Search

Single-phase Mn50Ni40In10−xCux (x = 0, 1, 2, 4, 6, 8, and 10) Heusler alloys were synthesized by melt-spinning method. Martensitic transformation is retained within the whole composition range studied. The substitution of Cu for In leads to a drastic increase in the martensitic transformation temperature TM from below room temperature to above 750 K, and enhances the antiferromagnetic character of the martensite. The increase in TM is related to the increasing electron concentration e/a and decreasing cell volume V with Cu doping. The energy difference between martensite and austenite also increases with Cu doping, which tends to elevate the TM. Cu doping can enhance the metallic bonding character in NiMn-based magnetic shape memory alloys (MSMAs) and is a grain refining strategy of their ribbons. The oriented columnar grains in In-rich samples change to fine equiaxial grains in Cu-rich samples. All this has a positive effect on the strength and ductility. The tensile strength of the Mn50Ni40Cu10 ribbon is 3.6 times higher than that of Mn50Ni40In6Cu4. So, Mn–Ni–Cu can be a promising all-d-metal Heusler alloy platform for developing MSMAs with interesting properties. [ABSTRACT FROM AUTHOR]

Abstract The stable structure of Heusler alloy Ti 2 NiAl and its influence on the electronic structure and magnetic properties were investigated theoretically. It is found that in Ti 2 NiAl, the L2 1 and XA structures have similar stabilities, this is related to the competition between the "number of valence electrons" and atomic size effect. L2 1 B type structure can lower the total energy of Ti 2 NiAl further by 0.04eV/f.u. and has the highest stability, in which Ti and Ni atoms occupy the A, C sites randomly. The energy difference between L2 1 /XA and L2 1 B structures is about 0.04eV/f.u. Different atomic ordering influence the electronic structure obviously. XA type Ti 2 NiAl is a half-metal with an integral total moment of 3.00 μ B /f.u., as has been reported in literature. But this character is destroyed in both L2 1 and L2 1 B structures. In the stable L2 1 B structure, Ti 2 NiAl is a normal ferromagnetic metal with a total magnetic moment of 0.84 μ B /f.u. Highlights • Stability of different atomic in Heusler alloy Ti 2 NiAl was compared. • Stabilization effect of L2 1 B disorder on Ti 2 -based Heusler alloys was reported. • Ti 2 NiAl is not a half-metal under the most stable L2 1 B structure. [ABSTRACT FROM AUTHOR]

Fe 2 NiSi FCC phase has been prepared by ball-milling successfully, which is different from the BCC Heusler phase prepared by arc-melting in previous literatures. The FCC Fe 2 NiSi is a ferromagnet with a lattice constant of 3.58 Å. The phase stability of the FCC and BCC Fe 2 NiSi has been compared by first-principles calculations. It has been found that the FCC structure has a lower total energy compared with the highly-ordered Heusler structures XA and L2 1 , that is the reason why the FCC phase can be prepared by ball-milling. However, the Fe (A)–Ni (C) disorder in the BCC XA structure can lower its total energy further and make it smaller than the FCC phase. So the most stable structure in Fe 2 NiSi is L2 1 B, as has been observed in the arc-melting sample. This can be explained from their DOS structures. The calculated total moments for the FCC and BCC phases agree with their M s at 5 K quite well. [ABSTRACT FROM AUTHOR]

A competition between the conventional L2 1 ordering and inverse XA ordering has been observed in Heusler alloys X 2 CuAl (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni). In X 2 CuAl, the site preference of Cu is strongly influenced by the crystal structure of pure X elements. When X element has a close-packed FCC or HCP structure (Sc, Ti, Co and Ni), Cu prefers entering the ( 1 4 , 1 4 , 1 4 ) position and forms the L2 1 structure, but when X has a BCC structure (V, Cr, Mn, Fe), Cu prefers entering the ( 1 2 , 1 2 , 1 2 ) position and forms the XA structure. So the crystal structure of pure X element should also be considered together with number of valence electrons when discussing the site preference in Heusler alloys. Mn 2 CuAl is found to be a spin gapless semiconductor (SGS) with fully-compensated total moment. Based on this, a possible rule to design SGS has been discussed. Finally, X 2 CuAl alloys all have a negative formation energy except for V 2 CuAl and Cr 2 CuAl. [ABSTRACT FROM AUTHOR]

The martensitic transformation and electronic structure of Heusler alloys Mn 2 YIn (Y=Ni, Pd, Pt) have been investigated by both first-principles calculation and experimental investigation. Theoretical calculation reveals that, the energy difference Δ E between the tetragonal martensitic phase and cubic austenitic phase increases with Y varying from Ni to Pt in Mn 2 YIn. Thus a structural transition from cubic to tetragonal is most likely to happen in Heusler alloy Mn 2 PtIn. A single Heusler phase can be obtained in both Mn 2 PtIn and Mn 2 PdIn. A martensitic transformation temperature of 615 K has been identified in Mn 2 PtIn. And in Mn 2 PdIn, the austenitic phase is stable and no martensitic transformation is observed till 5 K. This indicates there may exist a positive relation between Δ E and martensitic transformation temperature. Calculated results show that Mn 2 YIn are all ferrimagnets in both austenitic and martensitic phases. The magnetic properties are mainly determined by the antiparallel aligned Mn spin moments. These findings can help to develop new FSMAs with novel properties. [ABSTRACT FROM AUTHOR]

The site preference of Cu does not follow the usual valence electrons rule in Ni 2 -based Heusler alloys Ni 2 CuSn and Ni 2 CuSb. The phase stabilities of three possible structures, namely L2 1 , XA and L2 1 B, have been compared. Among them L2 1 has the lowest total energy and is preferable, while L2 1 B has the highest energy. The energy differences between L2 1 and the other two structures are quite large. The high phase stability of the L2 1 structure is mainly related to the strong hybridization between the d states of Cu, Ni and the low N(E F ). Single phase, highly-ordered Ni 2 CuSn and Ni 2 CuSb samples have been prepared experimentally. The XRD patterns suggest that Ni 2 CuSn and Ni 2 CuSb do crystallize in the L2 1 structure, agreeing with the theoretical prediction. Finally, both of them have a paramagnetic ground state. [ABSTRACT FROM AUTHOR]

