The Effect of a Temperature Gradient in a Single Crystal on E.P.R. Line Shape and Width

Abstract

Temperature is an important parameter in electron paramagnetic resonance experiments and studies at different temperatures can give a great deal of useful information about the investigated spin system and its interaction with its environment. Generally speaking, all of the parameters in the spin-Hamiltonian, such as the g factor, hyperfine interaction constants, etc., are independent of the temperature to a first-order approximation, but the line shape, line width, and spin-lattice relaxation time are quite sensitive to temperature changes. However, e.p.r. studies in many natural or synthetic crystals with very low concentrations of paramagnetic impurity-ions indicate that the line width ?H and the line shape are virtually independent of the temperature T (provided T is not too low), while the crystal-field parameters in the spin-Hamiltonian, such as D and E, show a considerable variation with temperature. The former comes about because the line widths in such cases depend mainly on the mosaic structure (Shaltiel and Low 1961; Wenzel and Kim 1965) and the local distortions (mechanical or electrical strains) (Wenzel and Kim 1965) of the crystal lattice which are practically independent of the temperature. The latter is mainly due to the shrinkage or expansion of the crystal which changes the interactions between the paramagnetic ion and its neighbouring ions.