Phonon Spectroscopy of the Schottky-Like Low-Energy Paramagnetic Excitations in Garnet Solid Solution Crystals

Abstract

The interaction of weakly nonequilibrium phonons with the low-energy paramagnetic excitations of the rare-earth ions of the yttrium series in rare-earth garnet solid solutions is studied at liquid-helium temperatures. The interaction of nonequilibrium phonons with the low-energy excitations of Ho3+ and Tb3+, which are caused by local electric fields in a crystal lattice, is experimentally investigated. In the row of Kraemrs ions (where the nature of low-energy excitations is caused by the splitting of the ground level of a paramagnetic ion due to the local magnetic fields of neighboring ions), interaction in the nonequilibrium phonon–low-energy excitation system is only detected in the Er-containing solid solutions and is absent in the structures containing Gd3+, Dy3+, and Yb3+ rare-earth ions. In the two-level system model, the efficiency of interaction and the transport characteristics of thermal phonons are shown to depend on the type of rare-earth ion, the energy and spectral features of two-level systems, the moments of electrons in the 4f shell, and spin–lattice relaxation.