Effect of Co on Magnetic Properties of ErFeO3, HoFeO3, and DyFeO3

Magnetization data have been obtained on crystals of RFe_1-xCo_xO₃, with 0<x≤0.06 and R=Er, Ho, and Dy, at temperatures between 4.2° and 300°K. The spontaneous magnetization σ₀ lies along the a axis of the orthorhombic unit cell for x≥0.01. For R=Er and Ho, the data are compared with σ₀ ∥ a at low temperatures for the pure compounds (x=0). A Weiss molecular field of (10.5±1.0) kOe is found for the Ho³⁺ ions. The Dy compounds undergo a transition to a state with σ₀=0 at low temperatures. The transition temperature increases from 35°K at x=0 to a maximum of 133°K at x=0.003. A formalism is developed for describing the concentration dependence of the spin-reorientation temperatures, and the behavior in DyFe_1-xCo_xO₃ is related to changes in the anisotropy fields on the Fe³⁺ sublattices.