Magnetic phase diagram and anisotropy of pseudoternary (${\mathrm{Er}}_{\mathrm{x}}$${\mathrm{Dy}}_{1\mathrm{-}\mathrm{x}}$${)}_2$${\mathrm{Fe}}_{14}$B compounds

A complete study of the magnetic phase diagram and magnetic anisotropy of pseudoternary (${\mathrm{Er}}_{\mathrm{x}}$ ${\mathrm{Dy}}_{1\mathrm{-}\mathrm{x}}$ ${)}_2$ ${\mathrm{Fe}}_{14}$B compounds has been carried out by the use of low-field ac magnetic susceptibility, magnetization, and singular-point detection measurements on magnetically aligned samples. A cone magnetic structure has been observed in compounds with 0.6≤x<0.9, even at low temperatures, and the thermal dependence of the cone angle for each concentration has been determined. Substitution of Er by Dy gives rise to a significant modification of the magnitude and temperature dependence of the anisotropy field $H_A^{\mathcal{’}}$ (i.e., the field on the basal plane), a linear dependence being observed with Dy concentration at 293 K. The present data have been interpreted in terms of a crystalline-electric-field–mean-field model. The inclusion of only second- and fourth-order crystal-field terms is enough to account for the phase diagram and the cone magnetic structure. The fourth-order terms should necessarily be included into the Hamiltonian in order to account for the variation of angle of the cone magnetic structure, both with temperature and concentration.