabrication of various multifunctional nanostructures which can be manipulated by an external magnetic fi eld.Highly crystalline and textured nanowires of nickel(Ni N...Magnetic nanowires(NWs)are ideal materials for the fabrication of various multifunctional nanostructures which can be manipulated by an external magnetic fi eld.Highly crystalline and textured nanowires of nickel(Ni NWs)and cobalt(Co NWs)with high aspect ratio(~330)and high coercivity have been synthesized by electrodeposition using nickel sulphate hexahydrate(NiSO_(4)·6H_(2)O)and cobalt sulphate heptahydrate(CoSO_(4)·7H_(2)O)respectively on nanoporous alumina membranes.They exhibit a preferential growth along〈110〉.A general mobility assisted growth mechanism for the formation of Ni and Co NWs is proposed.The role of the hydration layer on the resulting one-dimensional geometry in the case of potentiostatic electrodeposition is verified.A very high interwire interaction resulting from magnetostatic dipolar interactions between the nanowires is observed.An unusual low-temperature magnetisation switching for fi eld parallel to the wire axis is evident from the peculiar high fi eld M(T)curve.展开更多
Advanced Monte Carlo simulations of magnetisation and susceptibility in 3D XY model are performed at two different coupling constantsβ=0.55 andβ=0.5,completing our previous simulation results with additional data po...Advanced Monte Carlo simulations of magnetisation and susceptibility in 3D XY model are performed at two different coupling constantsβ=0.55 andβ=0.5,completing our previous simulation results with additional data points and extending the range of the external field to twice as small values as previously reported(h≥0.00015625).The simulated maximal lattices sizes are also increased from L=384 to L=512.Our aim is an improved estimation of the exponentρ,describing the Goldstone mode singularity M(h)=M(+0)+chρat h→0,where M is the magnetisation.The data reveal some unexpected small oscillations.It makes the estimation by manyparameter fits of the magnetisation data unstable,and we are looking for an alternative method.Our best estimateρ=0.555(17)is extracted from the analysis of effective exponents determined from local fits of the susceptibility data.This method gives stable and consistent results for both values ofβ,taking into account the leading as well as the subleading correction to scaling.We report also the values of spontaneous magnetisation.展开更多
REBCO tapes carry DC current under AC magnetic fields in proposed HTS fusion applications. AC loss will be generated in the process and it is important to understand the AC loss behaviour for safe operation of the fus...REBCO tapes carry DC current under AC magnetic fields in proposed HTS fusion applications. AC loss will be generated in the process and it is important to understand the AC loss behaviour for safe operation of the fusion magnets. In this work, magnetisation loss (Qm), dynamic resistance (Rdyn), and total loss (Qtotal) in four different REBCO tapes are numerically studied, using the measured and , for the magnetic field amplitude applied perpendicularly up to 8 T at 20 K and 50 K, where represents the magnetic field and field angle () dependent critical current density. The peak of Theva data is different from that of other tapes. We artificially shifted the ab-plane peak of Theva to the left by 25° to match the peak value. The newly shifted data is named as Theva-shift, which was also investigated to study the influence of the Theva peak shift on AC loss. The normalised DC transport current level (i = It/Ic0) ranges from 0.05 to 0.9, where the DC current amplitude and the self-critical current of the tape are represented by It and Ic0, respectively. The simulation results show that the AC losses deviate significantly from the Brandt-Indenbom (BI) equation at high magnetic fields. Jc and instantaneous loss curves for different tapes show correlation at high magnetic fields. The simulation results also show how different characteristics for different tapes influence AC losses. When AC loss values are scaled by the self-field critical current, Qm without current and Qtotal with current in the different tapes show a good agreement. It implies that the temperature dependence of the two types of loss can be calculated from a known loss at one temperature and the self-field critical current.展开更多
1.Introduction It is now generally recognized that measurements of the directions of magnetisation of samples from a magnetically stable rock formation allow the direction of the Earth’s magnetic field at the time wh...1.Introduction It is now generally recognized that measurements of the directions of magnetisation of samples from a magnetically stable rock formation allow the direction of the Earth’s magnetic field at the time when the rock was formed to be determined.The direction of the Earth’s magnetic field has been recorded at observatories in many places over the past few hundred years,and from an analysis of these records it is possible to recognise two components in the geomagnetic field:the first being approximately that of a dipole at the centre of the Earth with its axis along the axis of rotation,and the second a much smaller non-dipole component which undergoes variations with periods of the order of hundreds of years.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 50671048)
文摘Ga^＋ ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance （MR） are investigated. The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose. The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10^13 ions/cm^2 and the step disappears afterwards. Two oeaks in the R-H curve are found to be asymmetric.
