Intrinsic hard magnetism and thermal stability of a ThMn12-type permanent magnet
T. Ochirkhuyag, Soon Cheol Hong, Dorj Odkhuu
Abstract
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 ThMn 12 -type SmFe 12 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 SmFe 11 Ti and Sm(Fe,Co) 11 Ti magnets, and even to the state-of-the-art permanent magnet Nd 2 Fe 14 B. 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 4 f -electron orbitals.