High-Temperature Electronic Relaxation at the Rare-Earth Ions in Garnets

Abstract

The electronic relaxation times at Tb3+, Sm3+, and Tm3+ ions in magnetic iron and nonmagnetic gallium and aluminum garnets have been studied by gamma-gamma angular correlation experiments. The relaxation time of Tb3+ in iron garnets reaches a minimum value of ∼10−11 sec at higher temperatures, considerably larger than similar values for the Sm3+ and Tb3+ ions in iron garnets. The Tb3+ ion relaxation time in iron garnet was independent of temperature from below room temperature to 1100°K. This result suggests that the transitions which determine the relaxation time occur between closely spaced levels. In Sm3+ in iron garnets the relaxation time τs∼[exp(Δ/KT)−1] with Δ/K=250°K, while in Tm3+ τs∼T−1. No significant differences were observed between the relaxation times in magnetic iron and nonmagnetic gallium or aluminum garnets at room temperature. In the case of Sm3+ and Tm3+ where no temperature saturation effects have been observed this result seems to indicate that processes involving spin magnon interactions and phonon modulation of the exchange field do not play a dominant role in the rare-earth ion relaxation process in rare-earth iron garnets at room temperature.