Heusler alloy Cr 2 CoGa with 24 valence electrons is a promising candidate for half-metallic completely compensated ferrimagnets. Its electronic structure and atomic disorder have been investigated by using a KKR–CPA method. The equilibrium lattice constant is 5.88 Å and the total moment is as small as 0.09 μ B . This near zero moment is mainly determined by the antiparallel aligned Cr (A) and Cr (B) spin moments, which are −2.16 μ B and 2.17 μ B , respectively and compensate each other. The calculated spin polarization ratio is as high as 95%. Three kinds of atomic disorder have been considered in Cr 2 CoGa: Cr (B)-Co, Cr (A)-Co and Cr (B)-Ga. Among them, Cr (A)-Co and especially Cr (B)-Co disorder raise the total energy obviously. While Cr (B)-Ga disorder decreases the total energy by ~0.14 eV. So Cr (B)-Ga disorder is more energetically favored in the sample. The influence of Cr (B)-Ga disorder on the magnetic moment and electronic structure is small. The total moment only increases slightly to 0.16 μ B . The influence of Cr (A)-Co disorder on the magnetic properties is also not obvious. Whereas Cr (B)-Co disorder increases the total moment obviously, which is mainly related to the ferromagnetic coupling between the Cr spin moments at A, C sites. [ABSTRACT FROM AUTHOR]

The site preference, electronic structure and magnetism of a newly discovered Heusler alloy Mn 2 RuSn have been investigated. The Hg 2 CuTi-type (XA) structure is found to be energetically favored in Mn 2 RuSn. Mn 2 RuSn is a normal ferrimagnetic metal at equilibrium lattice constant, but with 2% contraction of the lattice, it becomes a half-metal with a spin moment of 2μ B . A tetragonal martensitic transformation is predicted in Mn 2 RuSn. The total moment of the tetragonal phase is near zero, which results in a large Δ M between the saturation moments of martensite and austenite. Finally, in tetragonal Mn 2 RuSn, a high spin polarization ratio of 93% is predicted. These properties make Mn 2 RuSn a potential candidate for spintronics materials. [ABSTRACT FROM AUTHOR]

Abstract: The martensitic transformation in Heusler alloy Mn2PtIn has been investigated by first-principles calculations and experimental studies. Theoretical calculation reveals that, in Mn2PtIn, a transition from cubic structure to tetragonal one is favorable in energy. This has been confirmed by following experimental studies. At room temperature, Mn2PtIn crystallizes in a tetragonal structure of the space group I-4m2. And a transition from tetragonal to cubic Heusler phase occurs at 638K. Mn2PtIn is a ferrimagnet in both austenitic and martensitic phases. Its magnetic properties are mainly determined by the antiparallel aligned Mn spin moments. These findings can greatly enlarge our scope of discovering new FSMAs in Heusler alloys containing 4d and 5d elements. [Copyright &y& Elsevier]

Abstract: The electronic structure and magnetism of Heusler alloys Mn2NiGe and Ni2MnGe have been studied by first-principles calculations. The possible non-modulated tetragonal martensitic transformation in them has been predicted. For both Mn2NiGe and Ni2MnGe, the tetragonal martensitic phase is lower in energy compared with the cubic austenitic phase. In Ni2MnGe, the martensitic transformation follows the conservation of volume. But in Mn2NiGe, a small contraction of the martensitic cell volume is predicted. The energy difference ΔE between the martensitic and austenitic phase is −8 meV/cell in Ni2MnGe and −80 meV/cell in Mn2NiGe, so it is more likely to observe martensitic transformation in Mn2NiGe or Heusler alloys with similar compositions. Ni2MnGe is found to be a ferromagnet, while Mn2NiGe is a ferrimagnet in which the Mn spin moments are in antiparallel coupling. [Copyright &y& Elsevier]

Abstract: The electronic structure and magnetic properties of new Fe-based Heusler alloys Fe2TiZ (Z=Ga, Ge, As, In, Sn and Sb) have been studied by first-principles calculations. In these alloys, the 24-electron Fe2TiGe, Fe2TiSn are nonmagnetic semiconductors and other compounds are all ferrimagnetic metals. Fe2TiAs and Fe2TiSb are predicted to be half-metals with 100% spin polarization. The spin polarization ratio in Fe2TiGa and Fe2TiIn is also quite high. The calculated total moment for Fe2TiAs and Fe2TiSb is 1μB, which is mainly determined by the Fe partial moment. The half-metallicity of Fe2TiSb is stable under lattice distortion. The spin polarization of Fe2TiSb is found to be 100% for the lattice variation in a range of 5.6–6.1Å, which is attractive in practical applications. [Copyright &y& Elsevier]

Abstract: The magnetic properties and electronic structure of Mn2NiZ (Z=In, Sn, Sb) have been studied. The magnetic structure of these alloys is mainly determined by the main-group element Z instead of the distance between the Mn atoms. Electronic structure calculations suggest that Mn2NiIn and Mn2NiSn are both ferrimagnets with antiparallel alignment between the Mn moments. But this antiferromagnetic coupling is weakened by the increasing number of valence electrons of the Z atoms. When it comes to Mn2NiSb, a ferromagnetic coupling between the Mn atoms is observed. Mn2NiSn and Mn2NiSb have been synthesized successfully. Their M s at 5K agree well with the theoretical value. [Copyright &y& Elsevier]

