Effects of rare earth oxide addition on NdFeB magnets.

Abstract

Effects of rare-earth oxides addition on the magnetic properties of the Nd-Fe-B sintered magnets are studied. The addition of Dy₂O₃ and Tb₄O₇ increases the intrinsic coercivity. For Dy₂O₃ addition, the optimum conditions for the powder mixing and Dy₂O₃ particle size are determined. A mixing time of over 10 minutes and the Dy₂O₃ particle size under 3μm are required to obtain a high intrinsic coercivity. EPMA measurements on NdFeBAl magnets added with Dy₂O₃ reveal an inhomogeneous distribution of Dy in the Nd₂Fe₁₄B matrix; Dy is rich near the grain boundary but poor inside of the matrix. Formation of such an inhomogeneous distribution of Dy atoms is attributed to reduction of Dy₂O₃ in the Nd-rich phases followed by diffusion of the Dy atoms into the matrix.