Abstract
Magnetic resonance measurements have been made at 9.525 Gc/sec on two ferrite single crystals Ni0.782+Fe0.162+Fe2.023+O4 and Mg0.88Fe0.212+Fe1.973+O4 in the temperature range 4° to 20°K. Both samples exhibit induced anisotropy when cooled from above 12°K in a magnetic field. The associated shifts in the field for resonance indicate an induced uniaxial anisotropy energy in both samples of the form K′ Σiαi2βi2, where αi and βi are the direction cosines of the magnetization at the measuring temperature and the annealing temperature, respectively. The shifts in resonance fields due to the anneal decrease smoothly as the measuring temperature is raised and disappear above 12°K. The similarity of the induced anisotropy for both samples irrespective of the difference in compositions suggests that the source is the same and is associated with the Fe2+ ion. The observed symmetry could arise from the proposed directional ordering of the interstitial cations. Since, however, the magnesium ferrous ferrite has, within the limits of chemical analysis, a cation excess while the nickel ferrous ferrite has a cation deficiency, this seems unlikely. Our results thus support the contention that preferentially oriented distortions associated with the Fe2+ ion are responsible for the low-temperature induced anisotropy in nickel ferrous ferrite and also, as reported here, in magnesium ferrous ferrite.
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