Magnetic and structural properties of Co(Fe)-Ni-Al(Ga) Heusler alloys*

Ferromagnetic shape memory alloys (FSMA) are promising candidates for application as actuators, sensors, magnetomechanical devices, harvesters, and magnetic cooling systems. In their low-temperature, low-symmetry phases they may also posses a considerable magnetocrystalline anisotropy, which is necessary for the FSMA but may render them useful as low-cost permanent magnets as well. Co(Fe)-Ni-Al(Ga) alloys are an interesting subgroup, as these materials are ductile, cheap, and easily synthesized, while possessing a high Curie and martensitic transformation temperature. In this work, we report on systematic first-principle investigations of the structural and magnetic properties of Co₂NiAl, Fe₂NiAl, and Fe₂NiGa-based Heusler alloys. We calculated the ground state energy and magnetic properties of different structural motives and degree of order. For the most favorable structures, we evaluated magnetocrystalline anisotropy, magnetic exchange coupling and lattice free energy to assess the equilibrium properties for the compositions under study.