Our recent progress on magnetic entropy change(S) involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and au...Our recent progress on magnetic entropy change(S) involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and austenite exhibit ferromagnetic(FM) behavior but show different magnetic anisotropies,a positive S as large as 4.1 J·kg^-1·K^-1 under a field change of 0-0.9 T was first observed at martensitic transition temperature T M~197 K.Through adjusting the Ni:Mn:Ga ratio to affect valence electron concentration e/a,T M was successfully tuned to room temperature,and a large negative S was observed in a single crystal.The △S attained 18.0 J·kg^-1·K^-1 under a field change of 0-5 T.We also focused on the metamagnetic alloys that show mechanisms different from the conventional ones.It was found that post-annealing in suitable conditions or introducing interstitial H atoms can shift the T M across a wide temperature range while retaining the strong metamagnetic behavior,and hence,retaining large magnetocaloric effect(MCE) and magnetoresistance(MR).The melt-spun technique can disorder atoms and make the ribbons display a B2 structure,but the metamagnetic behavior,as well as the MCE,becomes weak due to the enhanced saturated magnetization of martensites.We also studied the effect of Fe/Co co-doping in Ni 45(Co1-xFex)5 Mn36.6In13.4 metamagnetic alloys.Introduction of Fe atoms can assist the conversion of the Mn-Mn coupling from antiferromagnetic to ferromagnetic,thus maintaining the strong metamagnetic behavior and large MCE and MR.Furthermore,a small thermal hysteresis but significant magnetic hysteresis was observed around TM in Ni51Mn49-xInx metamagnetic systems,which must be related to different nucleation mechanisms of structural transition under different external perturbations.展开更多
This paper presents a study of the inverse magnetocaloric effect (MCE) corresponding to martensitic transition using various experimental approaches for Ni46Cu4Mn38Sn12 and NisoCoMn34In]5 Heusler alloy. Through heat...This paper presents a study of the inverse magnetocaloric effect (MCE) corresponding to martensitic transition using various experimental approaches for Ni46Cu4Mn38Sn12 and NisoCoMn34In]5 Heusler alloy. Through heat capacity measurements, it is found that the "giant inverse MCE" upon martensitic transition evaluated by the Maxwell relation in these alloys are unphysical results. This is due to the coexistence of both martensitic and austenitic phases, as well as thermal hysteresis during martensitic transition. However, careful study indicates that the spurious results during martensitic transition can be removed using a Clausius Clapeyron equation based on magnetization measurements.展开更多
The total energy, electronic structures, and magnetisms of the Al Cu2Mn-type Co2TiSb1-xSnx(x = 0, 0.25, 0.5) with the different lattice parameter ratios of c/a are studied by using the first-principles calculations....The total energy, electronic structures, and magnetisms of the Al Cu2Mn-type Co2TiSb1-xSnx(x = 0, 0.25, 0.5) with the different lattice parameter ratios of c/a are studied by using the first-principles calculations. It is found that the phase transformation from the cubic to the tetragonal structure lowers the total energy, indicating that the martensitic phase is more stable and that a phase transition from austenite to martensite may happen at a lower temperature. Thus, a ferromagnetic shape memory effect can be expected to occur in these alloys. The Al Cu2Mn-type Co2TiSb1-xSnx(x = 0, 0.25, 0.5) alloys are weak ferrimagnets in the austenitic phase and martensitic phase.展开更多
Nowadays,searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields,such as solid-state refrigeration,magnetic actuators,magnetic sensors and inte...Nowadays,searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields,such as solid-state refrigeration,magnetic actuators,magnetic sensors and intelligent/smart devices.In this work,the magnetic-field-induced metamagnetic reverse martensitic transformation(MFIRMT)from paramagnetic martensite to ferromagnetic austenite with multiple magneto-responsive effects is realized in Fe-doped Co-V-Ga Heusler alloys by manipulating the magnetic ordering.The martensitic transformation temperature Tmreduces quasi-linearly with increasing Fe-content.In strikingly contrast with the Fe-free alloys,the magnetization difference(M')across martensitic transformation increases by three orders of magnitude for Fe-doped alloys.The increased M'should be ascribed to the reduction of Tm,almost unchanged Curie temperature of austenite and the increased magnetic moment in the samples with higher Fe-content.The large M'provides strong driving force to realize the MFIRMT and accordingly multiple magneto-responsive effects,such as magnetocaloric,magnetoresistance and magnetostriction effects.Meanwhile,giant Vickers hardness of 518 HV and compressive strength of 1423 MPa are achieved.Multiple magneto-responsive effects with exceptional mechanical properties make these alloys great potential candidates for applications in many fields.展开更多
The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125...The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125,0.25,0.375,y=0.625)]alloys were systematically studied by the first-principles calculations.For the formation energy,the martensite is smaller than the austenite,the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation.The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) (y<0.625) alloys.When y=0.625 in the Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) series,the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state.Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy.Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance,but reduce the toughness in the Ni–Mn–Cu–Ti alloy.And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys.The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.展开更多