• New Fe 2 V 1-x Ru x Si Heusler alloys have been synthesized. • Ru doping can significantly stabilize the ferromagnetic state in Fe 2 V 1-x Ru x Si. • Site preference of Ru in Fe 2 V 1-x Ru x Si was determined and the origin was discussed. • Electronic structure and magnetism of Fe 2 V 1-x Ru x Si were investigated. A series of Fe 2 V 1-x Ru x Si (x = 0.25, 0.5, 0.75, 1) Heusler alloys was synthesized and the atomic ordering, electronic structure and magnetic properties of them were investigated theoretically and experimentally. When substituting for V, the Ru atom shows a strong tendency to occupy the C site and drives Fe to the B site, which was confirmed by both structural optimization and XRD measurement. This preferable occupation is related to the enhanced bonding character when Ru entering C site and becoming the nearest neighbor of Si. This knowledge is useful for understanding the site preference of transition metal atoms in Heusler alloys. Ru-doping can stabilize the ferromagnetic state in Fe 2 V 1-x Ru x Si effectively. Both the Curie temperature T C and saturation magnetization M s increase monotonously with Ru-doping. The increase of M s mainly comes from the partial spin moment of Fe, which gets large rapidly with expanding lattice after Ru-doping. The doping of Ru tends to close the minority pseudogap at E F , so the DOS structure indicates a normal ferromagnetic metal character in Fe 2 V 1-x Ru x Si. [ABSTRACT FROM AUTHOR]

The electronic structure, atomic disorder and magnetic properties of the Heusler alloy Fe 2 MnGa have been investigated experimentally and theoretically. BCC Fe 2 MnGa ribbon samples were prepared. Experimentally, a saturation magnetic moment (3.68 μ B at 5 K) much larger than the theoretical value (2.04 μ B ) has been reported. First-principles calculations indicate that the difference is related to the Fe–Mn disorder between A, B sites, as can also be deduced from the XRD pattern. L2 1 type Fe 2 MnGa is a ferrimagnet with antiparallel Fe and Mn spin moments. However, when Fe–Mn disorder occurs, part of Mn moments will be parallel to Fe moments, and the Fe moments also clearly increase simultaneously. All this results in a total moment of 3.74 μ B , close to the experimental value. [ABSTRACT FROM AUTHOR]

• Decomposition occurs in as-spun Mn 50 Ni 40 In 10 ribbons when annealing above 690 K. • Annealing Mn 50 Ni 40 In 10 ribbons at 770 K leads to the formation of In-rich second phase concentrating on grain boundary. • Improper annealing affects the magnetic properties drastically and disturbs the magnetic shape memory effect in Mn 50 Ni 40 In 10. • Formation energy and decomposition energy reveal the decomposition tendency of Mn-Ni-In. The phase stability, decomposition and its influence on the martensitic transformation and magnetic properties of magnetic shape memory alloy (MSMA) Mn 50 Ni 40 In 10 melt-spun ribbons were investigated experimentally and theoretically. As-spun Mn 50 Ni 40 In 10 was fine single Heusler phase with pronounced martensitic and magnetic transition below room temperature. However, in differential scanning calorimetry measurement an exothermic peak at 690 K and an endothermic peak at 765 K is observed during the heating of as-spun ribbons. The two peaks correspond to the growing of the punctiform precipitates in the grain interiors and the formation of a large amount of grain boundary segregation, respectively. After annealing at 870 K, the ribbon samples decompose into a cubic In-rich phase at grain boundaries and In-poor 7 M−modulate martensitic phase in the matrix. After annealing at 690 K and above, the martensitic transformation below room temperature is strongly weakened. Annealing temperature also has obvious influence on the 5 and 300 K saturation magnetization M s of Mn 50 Ni 40 In 10. Theoretical calculations on Mn 2 Ni 1.5 In 0.5 (Mn 50 Ni 37.5 In 12.5) give a negative formation energy (-0.11 eV/ f.u.) and a positive decomposition energy (0.22 eV/f.u.), indicating that this alloy can be metastable and tends to decompose into Mn 2 NiIn cubic phase and NiMn martensite, agreeing with the experimental results qualitatively. [ABSTRACT FROM AUTHOR]

• Origin of the large saturate moment at 5 K in Fe 2 MnGe DO 19 phase was determined. • Phase stability of cubic and hexagonal Fe 2 MnGe was investigated. • "Why Fe 2 MnGe DO 19 phase is stable at room temperature" was discussed. • Information on electronic structure of Fe 2 MnGe DO 19 phase was presented. The electronic structure, phase stability and magnetic properties of cubic and hexagonal type Fe 2 MnGe were investigated and compared with the well-known Heusler alloy Fe 2 MnSi. Three different structures L2 1 , DO 3 and DO 19 were considered for them. In both alloys the cubic phase (L2 1 and DO 3) has a lower total energy comparing with the hexagonal DO 19 phase at 0 K. But in Fe 2 MnGe the energy difference between the DO 19 and L2 1 phases is much smaller than Fe 2 MnSi. The DO 3 disorder can lower the stability of the cubic phase further and make the total energies of hexagonal and cubic phases closer, this can help the DO 19 phase gain stability. Finally, in Fe 2 MnGe, the energy difference is 0.12 eV/f.u., much smaller than the 0.41 eV/f.u. in Fe 2 MnSi. That is the possible reason why Fe 2 MnGe DO 19 phase can be synthesized experimentally and Fe 2 MnSi cannot. L2 1 type Fe 2 MnGe is a half-metal with 100% spin polarization and has a total spin moment of 3μ B /f.u. The spin polarization ratio of DO 3 phase is also high. But for the DO 19 hexagonal phase, a normal ferromagnetic metal character is observed. The calculated total moment for DO 19 type Fe 2 MnGe is larger than 6μ B /f.u. This total moment comes mainly from the large and parallel coupled partial spin moments of Fe and Mn. [ABSTRACT FROM AUTHOR]

