Temperature dependences of the parameters of the initial splitting of Gd3+ in CaMoO4 (lattice and spin–phonon contributions)

Abstract

The electron paramagnetic resonance (EPR) spectra of Gd³⁺ impurity centers in CaMoO₄ single crystals have been investigated at temperatures T = 1.8, 4.2, and 99–300 K. The temperature dependences of the spin Hamiltonian parameters b_n^m(T) (n = 2, 4, m = 0, 4) have been determined, and their analysis has been carried out. The temperature contributions from the static lattice, b₂(L) and b_4m(L), to the spin Hamiltonian parameters b_n^m(T) have been separated. For this purpose, the changes of the static lattice contributions b₂(L) and b_4m(L) have been determined taking into account the temperature shifts of the oxygen ions nearest to the Gd³⁺ ions in CaMoO₄ single crystals. The differences b_nm(F) = b_n^m–b_nm(L) have been attributed to the spin–phonon contribution. The analysis of the results obtained has demonstrated that the parameters b₂₀(F) and b_4m(F) are positive, and the dependence of b₂₀(F) on the temperature T is well described in the model of local vibrations (G. Pfister). However, the temperature behavior of the parameter b_4m(F) could not be described in the framework of the well-known models of the spin–phonon interaction.