Technique for Determining Spin-Lattice Relaxation Times

Abstract

Experiments were performed so that the static dc susceptibility of a paramagnetic material could be measured as a function of microwave power absorbed at electron spin resonance. The spin-lattice relaxation τ1 can be expressed by τ1=[(χ0−χp)/PaΓm]MsBdc2 where Pa is the microwave power necessary to change the field independent static susceptibility from χ0 to χp. χp is the steady state static susceptibility of the sample when it is absorbing Pa amount of microwave power. Bdc is the homogeneous dc field produced by the laboratory magnet, Ms is the weight of the sample, and Γm is a constant whose value depends solely upon the system of units used. The relaxation time is determined by directly measuring Pa, Ms, B, χ0, and χp/χ0. The apparatus, the experimental techniques, and the accuracy of the measurements are described in some detail.