Abstract Mn-Ni-Co-Ti alloys are newly reported all-d-metal Heusler alloys with magnetic field induced martensitic transformation and large volume discontinuity. Here we investigated the electronic structure and magnetic structural transition in Mn 2 Ni 1.5 Ti 0.5 and Mn 2 Ni 1.25 Co 0.25 Ti 0.5 theoretically. In these alloys, the same number of Mn atoms enter D (0.75, 0.75, 0.75) site when extra Ni/Co substitute for Ti. Mn (D) spin moment is parallel to that of Mn at B (0.25, 0.25, 0.25) site in cubic austenitic phase but becomes antiparallel in tetragonal martensitic phase. Then during the martensitic transition, the total magnetic moment decreases obviously. Compared with Mn 2 Ni 1.5 Ti 0.5, the doping of Co in Mn 2 Ni 1.25 Co 0.25 Ti 0.5 can enlarge the energy difference between the antiparallel and parallel configurations of Mn (B) and Mn (D) moments and thus stabilize the ferromagnetic coupling between them in austenite. DOS structure and charge density difference reveal this is related to the strong d-d hybridization between Co-Mn nearest neighbors. That is the origin of the "FM activation effect" of Co-doping in literature. The "volume-conserving assumption" may need improvement in all-d-metal Heusler alloys. The lowest total energy for Mn 2 Ni 1.25 Co 0.25 Ti 0.5 martensitic was obtained when its cell volume is smaller than the equilibrium cell volume of the austenite. The predicted volume contraction is as large as 3.5% with a c/a ratio of 1.45. These results give reasonable explanations for existing experimental observations. Highlights • Magnetic structural transition in Mn 2 Ni 1.25 Co 0.25 Ti 0.5 Heusler alloy was studied. • "FM activation effect" of Co in austenitic Heusler alloys was discussed. • Large volume contraction was predicted in Mn 2 Ni 1.25 Co 0.25 Ti 0.5 with phase transition. • Experimental observations in literature received reasonable explanations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Electronic structure of quaternary Heusler alloys FeRuYZ was investigated. • New spin gapless semiconductors and half-metals were reported. • Rule between formation energy and mine group element Z was discussed. Abstract Phase stability, electronic structure and magnetic properties of the FeRu-based quaternary Heusler alloys, FeRuYZ (Y = Ti, V, Cr, Mn and Z = Al, Ga, In, Si, Ge, Sn), have been investigated theoretically. In one primitive unit cell, these alloys contain 24–26 valence electrons. The formation energy E f of FeRuYZ increases with increasing atomic number of Z when the Y or Z elements belong to the same group in the periodic table. And in the same period, group-IIIA Z element is not preferable for the stability of FeRuYZ compared with corresponding group-IVA element. This can be explained from the charge density difference. The 24-electron FeRu-based quaternary Heusler alloys are all paramagnets. Among them, FeRuTiSi (Ge, Sn) are all semiconductors with real band gap at the Fermi levels. These alloys may have potential applications as thermoelectric materials. High spin polarization ratio is observed in the 25-electron Heusler alloys, among which FeRuCrAl is predicted to have a 100% spin polarization ratio. The 26-electron FeRuCrSi is found to be a spin gapless semiconductor (SGS) with total spin moment of 2μ B. These materials can be interesting for the development of spintronic materials. The origin of SGS character in FeRuCrSi was discussed and compared with half-metallic Fe 2 CrSi, in which Ru and Fe are isoelectronic. These findings can help to design new SGSs in Heusler alloys. [ABSTRACT FROM AUTHOR]

• All-d-metal Heusler alloy Mn 2 PtTi is a promising new MSMA with high martensitic transformation temperature. • Large volume effect of 2.9% cell shrinkage occurs in Mn 2 PtTi during the martensitic transformation. • Electronic structure and magnetic properties of new all-d-metal Heusler alloys Mn 2 PtZ (Z = Sc, Ti and V) are investigated. The atomic ordering, electronic structure, magnetic properties and martensitic transformation of three new all-d-metal Heusler alloys Mn 2 PtZ (Z = Sc, Ti and V) have been investigated theoretically to discover new magnetic shape memory alloys (MSMAs). Depending on the different third transition metal element Z, Mn 2 PtSc and Mn 2 PtTi tend to form XA structure while Mn 2 PtV forms L2 1 structure. This difference is related to their DOS structures. Charge density difference calculations indicate enhanced d-d hybridization in these all-d-metal Heusler alloys. Mn 2 PtZ are all ferrimagnets with their Mn-Mn or Mn-V local spin moments antiparallel coupled. In these alloys, Mn 2 PtTi is a possible new MSMA with the energy difference ΔE M between the martensite and austenite as large as −262 meV/f.u., which indicates a high martensitic transformation temperature and is related to the Jahn-Teller effect in the electronic structure. A large volume effect of 2.9% cell shrinkage occurs during the martensitic transformation. All this makes Mn 2 PtTi a promising candidate for MSMAs with wide applications. [ABSTRACT FROM AUTHOR]

