Spin-lattice relaxation of Fe3+ in iron doped magnesium oxide

Abstract

Spin-lattice relaxation measurements for Fe3+/MgO were carried out in the temperature range from 4.2 to 27 K at 37.5 Hz utilizing the pulse saturation method. This revealed a close agreement with the theoretical predictions, demonstrating aT −1 behaviour at low temperatures as a direct process and aT −4.6 variation as a raman process at higher temperatures, with a transition temperature near 20 K between these two regimes. Measurements oft 1 were carried out for samples with iron concentrations of 140, 310 and 110 ppm and gave the values of 1.0, 0.8 and 0.1 msec, respectively, at 4.2 K. This confirms that the inverse proportionality oft 1 with concentration holds over this range of samples. Variation of relaxation timet 1 with crystal orientation for the central transition of Fe3+/MgO revealed two minima that were explained as due to crossrelaxation mechanisms. Comparison of our results with both those computed by Shiren at 10 GHz and the experimental results of Castle and Feldman at the same frequency showed that at 1 ∝ (frequency)−4 law was obeyed. The present data has provided another example of anS-state ion behaving in the manner predicted by the present theories of relaxation.