Magnetic Exchange Anisotropy in Mixtures of Barium, Strontium, or Lead Ferrite with Potassium Ferrite

This paper describes some new systems F_1−xA_x, showing exchange anisotropy at room temperature and above. F is ferrimagnetic lead (P), barium (M), or strontium (S) ferrite, all with the magnetoplumbite structure, PbFe₁₂O₁₉, T_c=455°C. A is antiferromagnetic potassium ferrite (KFe₁₁O₁₇, T_N=530°C) which crystallizes in the closely related β‐alumina structure. Mixtures F_1−xA_x were prepared with 0≤x≤1. Specimens were cooled from above 600°C to room temperature in a field of 4 kOe and measurements made of the magnetic saturation σ_s, intrinsic coercive force H_ci, torque L, and rotational hysteresis W_r, from −197° to 480°C. The observation of nonvanishing rotational hysteresis, sinθ torque curves, displaced hysteresis loops and changes in σ_s are interpreted in terms of exchange anisotropy in the M A and P A systems; compositions in the S A system behaved as simple mixtures of magnetic and nonmagnetic phases. X‐ray diffraction indicated the formation of a new phase A′, possibly related to the development of exchange anisotropy. The identity of A′ has not been established; it may be a potassium‐rich superstructure of A with lattice parameters $A_0\mathrm{\prime \approx }\sqrt{3}{A}_0$ and C₀′≈C₀.