There are various new structures with superior performance for Heusler alloy materials that are widely used in spintronic materials,thermoelectric materials,and other fields.In this study,three new Ag-based full-Heusl...There are various new structures with superior performance for Heusler alloy materials that are widely used in spintronic materials,thermoelectric materials,and other fields.In this study,three new Ag-based full-Heusler alloys(Ag 2 TiGa,Ag 2 VGa,and Ag 2 TiTl)are proposed.The stability,mechanical properties,and electronic proper-ties of these three new Ag-based Heusler alloys were studied using first-principles calculations.The results showed that the compression resistance,shear resistance,stiffness,and elastic anisotropy of Ag 2 VGa were greater than those of Ag 2 TiGa and Ag 2 TiTl,whereas the ductility of Ag 2 TiGa and Ag 2 TiTl was better than that of Ag 2 VGa.The spin density of states of Ag 2 VGa has evident spin splitting near the Fermi level,and the total magnetic moment of the Ag 2 VGa structure is 2.28μB,which indicates that Ag 2 VGa is magnetic.These studies enrich research on Ag-based Heusler alloys and provide theoretical references for subsequent theoretical and experimental research.展开更多
In present work,the effect of Ge substitution for Mn on crystal structure and martensitic transformation was carefully investigated in magnetic shape memory Ni_(50)Mn _(36-x)Ge_(x)Sn_(14)(x=0,1) alloys.From X-ray diff...In present work,the effect of Ge substitution for Mn on crystal structure and martensitic transformation was carefully investigated in magnetic shape memory Ni_(50)Mn _(36-x)Ge_(x)Sn_(14)(x=0,1) alloys.From X-ray diffraction(XRD) patterns,it can be found that each sample possesses cubic austenitic structure(L21) at room temperature and the main peak(220) shifts to higher degree with Ge doping,indicating that the cell volume of austenitic phase shrinks.With Ge content increasing,martensitic transformation(MT),temperature shifts to higher temperature region and the difference of magnetization between martensitic and austenitic phases(AM) also increases.In addition,the magnetocaloric effect(MCE) and phase transition strain(ΔL/L) were investigated in Ni50Mn35-GeSn14alloy.The maximal magnetic entropy change(ΔSm) associated with martensitic transition is 3.9 J·kg^(-1)-K^(-1)with applied magnetic field change of 5 T and the maximal ΔL/L reaches 0.18% in this alloy.展开更多
The structure of the all-d-metal alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x=0–50)is investigated by using theoretical and experimental methods.The first-principles calculations indicate that the most stable structure of th...The structure of the all-d-metal alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x=0–50)is investigated by using theoretical and experimental methods.The first-principles calculations indicate that the most stable structure of the Ni_2MnV alloy is face-centered cubic (fcc)type structure with ferrimagnetic state and the equilibrium lattice constant is 3.60A,which is in agreement with the experimental result.It is remarkable that replacing partial Ni with Co can turn the alloy from the fcc structure to the B2-type Heusler structure as Co content x>37 by using the melting spinning method,implying that the d–d hybridization between Co/Mn elements and low-valent elements V stabilizes the Heusler structure.The Curie temperature T_(C) of all-dmetal Heuser alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x>37)increases almost linearly with the increase of Co due to that the interaction of Co–Mn is stronger than that of Ni–Mn.A magnetic transition from ferromagnetic state to weak magnetic state accompanying with grinding stress induced transformation from B2 to the dual-phase of B2 and fcc has been observed in these all-d-metal Heusler alloys.This phase transformation and magnetic change provide a guide to overcome the brittleness and make the all-d-metal Heusler alloy interesting in stress and magnetic driving structural transition.展开更多
Brittleness is a critical issue hindering the potential application of the X_2YZ-type full Heusler alloys in several fields of state-of-the-art technologies.To realize optimization of brittleness or design a ductile H...Brittleness is a critical issue hindering the potential application of the X_2YZ-type full Heusler alloys in several fields of state-of-the-art technologies.To realize optimization of brittleness or design a ductile Heuser alloy,it is greatly urgent to identify the key materials factors deciding brittleness and establish an empirical rule to effectively evaluate ductility.For this purpose,by using a machine learning and human analysis cooperation approach,the brittleness of the X_2YZ-type Heusler alloys was systematically studied.Results showed that the ductility is majorly decided by 6 key materials factors in the studied alloys.Using these 6 factors,a machine learning model to predict the Pugh's ratio k was constructed.Further analyses showed that the crystal structure of the X component could be the most critical factor deciding the ductility.The X component has the face-centered cubic(FCC)structure for most of the alloys with superior ductility.To effectively estimate ductility and guide materials design,an empirical formula of k=mEWF_(m+n)G_(m)+k_(0)was established based on the known information of electron work function(EWF)and shear modulus(G)of the X,Y,and Z elements where the subscript m represents the weight-average value.The coefficients of m(negative)and n(positive)were confirmed to have opposite signs,which can be explained based on the relations between the ductility and the deformation/fracture resistance.This work is expected to deepen the understanding in ductility and promote the design of advanced ductile Heusler alloys.展开更多
