Large coercivity and enhanced magnetization in La-substituted Sm6Mn23 alloys

Abstract

The magnetic properties of Sm₆Mn₂₃-based alloys are still not fully understood for their high complexity in magnetic and crystallographic structures. This work presents studies of the structure and magnetic properties of Sm₆Mn₂₃ and Sm₅LaMn₂₃ alloys. The results show that both the binary and La-substituted ternary alloys crystallize in a cubic Th₆Mn₂₃ type structure (Fm-3m) with trace amount of Mn impurities. The lattice parameter of Sm₅LaMn₂₃ is slightly larger than that of Sm₆Mn₂₃. The Curie temperature of Sm₅LaMn₂₃ is ∼403 K, which is lower than that of Sm₆Mn₂₃. A field-dependent magnetic transition was observed in Sm₅LaMn₂₃, which shows a decreasing temperature at which Sm₅LaMn₂₃ exhibiting maximal magnetization with increasing field, indicating a suppression of the antiferromagnetic coupling of the rare earth and Mn moments under applied field. Large coercivities up to 0.74 T and 1.2 T are observed in Sm₅LaMn₂₃ bulk alloys and powders, respectively. The saturate magnetization, the remanent magnetization, and the coercivity of Sm₅LaMn₂₃ at 5 K are much higher than that of Sm₆Mn₂₃. The ball-milled Sm₅LaMn₂₃ powders exhibit significantly enhanced coercivity and magnetization. The refinement of the grain size during ball-milling results in the enhanced coercivity. The magnetic purification of the powders and possible local ferromagnetic configuration of the surface Mn atoms may result in the enhanced magnetization.