The equiatomic quaternary Heusler alloy FeRuCrSi was synthesized and its atomic ordering, magnetic properties and electronic structure were investigated experimentally and theoretically. The FeRuCrSi formed a single Heusler phase and had a lattice constant of 5.811 Å at room temperature. An L2 1 B-type disorder related to the random occupation of Fe and Ru at 4a and 4b sites was identified in the X-ray diffraction pattern. The Curie temperature of FeRuCrSi was 346 K and the saturation magnetization at 5 K was 1.84 μ B /f.u., which is smaller than the integral value of 2.00 μ B required for ideal spin gapless semiconductor character and is likely related to the L2 1 B-type disorder. First-principles calculations revealed that ordered FeRuCrSi with Y II -type structure had the lowest total energy at 0 K. However, the energy difference between it and the L2 1 B structure was only 0.09 eV/f.u., thus the L2 1 B disorder dominated in the experimental sample because of the enthalpy of mixing and the "freezing" of high-temperature disorder at room temperature. The Y II -type FeRuCrSi was a SGS with a half-metallic gap in the minority density of states (DOS) and a zero-width gap in the majority DOS. However, the L2 1 B-type disorder disturbed the SGS character by narrowing the two gaps. The total spin moment of ordered FeRuCrSi was 2.00 μ B /f.u., mainly determined by the antiparallel coupled Cr and Fe/Ru spin moments. However, the total moment was slightly reduced in L2 1 B-type FeRuCrSi. All this suggests that the possible L2 1 B disorder should be carefully considered when designing and synthesizing half-metals/SGS in Heusler alloys for spintronic applications. • Equiatomic quaternary Heusler alloy FeRuCrSi was synthesized successfully, which is a ferrimagnet with T C of 346 K and Ms at 5 K of 1.84 μ B /f.u. • FeRuCrSi experimental sample crystallizes in a partly disordered L2 1 B structure • L2 1 B disorder disturbs the spin gapless semiconductor character predicted in literature • Influence of L2 1 B disorder should be considered carefully in the design of Heusler alloys for spintronic applications [ABSTRACT FROM AUTHOR]

Two new all-d-metal Heusler alloys Mn 2 Ni 1.5 Sc 0.5 and Ni 2 Mn 1.5 Sc 0.5 are proposed as candidates for magnetic shape memory alloys. In these alloys, the Sc atom prefers occupying the D (0.75, 0.75, 0.75) sites in the Heusler alloy lattice and forms d–d hybridization with its nearest neighbor atoms such as Ni. Martensitic transformation is possible in both Mn 2 Ni 1.5 Sc 0.5 and Ni 2 Mn 1.5 Sc 0.5. Differing from the "volume-conserving" character in classic Heusler alloys, a large volume shrinkage of 2.3% and 2.8% occurs in Mn 2 Ni 1.5 Sc 0.5 and Ni 2 Mn 1.5 Sc 0.5 during the martensitic transformation, respectively. The magnetization difference between the austenite and martensite is as large as 4.50 μ B /f.u. for Mn 2 Ni 1.5 Sc 0.5 and 4.49 μ B /f.u. for Ni 2 Mn 1.5 Sc 0.5 , due to the ferromagnetic–antiferromagnetic magnetic transition coupling with the martensitic transformation. The parallel coupled Mn (B) and Mn (D) spin moments in the austenite become antiparallel in the martensite, which leads to the large decrease of magnetization after the martensitic transformation. The energy difference ΔE M between the martensite and austenite is −45.5 and −25.9 meV/f.u. for Mn 2 Ni 1.5 Sc 0.5 and Ni 2 Mn 1.5 Sc 0.5 , respectively. The large ΔE M of Mn 2 Ni 1.5 Sc 0.5 derives from the strong Jahn–Teller effect in its density of states structure and makes it a promising candidate for magnetic shape memory alloys. • New possible all-d-metal MSMAs Mn 2 Ni 1.5 Sc 0.5 and Ni 2 Mn 1.5 Sc 0.5 basing on Sc element have been proposed • Large volume effect is observed during the martensitic transformation in Mn 2 Ni 1.5 Sc 0.5 and Ni 2 Mn 1.5 Sc 0.5 • Mn 2 Ni 1.5 Sc 0.5 can be a promising MSMA with metamagnetic martensitic phase transition and large volume change [ABSTRACT FROM AUTHOR]

Transition metal Zn shows a main group element-like behavior in Heusler alloys Ni 2 MnGa 1−x Zn x (x = 0, 0.25, 0.50, 075 and 1.00). Zn enters Ga (D) site when it substitutes for Ga in Ni 2 MnGa chemically. The equilibrium lattice constant decreases with increasing Zn content. But at the same time the magnetic properties do not change too much. Mn partial moment contributes most to the total moment and couples parallel to that of Ni in both austenite and martensite. The partly substitution of Zn for Ga can lead to an increase of martensitic transition temperature due to the competition between cell volume effect and valence electron concentration e/a. Accordingly, the largest energy difference ΔE M between the austenite and martensite was found when x = 0.5. This was further explained based on the electronic structure from the Jahn-Teller effect. Then Zn-doping can be used as a possible way to adjust the phase transition temperatures in Heusler type MSMAs. Zn is much cheaper than Ga or In, this can be quite meaningful for the development of high performance and low cost MSMAs and broaden their industrial applications. [ABSTRACT FROM AUTHOR]

The site preference, electronic structure, magnetic properties and martensitic transformation of all-d-metal Heusler alloys Zn 2 YMn (Y = Fe, Co, Ni, Cu) have been investigated by first-principles calculations. In these alloys L2 1 structure is found to be more stable compared with XA, in which two Zn atoms prefer occupying the equilibrium A, C sites in the lattice. The total spin moments of Zn 2 YMn are all larger than 3μ B and mainly come from the contribution of Mn. The contributions from Zn atoms are small for its low-lying d states, which do not hybridize with the d states of other atoms directly. Further calculation reveals that the tetragonal martensitic type Zn 2 YMn (Y = Fe, Co, Ni) can relax the total energy and are more stable than the cubic phase. The energy difference ΔE M between the cubic austenite and tetragonal martensite is as high as 0.31 eV in Zn 2 FeMn and decreases as Y atom varies from Fe to Ni. In martensitic type Zn 2 FeMn and Zn 2 CoMn, a quite large c/a ratio is observed, which is preferable for transformation strain effect. [ABSTRACT FROM AUTHOR]

