Effect of slowly relaxing impurities on ferrimagnetic resonance linewidths of single crystal nickel ferrites

Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 77 K to 400 K in single crystal nickel ferrites with composition Ni/sub x/Fe/sub 3-x/O/sub 4/ with x=0.9, 1.0, 1.2. Measurements have been carried out by means of an automatic technique based on a modified short-circuit SMA transmission line. Linewidths ranged from 40 Oe to 80 Oe in all the temperature range. The dependence of the FMR linewidth with temperature leads to a contribution of the valence-exchange mechanism for x<1 and a contribution of the Ni/sup 2+/ ion acting as a slowly relaxing impurity for x>1. The collection of data obtained by the automatic system allows the authors to achieve the values for the relaxation times and activation energies of these mechanisms.<
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