Temperature and hydrostatic pressure dependences of the b40spin-Hamiltonian parameter for Gd3+in fluoroperovskite single crystals

Abstract
Both the temperature and the pressure dependences of the b40 spin-Hamiltonian parameter for RbCaF3, CsCaF3, RbCdF3 and TlCdF3 doped with Gd3+ have been reported. On the assumption that b40 depends on the metal-ligand distance according to a law b40 approximately rk the following values of k were obtained: -20.9, -27.1, -24.9 and -29.3, respectively. It was found that the temperature dependence of b40 is predominantly caused by spin-phonon interactions which were estimated to contribute about 68% to the total dependence observed. The effectiveness of some theoretical models predicting the role of vibronic contributions is also discussed.