BCC Heusler phase Ni 2 CoSi has been predicted to be a promising candidate to realize magnetic field induced martensitic transformation. We tried to prepare Ni 2 CoSi single phase using different methods. Single phase Ni 2 CoSi cannot be synthesized by arc-melting and annealing. Then we used mechanical alloying method to synthesize Ni 2 CoSi. But a FCC phase rather than BCC was obtained after ball-milling. The lattice constant of FCC Ni 2 CoSi is 3.52 Å and the Curie temperature is around 900 K. The saturation magnetization at 5 K is 2.44μ B /f.u. This FCC phase is stable and no transition is observed when heating to 1173 K. The electronic structure and phase stability of the FCC and BCC Heusler phase have been investigated by first-principles calculations. The FCC Ni 2 CoSi has lower total energy compared with BCC, agreeing with the experimental observation. But the calculated total moment is much smaller than the M s at 5 K. This difference is related to the atomic disorder and was discussed by KKR-CPA calculation. [ABSTRACT FROM AUTHOR]

Heusler alloy Co 2 RuSi has been synthesized by melt-spinning technology successfully. Co 2 RuSi bulk sample after annealing is composed of an HCP Co-rich phase and a BCC Ru-Si phase, but melt-spinning can suppress the precipitation of the HCP phase and produce a single Co 2 RuSi Heusler phase. In the XRD pattern, it is found that Ru has a strong preference for the (A, C) sites, though it has fewer valence electrons compared with Co. This site preference is different from the case in Heusler alloys containing only 3d elements and is supported further by first-principles calculations. Melt-spun Co 2 RuSi has a M s of 2.67 μ B /f.u. at 5 K and a Tc of 491 K. An exothermic peak is observed at 871 K in the DTA curve, corresponding to the decomposition of the Heusler phase. Finally, the site preference and magnetic properties of Co 2 RuSi were discussed based on electronic structure calculation and charge density difference. [ABSTRACT FROM AUTHOR]

The site preference of 4d transition metal element Zr in Heusler alloys Zr 2 YAl (Y = Cr, Mn, Fe, Co, Ni) has been investigated theoretically. In these alloys the two Zr atoms prefer entering the A (0, 0, 0) and C (0.5, 0.5, 0.5) sites in the lattice of Heusler alloys and forming L2 1 structure (Cu 2 MnAl-type). This is different from previous predictions based on “number of valence electrons”, in which Zr atoms were predicted to occupy A (0, 0, 0) and B (0.25, 0.25, 0.25) sites and form XA (Hg 2 CuTi-type) structure. Present work suggests that L2 1 structure has a much lower total energy compared with XA type. Half-metallicity and spin gapless semiconductor character have been predicted in XA type Zr 2 YAl, but these properties may be disturbed under the more stable L2 1 structure. The energy difference between the XA and L2 1 structures increases as Y atom varies from Cr to Ni. The reason has been discussed based on the charge density difference. The magnetic properties of Zr 2 YAl have been investigated, a new possible Slater-Pauling curve of M = Z−22 has been observed in Zr 2 CoAl and Zr 2 NiAl. [ABSTRACT FROM AUTHOR]

Competition between the highly-ordered XA structure and disordered L2 1 B structure in Heusler alloys Mn 2 CoZ (Z = Al, Ga, Si, Ge, Sb) has been investigated. The relative stability of the two structures strongly depends on the main group element Z. When Z belongs to Al or Ga, the XA structure is stabler, but when Z belongs to Si, Ge or Sb, the L2 1 B structure gains stability and is lower in energy. This is related to the different number of valence electrons in main group element Z, which influences the DOS structure near the Fermi level and changes N(E F ). The energy difference ΔE between the XA and L2 1 B structures may be used to estimate the tendency to form L2 1 B structure in different Heusler alloys qualitatively. A large negative ΔE is preferable to retard the A-C site disorder and retain the highly-ordered XA structure. That is just the case in Mn 2 CoAl. A robust half-metallicity is observed in Mn 2 CoSi, Mn 2 CoGe and Mn 2 CoSb, they are always half-metallic under either XA or L2 1 B structure. But in Mn 2 CoAl and Mn 2 CoGa, their spin gapless semiconducting character will be destroyed and replaced by a half-metallic state if L2 1 B disorder occurs. Finally, these results suggest that the L2 1 B structure should be considered together with XA structure when discussing the electronic structure of “inverse” Heusler alloys. [ABSTRACT FROM AUTHOR]

• Melt-spinning can help to reduce precipitation of the secondary phase and form a highly ordered structure in Heusler alloys Fe 2 CoSi 1-x B x (x = 0–0.25) • B atoms mainly enter the substitutional site in Fe 2 CoSi 1-x B x and single Heusler phase can be obtained when × = 0–0.10. • Fe 2 CoSi 1-x B x Heusler alloys are candidates for spintronic applications within the range of × = 0–0.1. • Deviation between the M s at 5 K and calculated total spin moment is observed when B content is high, resulting from the Fe 2 B-type secondary phase. A series of Fe 2 CoSi 1-x B x (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25) Heusler alloys has been synthesized using melt-spinning method, which can help to reduce the precipitation of the secondary phase and form a highly ordered structure. The XRD patterns indicate that, when x = 0–0.1 the Fe 2 CoSi 1-x B x melt-spun ribbons are single Heusler phases, but when x = 0.2 and 0.25 a small amount of secondary phase appears. The lattice constant decreases with increasing B content, suggesting that B mainly enters the substitutional sites of Si. The Curie temperatures T C of Fe 2 CoSi 1-x B x alloys are all higher than 1000 K, and a 21 K increase of T C is observed as x varies from 0 to 0.25. The hysteresis loops of Fe 2 CoSi 1-x B x alloys show soft magnetic character. Their saturation magnetizations M s at 5 K and 300 K are similar and close to 5μ B / f.u. The zero-gap half-metallic character reported for Fe 2 CoSi has been confirmed in present work. But with the substitution of B for Si, the Fermi level moves from the center in Fe 2 CoSi DOS to the left edge of the minority energy gap in Fe 2 CoSi 0.75 B 0.25 , which may disturb the half-metallic character when B content is high. When × = 0–0.1, the M s at 5 K of Fe 2 CoSi 1-x B x agree well with the calculated total spin moments, but when the B content is high, especially when x = 0.2 and 0.25, a deviation between the experimental and theoretical results is observed, which is related to the secondary phase in these samples. [ABSTRACT FROM AUTHOR]

