The Faraday rotation of bismuth- and thulium-substituted yttrium iron garnet

Abstract

The substitution of bismuth in the dodecahedral site of rare-earth garnet films is known to enhance the Faraday rotation by orders of magnitude. The effect of the bismuth ion on the iron sublattice that produces this enhancement is not known, and experimental evidence suggests that the rare-earth ion is not a significant contributor to the Faraday rotation. As the Faraday rotation probes the orbital angular momentum states of the garnet film, Tm3+-substituted yttrium iron garnet (YIG) films were investigated because of the large orbital contribution to the angular momentum and the crystal-field effect of the Tm ion. The temperature dependence of the Faraday rotation in Tm:YIG did not show any significant variations other than the bismuth enhancement. The major contribution to the Faraday rotation comes from the tetrahedral symmetry site, which is evaluated from the fit of the experimental data to a simple sublattice model. The temperature dependence of the Faraday rotation is presented between 4 and 300 K at wavelengths of 546, 578, and 633 nm. The liquid-phase epitaxial films have a composition of Y2.4−xTmxBi0.6Fe5−yGayO12, where x=1.2, y=0; x=1.9, y=1.3; and x=2.4, y=1.3. The Faraday rotation passes through a compensation point in the Ga-doped samples, and the Faraday rotation is shown to be independent of the Tm concentration.