Determination of the magnetic and nuclear structure of Ni _{2.17} Mn _{0.83} Ga

Abstract

The structure of Ni2.17Mn0.83Ga has been investigated as a function of temperature using neutron powder diffraction. Above T = 310 K the compound has the cubic L21 structure, with lattice parameter a = 5.79 A, and with the excess nickel atoms occupying the vacant manganese sites. Magnetisation and resistivity measurements indicate a Curie temperature of T = 340 K with a further transition at T = 301 K associated with a structural phase transition. The martensitic phase was found to have a tetragonal structure with cell parameters a = b = 3.87 A and c = 6.47 A and space group I4/mmm. Although there is negligible change in atomic volume the lattice parameters a and b change by ∼5.5% and the c-axis by almost 12%. The large change in cell parameters and the relatively high transition temperature make the compound a promising candidate for applications.