基金Novo Nordisk Foundation for research grant NNF20OC0065610 under the Natural and Technical Sciences programme.
文摘The eigenspectrum and eigenvectors of the ^(2)F_(7/2) ground multiplets of two structural isomer coordination complexes,Yb(trenovan)(H_(3)trenovan=tris(((3-methoxysalicylidene)amino)ethyl)amine)and Yb(trenpvan)(H_(3)trenpvan=tris(((5-methoxysalicylidene)amino)ethyl)amine),were determined by use of magnetometry,electron paramagnetic resonance and luminescence spectroscopies.The two 4f complexes crystallise in the trigonal P3space group,have identical chemical formulas and differ only in the placement of the methoxy group on the aromatic ring of salicylaldehyde,with it being either ortho,Yb(trenovan),or para,Yb(trenpvan),to the phenoxo group.This structural isomerism is found to have a profound influence on the solid state static and dynamic magnetic properties of the complexes.In the bulk,both isomers display a combination of direct and Raman magnetisation relaxation proccesses,however,at vastly different rates.Magnetic dilution in an isostructural diamagnetic host supresses the occurrence of the direct process suggesting that the direct process observed in the bulk originates from Yb_((III))centres coupled by magnetic dipole interactions.The eigenspectrum,eigenvectors and spin lattice relaxation of Yb(trenpvan)are found to be closer to the ones found in Yb(trensal)(H_(3)trensal=tris(((salicylidene)amino)ethyl)amine)where the methoxy group is substituted by an H atom,than to those of Yb(trenovan)where the methoxy group is in the ortho position.Thus,the position of chemical modifications has a tremendous influence on the static and dynamic solid state magnetic properties of 4f coordination complexes.Our detailed study on single crystals,demonstrates that the rarely studied effect of modifications of the position of second coordination sphere chemical groups on the dynamic magnetic properties can in fact be used to chemically tune the magnetisation dynamics of 4f spin systems.
基金ANR(REDIVALAN ANR-15-CE29-0019-02 and SCOSIMLIGHT ANR-13-BS07-0022-01).
文摘We report the luminescence and magnetic properties of the mononuclear Dy(Ⅲ)complex[DyTp_(2)Acac](Tp=tris-pyrazolylborohydride and Acac=2,4-pentanedionate).This complex displays peculiar slow magnetisation dynamics at low temperature in the absence of a static field,which we managed to interpret using its resolved luminescence spectrum and ab initio calculations.
基金supported by the National Key Research and Development Program for Young Scientists,China(No.2023YFB3508400)the National Natural Science Foundation of China(Nos.51871005,51931007)+1 种基金the Key Program of Science and Technology Development Project of Beijing Municipal Education Commission of China(No.KZ202010005009)the Program of Top Disciplines Construction in Beijing,China(No.PXM2019_014204_500031)。
文摘To improve the overall magnetic properties of Sm(CoFeCuZr)_(z)sintered magnets,a dual-alloy sintering process that involves mixing high-iron,low-copper powders with low-iron,high-copper powders was systematically investigated.The results demonstrate that this method significantly improves the Cu-lean phenomenon at the grain boundaries,achieves multiscale uniform microstructures,greatly enhances the pinning field strength,and ultimately produces a high-performance dual-alloy magnet with a maximum energy product((BH)_(max))exceeding 240 kJ/m^(3)and an intrinsic coercivity(H_(cj))exceeding 2400 kA/m.In particular,when 35 wt.%of low-iron,high-copper alloy powder is incorporated,the dual-alloy magnet achieves a remanence of 1.13 T,H_(cj)of 2691.2 kA/m and(BH)_(max)of 248 kJ/m^(3).To evaluate the overall magnetic performance,the sum of H_(cj)(in kA/m)and(BH)_(max)(in kJ/m^(3))is used as a combined parameter,yielding a value of 2939.2.Compared with single-alloy magnets of the same composition,the dual-alloy sintering process yields magnets with a more uniform elemental distribution and superior magnetic properties.
文摘Nanocrystalline Fe 25 Ni 75 powders were prepared by the mechanical alloying process . They were investigated by X ray diffraction and magnetic measurements .The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe 25 Ni 75 alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10-20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10-20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60971079)the Natural Science Foundation of Shaanxi Province of China (Grant No. 2009JM8020)the Natural Science Foundation of Shaanxi Educational Office of China (Grant No. 09JK800)
文摘Based on the scales transformation of electromagnetic theory, the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter. The obtained results are in good agreement with that in the literature. The angle between the direction of inside field and that of outside field is derived. In S wave band, calculations for the effects induced by parameters of the inner field are established. Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably. The inner field will increase as the electron density increases. The inner field varies with frequency nonlinearly. There is an angle between the inner field and the incident field, it changes nonlinearly with the frequency.
