Effect of B doping on phase transition and magnetic properties of Mn50Ni40In10-xBx: Experimental and theoretical investigation

A series of Mn50Ni40In10-xBx (x = 0 - 4) alloys was synthesized and the effect of B-doping on the structure, phase transition and magnetic properties in them has been investigated theoretically and experimentally. It is found that increasing boron content leads to the contraction of cell volume and increase of the martensitic transformation temperature. The doping of B also enhances antiparallel coupling between Mn spin moments in martensitic Mn50Ni40In10-xBx and lowers the Curie temperature of the austenite. Electronic structure calculations were carried out based on Mn50Ni37.5In12.5 and Mn50Ni37.5In6.25B6.25 supercells, which were close to the experimental compositions. The extra Ni atoms substituting for In/B prefer entering Mn (A) site and push Mn to the D site. In austenite ferromagnetic coupling between Mn moments on B, D sites is preferable, while in martensite the coupling between them becomes antiferromagnetic, which leads to a decrease of the total spin moment compared with the austenite. The total energy difference between the cubic austenite and tetragonal martensite increases with the substitution of boron, implying the increase of phase transition temperature. This can be explained from their DOS structures. These results agree well with experimental results and make reasonable explanation for them.