Using the first-principles calculations,we study the structural,electronic,and magnetic properties along with exchange interactions and Curie temperatures for CrZrCoZ(Z=Al,Ga,In,Tl,Si,Pb)quaternary Heusler alloys.The ...Using the first-principles calculations,we study the structural,electronic,and magnetic properties along with exchange interactions and Curie temperatures for CrZrCoZ(Z=Al,Ga,In,Tl,Si,Pb)quaternary Heusler alloys.The results show that the CrZrCoZ alloys are half-metallic ferrimagnets,and their total spin magnetic moments,which are mainly carried by the Cr atom,obey the Slater-Pauling rule.Analysis of local density of states confirms that the exchange splitting between eg and t2g states leads to the formation of half-metallic gap.According to the calculated Heisenberg exchange coupling parameters,it is found that the Cr(A)-Cr(A)and Cr(A)-Zr(B)exchanges dominate the appearance of ferrimagnetic states in CrZrCoZ(Z=Al,Ga,In,Tl,Pb)alloys,and it is the Cr(A)-Zr(B)and Zr(B)-Zr(B)exchanges for CrZrCoSi alloy.Finally,we estimate the Curie temperatures of CrZrCoZ by using mean-field approximation,it is found that the CrZrCoZ(Z=Al,Ga,In,Tl,Pb)alloys have noticeably higher Curie temperatures than room temperature.So,we expect that the CrZrCoZ alloys are promising candidates in spintronic applications in future.展开更多
In this work, pronounced oscillations in the time-resolved reflectivity of Heusler alloy Co2MnAl films which are epitaxially grown on Ga As substrates are observed and investigated as a function of film thickness, pro...In this work, pronounced oscillations in the time-resolved reflectivity of Heusler alloy Co2MnAl films which are epitaxially grown on Ga As substrates are observed and investigated as a function of film thickness, probe wavelength,external magnetic field and temperature. Our results suggest that the oscillation response at 24.5 GHz results from the coherent phonon generation in Co2MnAl film and can be explained by a propagating strain pulse model. From the probe wavelength dependent oscillation frequency, a sound velocity of(3.85±0.1)×10-3m/s at 800 nm for the epitaxial Co2MnAl film is determined at room temperature. The detected coherent acoustic phonon generation in Co2MnAl reported in this work provides a valuable reference for exploring the high-speed magnetization manipulation via magnetoelastic coupling for future spintronic devices based on Heusler alloy films.展开更多
This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis whe...This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they trans-form from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.展开更多
We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn(50)Ni(40)Sn(10-x)Sbx(x = 1, 2, 3, and 4) alloys. All the prepared samples exhibit a B2-type structure...We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn(50)Ni(40)Sn(10-x)Sbx(x = 1, 2, 3, and 4) alloys. All the prepared samples exhibit a B2-type structure with the space group F m3 m at room temperature. The substitution of Sb increases the valence electron concentration and decreases the unit cell volume. As a result, the magnetostructural transformation shifts rapidly towards higher temperatures as x increases.The changes in magnetic entropy under different magnetic field variations are explored around this transformation. The isothermal magnetization curves exhibit typical metamagnetic behavior, indicating that the magnetostructural transformation can be induced by a magnetic field. The tunable martensitic transformation and magnetic entropy changes suggest that Mn(50)Ni(40)Sn(10-x)Sbx alloys are attractive candidates for applications in solid-state refrigeration.展开更多
The effects of the addition of Co on the martensitic transformation and Curie transition temperatures of polycrystalline Ni46-xCu4CoxMn33.sGa16.5 (x = 0, 1, 3, 5) alloys are investigated. An abrupt decrease in the m...The effects of the addition of Co on the martensitic transformation and Curie transition temperatures of polycrystalline Ni46-xCu4CoxMn33.sGa16.5 (x = 0, 1, 3, 5) alloys are investigated. An abrupt decrease in the martensitic transformation temperature and an obvious increase in the Curie transition temperature of austenite (TA) are observed when Co is doped in the NiCuMnGa alloy. As a result, the composition range for obtaining the magnetostructural transition is extended. Furthermore, the effect of a strong magnetic field on the magnetostructural transition is analyzed. This study offers a possible method to extend the composition range for obtaining magnetostructural transition in Heusler alloys.展开更多
The Co2FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample posi...The Co2FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe (1 Oe = 79.5775 A.m ^-1), and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.展开更多
Using density functional theory calculations, we investigate the tetragonal distortion, electronic structure and magnetic property of Pt2MnSn. The results indicate that, when the volume-conserving tetragonal distortio...Using density functional theory calculations, we investigate the tetragonal distortion, electronic structure and magnetic property of Pt2MnSn. The results indicate that, when the volume-conserving tetragonal distortion occurs, the energy minimum appears at c/a = 0.84, and the energy difference between the minimum and cubic phase is as high as 107 me V/f. u. Thus from the point of view of thermodynamics, martensitie transformation may occur in Pt2MnSn with decreasing the temperature. The electronic structure of its cubic and martensitic phases also approves this. Moreover, both the cubic and tetragonal phases of Pt2MnSn are ferromagnetic structures and their total magnetic moments are 4.26 μB and 4.12 μB, respectively.展开更多
