EPR of Gd$\text{}^{3+}$-Doped La$\text{}_{0.9}$Nd$\text{}_{0.1}$F$\text{}_{3}$ Crystal: Spin-Phonon Interactions and Spin-Lattice Relaxations

The X-band EPR study of Gd$\text{}^{3+}$-doped La$\text{}_{0.9}$Nd$\text{}_{0.1}$F$\text{}_{3}$ single crystal in the temperature range 4.2-295 K is carried out in order to investigate crystal field effects, the Gd$\text{}^{3+}$ spin-phonon interactions, as well as Gd$\text{}^{3+}$ and Nd$\text{}^{3+}$ spin-lattice relaxation times. The local distortions at 4.2 K of the positions of the eight F$\text{}^{-}$ ions surrounding the Gd$\text{}^{3+}$ ion in the La$\text{}_{0.9}$Nd$\text{}_{0.1}$F$\text{}_{3}$ crystal were determined from comparison of the theoretical with the experimental spin-Hamiltonian parameters. The spin-phonon interactions can be described by the Einstein model, which better characterizes the behavior of paramagnetic centers in LaF$\text{}_{3}$ and La$\text{}_{0.9}$Nd$\text{}_{0.1}$F$\text{}_{3}$ crystals than the Debye model. It is suggested, from the rotational invariance mechanism for phonon-induced contributions to spin-Hamiltonian parameters, that the rotational contributions are much smaller than those from the strain.