文摘A weakly magnetized sheath for a collisionless, electronegative plasma comprising positive ions,electrons, and negative ions is investigated numerically using the fluid approach. The electrons are considered to be non-Maxwellian in nature and are described by Tsalli's distribution. Such electrons have a substantial effect on the sheath properties. The study also reveals that non-Maxwellian distribution is the most realistic description for negative ions in the presence of an oblique magnetic field. In addition to the negative ion temperature, the sheath potential is also affected by the nonextensive parameters. The present research finds application in the plasma processing and semiconductor industry as well as in space plasmas.
基金ANR(REDIVALAN ANR-15-CE29-0019-02 and SCOSIMLIGHT ANR-13-BS07-0022-01)for financial support.
文摘We report the synthesis,spectroscopic and magnetic characterisation and ab initio investigation of a new mononuclear ytterbium based complex,[YbTp_(2)NO_(3)],and discuss the physical mechanisms underlying the slow relaxation of its magnetisation in a moderate static field and at low temperature.
基金support from the SERB-DST Early Career Research Award(ECR)with Project Number ECR/2016/001746.
文摘Accommodating disparate spin centres within a single ensemble is a valuable synthetic strategy to obtaininteresting molecular magnetic materials.3d–4f heterometallic complexes are one such subclass that hasbeen extensively explored for the last three decades owing to their interesting magnetic properties.Theprimary reason is that the bridging ligand mediates magnetic super-exchange between 3d and 4f ions toconsiderably reduce the prevalent quantum tunnelling of magnetisation(QTM)in such complexes.Among the 3d–4f family,Cr^(Ⅲ)–Ln^(Ⅲ) assemblies nicely demonstrate the pivotal role played by strongexchange interactions between these two individual spin carriers to engender interesting single-moleculemagnet(SMM)properties.In fact,this part of heterometallic chemistry has flourished greatly in the lastdecade despite its late development.In this review we provide an extensive synthetic,structural,magnetic,and magnetocaloric description of various Cr^(Ⅲ)–Ln^(Ⅲ) complexes along with their fundamental mecha-nisms of exchange interaction.Finally,we provide some possible solutions to improve the SMM propertiesof the Cr^(Ⅲ)–Ln^(Ⅲ) and other heterometallic complexes.
基金FONDECYT Regular 1210325 for financial support.Powered@NLHPC:this research was partially supported by the supercomputing infrastructure of the NLHPC(ECM-02)Financial support from the Ministerio de Ciencia e Innovación(projects PID2022-138090NB-C21,PID2021-122464NB-I00,TED2021-129593B-I00,CNS2023-144561 and Maria de Maeztu CEX2021-001202-M)+5 种基金the Junta de Andalucía(FQM-195 and FQM-337)FEDER/Junta de Andalucía(projects I+D+i P20_00692,C-EXP-140-UGR23 and M.1.B.B TA_000722,Programas Operativos FEDER 2014-2020 y 2021-2027,Consejería de Economía,Conocimiento,Empresas y Universidad)the University of Granada(project I+D+i PPJIA2020.10)is greatly appreciatedthe Centro de Servicios de Informática y Redes de Comunicaciones(CSIRC)for computational time and facilitiesthe Ministerio de Ciencia e Innovación for a Ramón y Cajal contract(the publication is part of the project PID2022-138090NB-C21 and grant RYC2021-034288-I funded by MCIN/AEI/10.13039/501100011033 and by the European Union“NextGenerationEU”/PRTR”)the Generalitat de Catalunya for ICREA Academia and 2021-SGR-00286 grants,and for computational resources at CSUC.
文摘We present a general relationship between the magnetisation blocking temperature(T_(B))measured using the zero-field cooling/field cooling technique(ZFC/FC)and the temperature-dependent spin relaxation time obtained from AC susceptibility and magnetisation decay measurements.The presented mathematical approach supplies ZFC/FC blocking temperatures at any heating rate(R_(H)),providing comparable values to those obtained experimentally,as demonstrated by testing 107 examples for reported singlemolecule magnets(SMMs)where the ZFC/FC curve has been measured.This procedure is examined in further detail for a new single-molecule magnet,[Dy(OPAd_(2)Bz)_(2)(H_(2)O)4Br]Br_(2)·4THF(1)(OPAd_(2)Bz:di(1-adamantyl)benzylphosphine oxide).For this compound,ZFC/FC measurements were made over a broad range of heating rates(0.01-5 K min^(−1)),which agreed with the general behaviour predicted from AC susceptibility data.We discuss how the demagnetisation mechanism determines the sensitivity of T_(B)with respect to the heating rate:T_(B)is mostly insensitive to R_(H)for Orbach relaxation,while there is a larger sensitivity for Raman-limited systems.Our conclusions provide a clear physical interpretation of ZFC/FC blocking temperatures,aiding in the proper contextualization of this figure of merit.