The half-metallic Heusler alloy CO_(2)FeSi is an ideal material in spintronic devices due to its higher spin polarization,higher Curie temperature and lower damping parameters.In this work,the dynamic magnetism of CO_...The half-metallic Heusler alloy CO_(2)FeSi is an ideal material in spintronic devices due to its higher spin polarization,higher Curie temperature and lower damping parameters.In this work,the dynamic magnetism of CO_(2)FeSi is modulated by electric field and it is demonstrated that the charge-spin conversion efficiencyξis continuous and controllable by the electric field.We further find an extremely highξin ferromagnetic/ferroelectric(FM/FE)heterostructures,which could be ascribed to interfacial effect in FM/FE interface.Moreover,we investigate that the charge-spin conversion efficiency varies with the electric field in a butterfly-like behavior,which accords with the S–E curve of Pb(Mg_(1/3)Nb_(2/3))O_3-Pb_(0.7)Ti_(0.3)O_(3)(PMN-PT)and could be attributed to strain effect.The modulation of charge-spin conversion efficiency in FM/FE heterostructures via electric field presents a profound potential for next-generation spintronic devices and applications of current-induced magnetization switching.展开更多
Magnetic shape memory alloys(MSMAs), both in condensed matter physics and in material science, are one of the most extensive research subjects. They show prompt response to the external magnetic field and give rise to...Magnetic shape memory alloys(MSMAs), both in condensed matter physics and in material science, are one of the most extensive research subjects. They show prompt response to the external magnetic field and give rise to large strain and have fine reversibility. The well-known example is Heusler-type MSMAs, which possess excellent multifunctional properties and have potential applications in energy transducer, actuator, sensor, microelectromechanical system, and magnetic refrigerator. In this paper, it is shown the recent progress in magnetostructural transformation, magnetic properties, shape deformation, magnetocaloric effect as well as magnetic field-induced shape memory effect in Ni–Mn–Ga, Ni Mn Z(Z = In, Sn, Sb),and Ni Co Mn Z(Z = In, Sn, Sb, Al) Heusler-type MSMAs.The remaining issues and possible challenges are briefly discussed.展开更多
Highly textured Heusler alloy Mn_(46)Ni_(42)Sn_(11)Sb_1 ribbons were prepared by melt spinning. The annealed high Mn content Mn46Ni42Sn11Sb1 ribbon cross-section microstructure, crystal structure, martensitic tr...Highly textured Heusler alloy Mn_(46)Ni_(42)Sn_(11)Sb_1 ribbons were prepared by melt spinning. The annealed high Mn content Mn46Ni42Sn11Sb1 ribbon cross-section microstructure, crystal structure, martensitic transformation(MT), and magnetoresistance(MR) properties were investigated. The MR in the annealed ribbon was assessed by the magnetic field direction perpendicular to the ribbon surface with the magnetic field up to 30 k Oe. The large negative value of 25% for MR was obtained at 244 K. The exchange bias(EB) effects of the as-spun and annealed ribbons were investigated. After annealing, the EB effects have been improved by about 25 Oe at the temperature of 50 K. The magnetizations have increased approximately by 10% more than the as-spun ribbon.展开更多
Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode (LED) has been detected at the transition of e–A0 C , where injected spin-polarized electrons recombine with bou...Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode (LED) has been detected at the transition of e–A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p + -GaAs layer. The large volume of the p + -GaAs layer can facilitate the detection of weak electric luminescence (EL) from e–A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p+ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron–hole exchange scattering (BAP mechanism), the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51271196,11274357,and 51021061)the Key Research Program of the Chinese Academy of Sciences+1 种基金the National Basic Research Program of China (Grant No. 2010CB833102)the Hi-Tech Research and Development Program of China (Grant No. 2011AA03A404)
文摘Our recent progress on magnetic entropy change(S) involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and austenite exhibit ferromagnetic(FM) behavior but show different magnetic anisotropies,a positive S as large as 4.1 J·kg^-1·K^-1 under a field change of 0-0.9 T was first observed at martensitic transition temperature T M~197 K.Through adjusting the Ni:Mn:Ga ratio to affect valence electron concentration e/a,T M was successfully tuned to room temperature,and a large negative S was observed in a single crystal.The △S attained 18.0 J·kg^-1·K^-1 under a field change of 0-5 T.We also focused on the metamagnetic alloys that show mechanisms different from the conventional ones.It was found that post-annealing in suitable conditions or introducing interstitial H atoms can shift the T M across a wide temperature range while retaining the strong metamagnetic behavior,and hence,retaining large magnetocaloric effect(MCE) and magnetoresistance(MR).The melt-spun technique can disorder atoms and make the ribbons display a B2 structure,but the metamagnetic behavior,as well as the MCE,becomes weak due to the enhanced saturated magnetization of martensites.We also studied the effect of Fe/Co co-doping in Ni 45(Co1-xFex)5 Mn36.6In13.4 metamagnetic alloys.Introduction of Fe atoms can assist the conversion of the Mn-Mn coupling from antiferromagnetic to ferromagnetic,thus maintaining the strong metamagnetic behavior and large MCE and MR.Furthermore,a small thermal hysteresis but significant magnetic hysteresis was observed around TM in Ni51Mn49-xInx metamagnetic systems,which must be related to different nucleation mechanisms of structural transition under different external perturbations.
