Intrinsic hard magnetism and thermal stability of a ThMn12-type permanent magnet

Abstract

Herein, we theoretically demonstrate that simple metal (Ga and Al) substitutional atoms, rather than the conventional transition metal substitutional elements, not only stabilize the ThMn12-type SmFe12 and Sm(Fe,Co)12 phases thermodynamically but also further improve their intrinsic magnetic properties such that they are superior to those of the widely investigated SmFe11Ti and Sm(Fe,Co)11Ti magnets, and even to the state-of-the-art permanent magnet Nd2Fe14B. More specifically, the quaternary Sm(Fe,Co,Al)12 phase has the highest uniaxial magnetocrystalline anisotropy (MCA) of about 8 MJ m−3, anisotropy field of 18.2 T, and hardness parameter of 2.8 at room temperature and a Curie temperature of 764 K. Simultaneously, the Al and Ga substitutional atoms improve the single-domain size of the Sm(Fe,Co)12 grains by nearly a factor of two. Numerical results of MCA and MCA-driven hard magnetic properties can be described by the strong spin-orbit coupling and orbital angular momentum of the Sm 4f-electron orbitals.