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• 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]

• 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]

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]