基金supported by the Science Foundation of Surface Physics Laboratory (National Key Laboratory) of Fudan University (Grant No. FDS2008-B01)the Graduate Innovation Foundation of Shanghai University (Grant Nos. SHUCX101065 and SHUCX102011)the National Natural Science Foundation of China (Grant Nos. 50932003 and 10804068)
文摘This paper presents a study of the inverse magnetocaloric effect (MCE) corresponding to martensitic transition using various experimental approaches for Ni46Cu4Mn38Sn12 and NisoCoMn34In]5 Heusler alloy. Through heat capacity measurements, it is found that the "giant inverse MCE" upon martensitic transition evaluated by the Maxwell relation in these alloys are unphysical results. This is due to the coexistence of both martensitic and austenitic phases, as well as thermal hysteresis during martensitic transition. However, careful study indicates that the spurious results during martensitic transition can be removed using a Clausius Clapeyron equation based on magnetization measurements.
基金Project supported by the Chongqing City Funds for Distinguished Young ScientistsChina(Grant No.cstc2014jcyjjq50003)+5 种基金the Basic and Frontier Research Project of Chongqing CityChina(Grant No.cstc2013jj B50001)the Project of Chongqing Normal UniversityChina(Grant No.13XLB030)the Project of Scientific Research for High Level Talent in Colleges and Universities of Hebei ProvinceChina(Grant No.GCC2014042)
文摘The total energy, electronic structures, and magnetisms of the Al Cu2Mn-type Co2TiSb1-xSnx(x = 0, 0.25, 0.5) with the different lattice parameter ratios of c/a are studied by using the first-principles calculations. It is found that the phase transformation from the cubic to the tetragonal structure lowers the total energy, indicating that the martensitic phase is more stable and that a phase transition from austenite to martensite may happen at a lower temperature. Thus, a ferromagnetic shape memory effect can be expected to occur in these alloys. The Al Cu2Mn-type Co2TiSb1-xSnx(x = 0, 0.25, 0.5) alloys are weak ferrimagnets in the austenitic phase and martensitic phase.
基金financially supported by the Key Project of Natural Science Foundation of Jiangxi Province(No.20192ACB20004)the National Natural Science Foundation of China(No.51671097)the Open Project awarded by National Key Laboratory State Microstructures Physics(No.M32037)。
文摘Nowadays,searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields,such as solid-state refrigeration,magnetic actuators,magnetic sensors and intelligent/smart devices.In this work,the magnetic-field-induced metamagnetic reverse martensitic transformation(MFIRMT)from paramagnetic martensite to ferromagnetic austenite with multiple magneto-responsive effects is realized in Fe-doped Co-V-Ga Heusler alloys by manipulating the magnetic ordering.The martensitic transformation temperature Tmreduces quasi-linearly with increasing Fe-content.In strikingly contrast with the Fe-free alloys,the magnetization difference(M')across martensitic transformation increases by three orders of magnitude for Fe-doped alloys.The increased M'should be ascribed to the reduction of Tm,almost unchanged Curie temperature of austenite and the increased magnetic moment in the samples with higher Fe-content.The large M'provides strong driving force to realize the MFIRMT and accordingly multiple magneto-responsive effects,such as magnetocaloric,magnetoresistance and magnetostriction effects.Meanwhile,giant Vickers hardness of 518 HV and compressive strength of 1423 MPa are achieved.Multiple magneto-responsive effects with exceptional mechanical properties make these alloys great potential candidates for applications in many fields.
基金financially supported by the National Natural Science Foundation of China(No.51771044)the Natural Science Foundation of Hebei Province(No.E2019501061)+3 种基金the Performance subsidy fund for Key Laboratory of Dielectric and Electrolyte Functional Material Hebei Province(No.22567627H)the Fundamental Research Funds for the Central Universities(No.N2223025)the State Key Lab of Advanced Metals and Materials(No.2022-Z02)Programme of Introducing Talents of Discipline Innovation to Universities 2.0(the 111 Project of China 2.0,No.BP0719037)。
文摘The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125,0.25,0.375,y=0.625)]alloys were systematically studied by the first-principles calculations.For the formation energy,the martensite is smaller than the austenite,the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation.The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) (y<0.625) alloys.When y=0.625 in the Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) series,the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state.Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy.Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance,but reduce the toughness in the Ni–Mn–Cu–Ti alloy.And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys.The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.
基金This work was financially supported by the National Natural Sci-ence Foundation of China(Grant Nos.:11965005 and 11964026)the Natural Science Basic Research plan in Shaanxi Province of China(Grant Nos.:2020JM-186,2022JM-035,and 2022JQ-008)the Fundamen-tal Research Funds for the Central Universities.All the authors thank the computing facilities at High Performance Computing Center of Xidian University.
