Crystal-field interactions and spin reorientation in (Er1-xDyx)2Fe14B.

Abstract

Spin reorientation in (${\mathrm{Er}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Dy}}_{\mathrm{x}}$${)}_{2}$${\mathrm{Fe}}_{14}$B alloys has been investigated by means of $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy on magnetically aligned samples. For 0<x<0.5, the magnetization direction is found to change continuously from the basal plane to the tetragonal c axis with increasing temperature. Reorientation temperatures decrease with increasing Dy concentration, as expected from competition between the uniaxial anisotropy of Dy and the basal anisotropy of Er in the ${R}_{2}$${\mathrm{Fe}}_{14}$B (R a rare-earth atom) structure. Data are quantitatively interpreted with a model incorporating crystal-field and exchange interactions as well as Fe-sublattice and R dipolar anisotropies. The stability range of the basal-plane magnetization extends up to ${x}_{c}$\ensuremath{\simeq}0.5 at low temperatures, while the model predicts ${x}_{c}$=0.26 if only ${B}_{2}^{0}$${O}_{2}^{0}$ and ${B}_{2}^{2}$${O}_{2}^{2}$ terms are considered; inclusions of ${B}_{4}^{0}$${O}_{4}^{0}$ and ${B}_{6}^{0}$${O}_{6}^{0}$ terms provide a satisfactory fit to our ${T}_{r}$ versus x data.