Effective Hamiltonian and ground state properties of rare-earth ions in iron garnets

Abstract

An effective Hamiltonian for ground Kramers doublet and quasidoublet of non-Kramers rare-earth (RE) ions in garnets in the presence of exchange interactions with ferric sublattices is shown to reflect the anisotropy of both crystalline field and exchange interaction with different consequences for Kramers and non-Kramers ions. For ten ions of the RE series all possible crystal-field ground states which are to be considered in RE garnets are examined. Main attention is paid to the search for RE moments with Ising-like character imprinted by the crystal field. The exchange interaction of such moments with iron sublattices can then be described by a single-parameter Hamiltonian. This greatly simplifies general many-parameter theories of the low-temperature magnetic phenomena. It is found that in principle the Ising-like ground states may occur in Sm 3+-, Tb 3+-, Dy 3+- and Tm 3+-iron garnets. The results are compared with available experimental data.