文摘There are various new structures with superior performance for Heusler alloy materials that are widely used in spintronic materials,thermoelectric materials,and other fields.In this study,three new Ag-based full-Heusler alloys(Ag 2 TiGa,Ag 2 VGa,and Ag 2 TiTl)are proposed.The stability,mechanical properties,and electronic proper-ties of these three new Ag-based Heusler alloys were studied using first-principles calculations.The results showed that the compression resistance,shear resistance,stiffness,and elastic anisotropy of Ag 2 VGa were greater than those of Ag 2 TiGa and Ag 2 TiTl,whereas the ductility of Ag 2 TiGa and Ag 2 TiTl was better than that of Ag 2 VGa.The spin density of states of Ag 2 VGa has evident spin splitting near the Fermi level,and the total magnetic moment of the Ag 2 VGa structure is 2.28μB,which indicates that Ag 2 VGa is magnetic.These studies enrich research on Ag-based Heusler alloys and provide theoretical references for subsequent theoretical and experimental research.
基金financially supported by the National Natural Science Foundation of China (Nos.51371111, 11364035 and 11404186)the Key Basic Research Program of Science and Technology Commission of Shanghai Municipality (No. 13JC1402400)+1 种基金the Project for Applied Basic Research Programs of Yunnan Province (No.2013FZ110)the Project for Innovation Research Team of Qujing Normal University (No.TD201301)
文摘In present work,the effect of Ge substitution for Mn on crystal structure and martensitic transformation was carefully investigated in magnetic shape memory Ni_(50)Mn _(36-x)Ge_(x)Sn_(14)(x=0,1) alloys.From X-ray diffraction(XRD) patterns,it can be found that each sample possesses cubic austenitic structure(L21) at room temperature and the main peak(220) shifts to higher degree with Ge doping,indicating that the cell volume of austenitic phase shrinks.With Ge content increasing,martensitic transformation(MT),temperature shifts to higher temperature region and the difference of magnetization between martensitic and austenitic phases(AM) also increases.In addition,the magnetocaloric effect(MCE) and phase transition strain(ΔL/L) were investigated in Ni50Mn35-GeSn14alloy.The maximal magnetic entropy change(ΔSm) associated with martensitic transition is 3.9 J·kg^(-1)-K^(-1)with applied magnetic field change of 5 T and the maximal ΔL/L reaches 0.18% in this alloy.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51671024 and 52088101)State Key Lab of Advanced Metals and Materials(Grant No.2019Z12)the Fundamental Research Funds for the Central Universities(Grant No.FRF-BD-20-12A)。
文摘The structure of the all-d-metal alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x=0–50)is investigated by using theoretical and experimental methods.The first-principles calculations indicate that the most stable structure of the Ni_2MnV alloy is face-centered cubic (fcc)type structure with ferrimagnetic state and the equilibrium lattice constant is 3.60A,which is in agreement with the experimental result.It is remarkable that replacing partial Ni with Co can turn the alloy from the fcc structure to the B2-type Heusler structure as Co content x>37 by using the melting spinning method,implying that the d–d hybridization between Co/Mn elements and low-valent elements V stabilizes the Heusler structure.The Curie temperature T_(C) of all-dmetal Heuser alloy Ni_(50-x)Co_(x)Mn_(25)V_(25)(x>37)increases almost linearly with the increase of Co due to that the interaction of Co–Mn is stronger than that of Ni–Mn.A magnetic transition from ferromagnetic state to weak magnetic state accompanying with grinding stress induced transformation from B2 to the dual-phase of B2 and fcc has been observed in these all-d-metal Heusler alloys.This phase transformation and magnetic change provide a guide to overcome the brittleness and make the all-d-metal Heusler alloy interesting in stress and magnetic driving structural transition.
基金financially supported by the National Natural Science Foundation of China(Nos.51801020,51922026,51975111)the Fundamental Research Funds for the Central Universities(Nos.N2002005,N2105001)the 111 Project of China(Nos.BP0719037,B20029)。
文摘Brittleness is a critical issue hindering the potential application of the X_2YZ-type full Heusler alloys in several fields of state-of-the-art technologies.To realize optimization of brittleness or design a ductile Heuser alloy,it is greatly urgent to identify the key materials factors deciding brittleness and establish an empirical rule to effectively evaluate ductility.For this purpose,by using a machine learning and human analysis cooperation approach,the brittleness of the X_2YZ-type Heusler alloys was systematically studied.Results showed that the ductility is majorly decided by 6 key materials factors in the studied alloys.Using these 6 factors,a machine learning model to predict the Pugh's ratio k was constructed.Further analyses showed that the crystal structure of the X component could be the most critical factor deciding the ductility.The X component has the face-centered cubic(FCC)structure for most of the alloys with superior ductility.To effectively estimate ductility and guide materials design,an empirical formula of k=mEWF_(m+n)G_(m)+k_(0)was established based on the known information of electron work function(EWF)and shear modulus(G)of the X,Y,and Z elements where the subscript m represents the weight-average value.The coefficients of m(negative)and n(positive)were confirmed to have opposite signs,which can be explained based on the relations between the ductility and the deformation/fracture resistance.This work is expected to deepen the understanding in ductility and promote the design of advanced ductile Heusler alloys.