文摘Magnetic nanowires(NWs)are ideal materials for the fabrication of various multifunctional nanostructures which can be manipulated by an external magnetic fi eld.Highly crystalline and textured nanowires of nickel(Ni NWs)and cobalt(Co NWs)with high aspect ratio(~330)and high coercivity have been synthesized by electrodeposition using nickel sulphate hexahydrate(NiSO_(4)·6H_(2)O)and cobalt sulphate heptahydrate(CoSO_(4)·7H_(2)O)respectively on nanoporous alumina membranes.They exhibit a preferential growth along〈110〉.A general mobility assisted growth mechanism for the formation of Ni and Co NWs is proposed.The role of the hydration layer on the resulting one-dimensional geometry in the case of potentiostatic electrodeposition is verified.A very high interwire interaction resulting from magnetostatic dipolar interactions between the nanowires is observed.An unusual low-temperature magnetisation switching for fi eld parallel to the wire axis is evident from the peculiar high fi eld M(T)curve.
文摘Advanced Monte Carlo simulations of magnetisation and susceptibility in 3D XY model are performed at two different coupling constantsβ=0.55 andβ=0.5,completing our previous simulation results with additional data points and extending the range of the external field to twice as small values as previously reported(h≥0.00015625).The simulated maximal lattices sizes are also increased from L=384 to L=512.Our aim is an improved estimation of the exponentρ,describing the Goldstone mode singularity M(h)=M(+0)+chρat h→0,where M is the magnetisation.The data reveal some unexpected small oscillations.It makes the estimation by manyparameter fits of the magnetisation data unstable,and we are looking for an alternative method.Our best estimateρ=0.555(17)is extracted from the analysis of effective exponents determined from local fits of the susceptibility data.This method gives stable and consistent results for both values ofβ,taking into account the leading as well as the subleading correction to scaling.We report also the values of spontaneous magnetisation.
基金NZ Royal Society Marsden under Grant MFP-VUW2205New Zealand Ministry of Business,Innovation and Employment under the Advanced Energy Technology Platform program“High power electric motors for large scale transport”under Grant RTVU2004.
文摘REBCO tapes carry DC current under AC magnetic fields in proposed HTS fusion applications. AC loss will be generated in the process and it is important to understand the AC loss behaviour for safe operation of the fusion magnets. In this work, magnetisation loss (Qm), dynamic resistance (Rdyn), and total loss (Qtotal) in four different REBCO tapes are numerically studied, using the measured and , for the magnetic field amplitude applied perpendicularly up to 8 T at 20 K and 50 K, where represents the magnetic field and field angle () dependent critical current density. The peak of Theva data is different from that of other tapes. We artificially shifted the ab-plane peak of Theva to the left by 25° to match the peak value. The newly shifted data is named as Theva-shift, which was also investigated to study the influence of the Theva peak shift on AC loss. The normalised DC transport current level (i = It/Ic0) ranges from 0.05 to 0.9, where the DC current amplitude and the self-critical current of the tape are represented by It and Ic0, respectively. The simulation results show that the AC losses deviate significantly from the Brandt-Indenbom (BI) equation at high magnetic fields. Jc and instantaneous loss curves for different tapes show correlation at high magnetic fields. The simulation results also show how different characteristics for different tapes influence AC losses. When AC loss values are scaled by the self-field critical current, Qm without current and Qtotal with current in the different tapes show a good agreement. It implies that the temperature dependence of the two types of loss can be calculated from a known loss at one temperature and the self-field critical current.
文摘1.Introduction It is now generally recognized that measurements of the directions of magnetisation of samples from a magnetically stable rock formation allow the direction of the Earth’s magnetic field at the time when the rock was formed to be determined.The direction of the Earth’s magnetic field has been recorded at observatories in many places over the past few hundred years,and from an analysis of these records it is possible to recognise two components in the geomagnetic field:the first being approximately that of a dipole at the centre of the Earth with its axis along the axis of rotation,and the second a much smaller non-dipole component which undergoes variations with periods of the order of hundreds of years.
