Magnetic anisotropy of R2[Co1−xFex]17

Abstract

The magnetic anisotropy (temperature‐composition) phase diagram of the rare‐earth compounds R₂[Co_1−xFe_x]₁₇ can be rationalized by taking account of the magnetic anisotropy of the background Co‐Fe, the shape of the rare‐earth 4f charge cloud, the dependence of T_C on x, and therefore, the strong composition dependence, at fixed temperature, of the rare‐earth magnetic anisotropy. This suggests two phase diagrams, one for oblate and one for prolate ions. For the first set (Pr, Nd, Tb, Dy, Ho), the easy direction should be in the plane except within a U‐shaped region above a spin reorientation boundary extending roughly from x = 0.05 to x = 0.5. For the prolate ions (Sm, Er, Tm, Yb), there should be two isolated easy plane regions: one at temperatures above T_sr and for 0⩽xsr and for 0.5<x⩽1, or so. The rest of the (T, x) plane should be easy axis.