基金Project supported by the National Natural Science Foundation of China(Grant No.11864021)Foundation of A Hundred Youth Talents Training Program of Lanzhou Jiaotong University,China,the Key Talent Foundation of Gansu Province,China(Grant No.2020RCXM100)Excellent Research Team of Lanzhou Jiaotong University,China(Grant No.201803).
文摘Using the first-principles calculations,we study the structural,electronic,and magnetic properties along with exchange interactions and Curie temperatures for CrZrCoZ(Z=Al,Ga,In,Tl,Si,Pb)quaternary Heusler alloys.The results show that the CrZrCoZ alloys are half-metallic ferrimagnets,and their total spin magnetic moments,which are mainly carried by the Cr atom,obey the Slater-Pauling rule.Analysis of local density of states confirms that the exchange splitting between eg and t2g states leads to the formation of half-metallic gap.According to the calculated Heisenberg exchange coupling parameters,it is found that the Cr(A)-Cr(A)and Cr(A)-Zr(B)exchanges dominate the appearance of ferrimagnetic states in CrZrCoZ(Z=Al,Ga,In,Tl,Pb)alloys,and it is the Cr(A)-Zr(B)and Zr(B)-Zr(B)exchanges for CrZrCoSi alloy.Finally,we estimate the Curie temperatures of CrZrCoZ by using mean-field approximation,it is found that the CrZrCoZ(Z=Al,Ga,In,Tl,Pb)alloys have noticeably higher Curie temperatures than room temperature.So,we expect that the CrZrCoZ alloys are promising candidates in spintronic applications in future.
基金supported by the National Basic Research Program of China(Grant No.2013CB922303)the National Natural Science Foundation of China(Grant No.61334006)
文摘In this work, pronounced oscillations in the time-resolved reflectivity of Heusler alloy Co2MnAl films which are epitaxially grown on Ga As substrates are observed and investigated as a function of film thickness, probe wavelength,external magnetic field and temperature. Our results suggest that the oscillation response at 24.5 GHz results from the coherent phonon generation in Co2MnAl film and can be explained by a propagating strain pulse model. From the probe wavelength dependent oscillation frequency, a sound velocity of(3.85±0.1)×10-3m/s at 800 nm for the epitaxial Co2MnAl film is determined at room temperature. The detected coherent acoustic phonon generation in Co2MnAl reported in this work provides a valuable reference for exploring the high-speed magnetization manipulation via magnetoelastic coupling for future spintronic devices based on Heusler alloy films.
基金supported by the National Basic Research Program of China (Grant No.2006CB601101)the National High Technology Research and Development Program of China (Grant No.2007AA03Z440)the National Natural Science Foundation of China(Grant No.50731007)
文摘This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they trans-form from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.
基金supported by the National Natural Science Foundation of China(Grant Nos.51271093,51571121,11604148,and 51601092)the Fundamental Research Funds for the Central Universities,China(Grant Nos.30920140111010,30916011344,and 30916011345)+4 种基金Jiangsu Natural Science Foundation for Distinguished Young Scholars,China(Grant No.BK20140035)China Postdoctoral Science Foundation(Grant No.2016M591851)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK20160833 and BK20160829)Qing Lan Project,Six Talent Peaks Project in Jiangsu Province,Chinathe Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn(50)Ni(40)Sn(10-x)Sbx(x = 1, 2, 3, and 4) alloys. All the prepared samples exhibit a B2-type structure with the space group F m3 m at room temperature. The substitution of Sb increases the valence electron concentration and decreases the unit cell volume. As a result, the magnetostructural transformation shifts rapidly towards higher temperatures as x increases.The changes in magnetic entropy under different magnetic field variations are explored around this transformation. The isothermal magnetization curves exhibit typical metamagnetic behavior, indicating that the magnetostructural transformation can be induced by a magnetic field. The tunable martensitic transformation and magnetic entropy changes suggest that Mn(50)Ni(40)Sn(10-x)Sbx alloys are attractive candidates for applications in solid-state refrigeration.
基金supported by the National Natural Science Foundation of China(Grant Nos.50925101,512210163,and 51001004)the National Basic Research Program of China(973 Program)(Grant No.2012CB619404)+1 种基金the Natural Science Foundation of Beijing(Grant No.2132026)the Fundamental Research Funds for Central 212 Universities(Grant No.YWF-13-T-RSC-025)
文摘The effects of the addition of Co on the martensitic transformation and Curie transition temperatures of polycrystalline Ni46-xCu4CoxMn33.sGa16.5 (x = 0, 1, 3, 5) alloys are investigated. An abrupt decrease in the martensitic transformation temperature and an obvious increase in the Curie transition temperature of austenite (TA) are observed when Co is doped in the NiCuMnGa alloy. As a result, the composition range for obtaining the magnetostructural transition is extended. Furthermore, the effect of a strong magnetic field on the magnetostructural transition is analyzed. This study offers a possible method to extend the composition range for obtaining magnetostructural transition in Heusler alloys.
