Competing magnetic phase in the tetragonal NiPtMnGa alloy: Role of disorder

The effect of Pt substitution on the structural and magnetic properties of NiPtMnGa alloys was investigated using ab-initio calculations. For ordered systems, FM structure was found to be the most stable among competing magnetic ones. However, the calculated magnetic moment of 4.13μB was significantly overestimated compared with the experimental value of 2.2 μB. This spin rearrangement was unable to reproduce the experimental magnetic moment. To solve this problem, the effect of disorder was also studied. Five magnetic configurations, namely Ferromagnetic (FM), Anti-ferromagnetic (AFM-1), Anti-ferromagnetic (AFM-2), Ferrimagnetic (FiM), and Antisite ferrimagnetic (AS) phases, were investigated and compared. FM phase remained the most stable with an overestimated magnetic moment of the order of 4.174 μB. However, FiM and AS phases were found to accurately reproduce the experimental magnetic moment value. Calculations show that FiM is better suited for the NiPtMnGa alloy comparing to the AS phase, exhibiting a more stable equilibrium energy and a magnetic moment of 2.068 μB.