Anisotropy and Ferromagnetic Resonance in NiFe2O4 with [111] Texture

Abstract

Grain-oriented materials are useful in magnetic applications such as transformers and microwave devices. We have prepared [111]-oriented NiFe2O4, which shows a deviation of texture axes of less than 5°. Typical values for the ceramic quantities are: grain size is 60 microns, porosity is 3.5%, and resistivity is 104 ohm·cm. In a polycrystalline material with one fixed [111] axis and randomly distributed [100] axes, the anisotropy energy is minimum for K1<0 along the texture axis (θ=0°), maximum at θ=50°, and again a minimum at θ=90°. The latter energy minimum has the nature of a preferential plane. This is found in [111] texture for K1<0, and is not present in [100] or [110] textures. Measurements of the static torque and x-band ferromagnetic resonance show the expected behaviour. The variation of the resonance field with θ is in good agreement with theory, using the static K1 value. The variation of linewidth with θ illustrates the expected spread in resonance field. For θ=0° and θ=90°, the linewidth is minimum, rising by 700 Oe when θ is changed to 50° where the resonance lines become highly asymmetric.