Multiple slow relaxation of magnetization in Dy3+ confined in the crystal matrix of rare-earth-calcium silicates with the apatite structure

Abstract

Apatite-type silicates Y_7.75Dy_0.25Ca₂(SiO₄)₆O₂ and Dy₈Ca₂(SiO₄)₆O₂ were prepared by high-temperature solid state synthesis. In the crystal lattice, Dy³⁺ partially substitutes Ca²⁺, preferably at the 6h Ca2-site, and forms a short bond of 2.2 Å with the intra-channel O²⁻. The imposed strong ligand field anisotropy provides large magnetic anisotropy, which manifests itself as slow relaxation of magnetization at low temperatures. The magnetic dynamics is characterized by three or two characteristic values of relaxation time, respectively, which may be attributed to a single Dy³⁺ center. A phenomenological model is proposed which explains this response in terms of single paramagnetic center multiple relaxation.