基金Project supported by the National Natural Science Foundation of China(Grant No.11074040)the Key Project of Department of Science and Technology of Shangdong Province of China(Grant No.ZR2012FZ006)
文摘The Co2FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe (1 Oe = 79.5775 A.m ^-1), and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51301119,51301195,51171206 and 51401140the National Science Foundation for Young Scientists of Shanxi Province under Grant No 2013021010-1the Youth Foundation of Taiyuan University of Technology under Grant No 1205-04020102
文摘Using density functional theory calculations, we investigate the tetragonal distortion, electronic structure and magnetic property of Pt2MnSn. The results indicate that, when the volume-conserving tetragonal distortion occurs, the energy minimum appears at c/a = 0.84, and the energy difference between the minimum and cubic phase is as high as 107 me V/f. u. Thus from the point of view of thermodynamics, martensitie transformation may occur in Pt2MnSn with decreasing the temperature. The electronic structure of its cubic and martensitic phases also approves this. Moreover, both the cubic and tetragonal phases of Pt2MnSn are ferromagnetic structures and their total magnetic moments are 4.26 μB and 4.12 μB, respectively.
基金the National Natural Science Foundation of China(Grant No.11974149)the Natural Science Foundation of Gansu Province(Grant No.21JR7RA472)。
文摘The half-metallic Heusler alloy CO_(2)FeSi is an ideal material in spintronic devices due to its higher spin polarization,higher Curie temperature and lower damping parameters.In this work,the dynamic magnetism of CO_(2)FeSi is modulated by electric field and it is demonstrated that the charge-spin conversion efficiencyξis continuous and controllable by the electric field.We further find an extremely highξin ferromagnetic/ferroelectric(FM/FE)heterostructures,which could be ascribed to interfacial effect in FM/FE interface.Moreover,we investigate that the charge-spin conversion efficiency varies with the electric field in a butterfly-like behavior,which accords with the S–E curve of Pb(Mg_(1/3)Nb_(2/3))O_3-Pb_(0.7)Ti_(0.3)O_(3)(PMN-PT)and could be attributed to strain effect.The modulation of charge-spin conversion efficiency in FM/FE heterostructures via electric field presents a profound potential for next-generation spintronic devices and applications of current-induced magnetization switching.
基金financially supported by the National Natural Science Foundation of China (Nos. 51371105, 51071023, and 51101047)
文摘Magnetic shape memory alloys(MSMAs), both in condensed matter physics and in material science, are one of the most extensive research subjects. They show prompt response to the external magnetic field and give rise to large strain and have fine reversibility. The well-known example is Heusler-type MSMAs, which possess excellent multifunctional properties and have potential applications in energy transducer, actuator, sensor, microelectromechanical system, and magnetic refrigerator. In this paper, it is shown the recent progress in magnetostructural transformation, magnetic properties, shape deformation, magnetocaloric effect as well as magnetic field-induced shape memory effect in Ni–Mn–Ga, Ni Mn Z(Z = In, Sn, Sb),and Ni Co Mn Z(Z = In, Sn, Sb, Al) Heusler-type MSMAs.The remaining issues and possible challenges are briefly discussed.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB722801)the Postdoctoral Science Foundation of China(Grant No.2015M571285)+3 种基金the National Natural Science Foundation of China(Grant No.51401140)the Postdoctoral Research Station Foundation of Taiyuan University of Science and Technology,China(Grant Nos.20142014,20152041,and 20151082)the Natural Science Foundation of Shanxi Province,China(Grants Nos.2015021019,2015091011,and 2015081011)the Key Team of Scientific and Technological Innovation of Shanxi Province,China(Grant No.2013131009)
文摘Highly textured Heusler alloy Mn_(46)Ni_(42)Sn_(11)Sb_1 ribbons were prepared by melt spinning. The annealed high Mn content Mn46Ni42Sn11Sb1 ribbon cross-section microstructure, crystal structure, martensitic transformation(MT), and magnetoresistance(MR) properties were investigated. The MR in the annealed ribbon was assessed by the magnetic field direction perpendicular to the ribbon surface with the magnetic field up to 30 k Oe. The large negative value of 25% for MR was obtained at 244 K. The exchange bias(EB) effects of the as-spun and annealed ribbons were investigated. After annealing, the EB effects have been improved by about 25 Oe at the temperature of 50 K. The magnetizations have increased approximately by 10% more than the as-spun ribbon.
基金Project supported by the National Basic Research Program of China (Grant No. 2011CB932901)the National Natural Science Foundation of China (GrantNo. 60836002)
文摘Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode (LED) has been detected at the transition of e–A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p + -GaAs layer. The large volume of the p + -GaAs layer can facilitate the detection of weak electric luminescence (EL) from e–A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p+ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron–hole exchange scattering (BAP mechanism), the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.