First-principles investigation of the magnetic structures and pressure-induced magnetic phase transition in magnetocaloric MnRhAs

Magnetic interactions in magnetocaloric compound, MnRhAs, was investigated using density functional theory calculations. The cooperation between direct and indirect spin exchange couplings results in various interesting magnetic phases depending upon temperature and pressure. Direct Rh-Rh and Rh-Mn spin exchange couplings are weak due to small moments on the Rh atoms and indirect Mn-Mn spin exchange couplings are dominant in MnRhAs. Intra-layer Mn–Mn couplings could be rationalized by a superexchange mechanism, whereas inter-layer Mn–Mn couplings can be explained by RKKY interactions. The nature, i.e., ferromagnetic or antiferromagnetic, of RKKY interactions is very sensitive to the change of metal-metal distance, so the magnetic ordering in MnRhAs is rather susceptible to changes of volume, which could be achieved by changing pressure, temperature, or chemical doping. This distinctive property of MnRhAs makes it a superb candidate for magnetocaloric and other magnetic applications.