• L2 1 B disordered structure has a higher stability in EQHA CoMnNiSn comparing with ordered Y-type structure. • L2 1 B disorder can suppress the martensitic transformation predicted in ordered CoMnNiSn. • CoMnNiSn bulk and ribbon samples are both ferromagnets with M s closing to 5.00 μ B /f.u. • Influence of atomic disorder is important when predicting the properties of Heusler alloys. Equiatomic quaternary Heusler alloy CoMnNiSn has been synthesized in both bulk and ribbon form to explain the contradictions in the magnetic properties and possible martensitic transformation between different literature. The structure, magnetic properties and electronic structure of CoMnNiSn were investigated both theoretically and experimentally. A cubic Heusler phase can be identified in the XRD patterns. A small amount of secondary phase is observed in bulk CoMnNiSn while it is eliminated in the melt-spun ribbons. The saturation magnetization M s at 5 K of bulk and ribbon CoMnNiSn are 4.85 μ B /f.u. and 4.76 μ B /f.u., respectively. This and also the calculation results suggest that ferromagnetic ground state has been established in CoMnNiSn samples. There is no trace of martensitic transformation in CoMnNiSn bulk and ribbon samples. The L2 1 B atomic disorder can be responsible for this, which comes from the random occupation of Co/Ni at A, C sites in the cubic lattice of CoMnNiSn and has a higher stability comparing with the ordered Y-type structure. This suppression effect is further explained by the weakening of the Jahn-Teller effect in the austenite DOS of L2 1 B type CoMnNiSn. All this calls for more attention to the effects of atomic disorder in the design of magnetic shape memory alloys in equiatomic quaternary Heusler alloys. [ABSTRACT FROM AUTHOR]

Heusler alloys Mn 2 RuGe and Mn 2 RuGa have been prepared by melt-spinning method successfully. Theoretical and experimental studies reveal a ferrimagnetic ground state in the two alloys. The Curie temperatures are 303 K for Mn 2 RuGe and 272 K for Mn 2 RuGa. The calculated total spin moments of Mn 2 RuGe and Mn 2 RuGa are integral values of 2.00 μ B and 1.03 μ B , respectively. And the theoretical spin polarization ratio is also quite high. However, due to the atomic disorder in the ribbons, the saturation moments of them measured at 5 K are smaller than the calculated values, especially that of Mn 2 RuGa. This coincides with the disappearance of the superlattice reflection (111) and (200) peaks in the XRD pattern of Mn 2 RuGa. Annealing Mn 2 RuGa ribbon at 773 K can enhance the atomic ordering. Both saturation magnetic moment and Curie temperature increase obviously after the heat treatment. [ABSTRACT FROM AUTHOR]

• Mn 2 Fe 1-x Co x Ga (x = 0–1) alloys have been synthesized and investigated. • Co-doping and melt-spinning can help to realize BCC Heusler phase in Mn 2 Fe 1-x Co x Ga. • Co-high Mn 2 Fe 1-x Co x Ga are promising candidates for spintronic applications. • FCC and BCC Mn 2 Fe 1-x Co x Ga have distinct magnetic properties. A series of Mn 2 Fe 1-x Co x Ga (x = 0–1) Heusler alloys was synthesized by melt-spinning method. The crystal structure, magnetic properties and electronic structure of them were investigated experimentally and theoretically. In undoped Mn 2 FeGa, a pure FCC phase is identified. The substitution of Co for Fe in Mn 2 Fe 1-x Co x Ga tends to stabilize the BCC Heusler phase, with the help of melt-spinning technique, single BCC Heusler phase was obtained within the range of × = 0.5–1.0. The FCC Mn 2 Fe 1-x Co x Ga are antiferromagnetic and their Néel temperatures T N decrease with Co-doping. But in BCC Mn 2 Fe 1-x Co x Ga, a ferromagnetic character is observed and the saturated magnetization M s at 5 K increases rapidly with increasing Co content. First-principles calculations suggest that Co-doping can make the formation energy of Mn 2 Fe 1-x Co x Ga BCC phase more negative and increase the phase stability, which agrees well with the appearance of the BCC phase in the XRD pattern when Co content is high. This effect can be explained from the change of electronic structure with Co-doping. The calculated total spin moments of Mn 2 Fe 1-x Co x Ga increase from 1.04μ B / f.u. for × = 0 to 2.01 μ B / f.u. for × = 1, following the Slater-Pauling curve of M = Z −24. The M s at 5 K agrees well with the theoretical results when × = 0.75–1.0. Calculations also suggest that Mn 2 Fe 1-x Co x Ga alloys all have 100% or quite high spin polarization ratio. All this makes them promising candidates for spintronic applications when Co content is high. [ABSTRACT FROM AUTHOR]

Highlights: [•] Based on DFT method, Ga2MnCo–Ga2MnV system is studied by isostructural alloying. [•] No martensitic transformation is found in both Ga2MnCo and Ga2MnV. [•] Potential ferromagnetic martensitic transformation is expected in Ga2MnV0.5Co0.5. [ABSTRACT FROM AUTHOR]

Highlights: [•] The static and dynamic magnetic properties of the Heusler alloy Cu2VAl are investigated. [•] The linear AC susceptibilities are analyzed by using the Vogel–Fulcher model and the critical slowing down power law. [•] It has been established that a spin glass behavior exists in this material at low temperature. [Copyright &y& Elsevier]

