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 ferri tes with composition NixFe3- O-x(4) With x = 0.9, 1.0, 1.2. Measuremen ts have been carried out by means of an automatic technique based on a modified short-circuited SMA transmission line. Linewidths ranged fro m 40 Oe to 80 Oe in all the temperature range. The dependence of the F MR linewidth with temperature leads to a contribution of the valence-e xchange mechanism for x < 1 and a contribution of the Ni2+ ion acting as a slowly relaxing impurity for x > 1. The collection of data obtain ed by the automatic system allows us to achieve the values for the rel axation times and activation energies of these mechanisms.