The infra-red Faraday effect andgvalues in rare-earth garnets

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Abstract
Measurement of the Faraday effect in single crystals of rare-earth garnet ferrites at wavelengths around 5 μm allows the determination of the g values of ions in the system. Experimental results are given in the temperature range 77 °K to 300 °K for the materials R3Fe5O12, where R = Y, Gd, Y0 5Gd0 5, Tm or Dy. The g values of gadolinium and ferric ions are observed to be constant over the whole temperature range and are in reasonably good agreement with previous measurements by alternative methods. In thulium ions the g value is observed to be 1.36 ± 0 03 at 77 °K and 1 64 ± 0 06 at 300 °K with a roughly linear variation at intermediate temperatures. In dysprosium ions the respective values are 0.77 ± 0 02 and 1 06 ± 0 04. These values are in poor agreement with measurements at microwave resonance. There is evidence that Kittel fast-relaxation effects explain the differnce. Such effects are not present at optical frequencies.