Static and Dynamic Contributions to the Splitting of the Eu²⁺ Ground State in SrMoO₄

Abstract

The EPR spectrum of an Eu²⁺ impurity center in a SrMoO₄ single crystal in the temperature range T = 1.8, 111–300 K has been studied, and the temperature changes in the spin Hamiltonian parameters describing the EPR spectrum of odd europium isotopes have been determined. It is shown that small temperature changes in the diagonal parameters of the spin Hamiltonian (for odd Eu²⁺ isotopes) $b_{2}^{0}$(T) = b₂(F) + b₂(L) and $P_{2}^{0}$(T) = P₂(F) + P₂(L) are explained by the compensation of spin–phonon contributions b₂(F) and P₂(F) by the contributions of the lattice thermal expansion b₂(L) and P₂(L). The quantities b₂(L) and P₂(L) that are dependent on the static lattice parameters at a given temperature, are estimated in terms of the superposition Newman model. Then, the spin–phonon b₂(F) and P₂(F) contributions determined by the lattice ion vibrations are separated. An analysis shows that $b_{2}^{0}$(F) and $P_{2}^{0}$(F) > 0, b₂(L) and P₂(L) < 0, and the temperature behavior of the spin–phonon contribution is well described by G. Pfister’s model of local vibrations.