Abstract
Extensive X-band EPR measurements have been carried out on -doped single crystals of (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0), covering the temperature range 4.2–290 K. The spin-Hamiltonian parameters (SHP) are evaluated by the use of a rigorous least-squares fitting procedure. The systematics of the SHP are studied both as functions of x and of temperature. Newman’s superposition model has been applied to the calculation of SHP; it is found that the calculated values agree quite well with the experimental values, provided that one considers minor distortions of the positions of the eight fluorine ions surrounding the ion. The temperature variation of SHP has been explained to be predominantly due to spin-phonon interaction and partially due to thermal expansion of the crystal lattice. Finally, the average - exchange interaction, averaged over the nearest and next-nearest neighbors, has been estimated, in , to be 3.8±2.5 GHz, as found by the application of the molecular-field model using the g shift from the isostructural diamagnetic host, , at liquid-helium temperature.
- Received 28 March 1988
DOI:https://doi.org/10.1103/PhysRevB.38.8673
©1988 American Physical Society