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

摘要

This paper describes some new systems F1-xAx, 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, Tc=455°C. A is antiferromagnetic potassium ferrite (KFe11O17, TN=530°C) which crystallizes in the closely related β-alumina structure. Mixtures F1-xAx 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 σs, intrinsic coercive force Hci, torque L, and rotational hysteresis Wr, from -197° to 480°C. The observation of nonvanishing rotational hysteresis, sinθ torque curves, displaced hysteresis loops and changes in σs 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 A0′≈√ 3A0 and C0′≈C0.