• Effect of Bi-doping on martensitic transformation in Heusler type MSMAs was investigated. • Bi-doping can suppress the martenstic transformation in Ni 2 MnGa 1-x Bi x and Mn 2 NiGa 1-x Bi x. • Electron density can be an appropriate factor to ascribe variation of martensitic transformation temperature. • Magnetic structures of Ni 2 MnGa and Mn 2 NiGa remain unchanged after Bi-doping. The effects of Bi-doping on the electronic structure, martensitic transformation and magnetic properties of Heusler alloys Ni 2 MnGa 1- x Bi x and Mn 2 NiGa 1- x Bi x (x = 0, 0.25, 0.5, 0.75, 1) were investigated theoretically. The substitution of Bi for Ga has a negative effect on the martensitic transformation. The total energy difference ΔE M between the martensite and austenite decreases gradually with the doping of Bi. When x = 0.5, 0.75 and 1.0 in Ni 2 MnGa 1- x Bi x and x = 1.0 in Mn 2 NiGa 1- x Bi x , the martensite phase becomes higher in energy comparing with the austenite. Thus the doping of Bi can lower the martensitic transformation temperature T M and finally suppresses it. The possible reasons for this trend are related to the increasing valence electron concentration e/a and cell volume V with Bi-doping. The competition between them may be ascribed further by the electron density, which combines the effect of valence electron concentration and size effect. The electron densities of Ni 2 MnGa 1- x Bi x and Mn 2 NiGa 1- x Bi x decrease monotonously with increasing Bi content. This agrees well with the variation of ΔE M or T M. The doping of Bi does not change the magnetic structure of Ni 2 MnGa 1- x Bi x and Mn 2 NiGa 1- x Bi x. The former is ferromagnetic and the latter is ferrimagnetic in both martensite and austenite state. These results can help to introduce new component like Bi to Heusler alloys and discover new functional materials in them. [ABSTRACT FROM AUTHOR]

Abstract: The thermodynamic, electronic and magnetic properties of Ni2MnX (X=Ge, Sn, Sb) Heusler alloys are investigated using the quasi-hormonic Debye model and the first principles calculation based on the density-functional-theory. The calculated results of the temperature dependent bulk modulus, coefficient of thermal expansion and the P–V relation for Ni2MnX (X=Ge, Sn, Sb) indicate that the bonding strength becomes stronger along the sequence of Ni2MnSb→Ni2MnSn→Ni2MnGe. The slower change trend of temperature dependent heat capacity of Ni2MnGe than that of Ni2MnSn and Ni2MnSb stems from the larger contribution of electronic heat capacity and smaller contribution of lattice heat capacity compared to the other two alloys. The ferromagnetic coupling order between the Ni and Mn is confirmed by our first principles calculations. The total moments in one primitive cell for the three alloys are all about 4.0μB which are mainly carried by Mn atom with about 3.5μB as can be seen from the magnetization density distribution. [Copyright &y& Elsevier]

Mn 2 NiGa 1-x Cr x (x = 0–0.5) alloys were synthesized successfully to explore possible Cr-based all- d -metal Heusler alloys with magnetic shape memory effects. When x = 0–0.25, Mn 2 NiGa 1-x Cr x are single BCC Heusler phase, but when x = 0.375 some FCC phase co-exists with the main Heusler phase, finally a pure FCC phase is formed in Mn 2 NiGa 0.5 Cr 0.5. In BCC Mn 2 NiGa 1-x Cr x , Cr-doping leads to the decrease of martensitic transformation temperature T M and increase of the saturation magnetization M s at 5 K. While the FCC phase does not show the trace of phase transition and has a very low magnetization till 5 K. First-principles calculations suggest that, in BCC Mn 2 NiGa 1-x Cr x the partial spin moment of Cr is large and parallel to that of Mn (B), which leads to the increase of M s when x = 0–0.25. A higher stability of the martensite than the austenite is found, which supports the phase transition observed experimentally. It may be noticed that the T M of Mn 2 NiGa 1-x Cr x decreases with both increasing e/a and decreasing cell volume, which is opposite to the empirical rule in traditional Heusler alloys. Calculation suggests that Cr–Ga disorder may be a possible reason for this decrease. • Heusler alloys Mn 2 NiGa 1-x Cr x were synthesized successfully. • Effect of Cr-doping on phase transition and magnetism of Mn 2 NiGa was studied. • Unlike traditional Heusler alloys, T M of Mn 2 NiGa 1-x Cr x decreases with increasing e/a and decreasing cell volume. • A new Mn 2 Ni(Ga, Cr) FCC phase was reported. [ABSTRACT FROM AUTHOR]

• New Fe 2 MnSi 1−x B x Heusler alloys have been synthesized. • B can enter substitutional or interstitial site, depending on its content. • B substitution can enhance ferromagnetism in Fe 2 MnSi obviously. • Mechanism for this enhancement was discussed in detail. A series of Fe 2 MnSi 1−x B x (x = 0–0.4) Heusler alloys was synthesized and investigated. The variation of lattice parameters with B content suggests that B prefers entering the substitutional site of Fe 2 MnSi when the amount is small. But when B content is high, it enters the interstitial site. A spin reorientation is observed at ~54 K in Fe 2 MnSi, which moves to low temperatures with increasing B content and disappears when x = 0.3. Both the Curie temperature T C and saturation magnetization M s increase with the substitution of B for Si. The M s gets closer to the calculated total spin moment M t. All this suggests that the dope of B can enhance the ferromagnetic character of Fe 2 MnSi 1−x B x. For the high B content, B-doping expands the lattice and enlarges the distance between magnetic atoms. This leads to the increase of Fe and Mn spin moments. The substitution of B for Si has an ordering-effect for Fe 2 MnSi lattice by forming a strong covalent bonding and relieves the possible Fe-Mn disorder. This effect also contributes to the increase of M s. [ABSTRACT FROM AUTHOR]