EXPERIMENTAL STUDY OF SPIN-LATTICE RELAXATION BY THE ORBACH PROCESS IN NEODYMIUM MAGNESIUM NITRATE.

Abstract : Measurement was made of the spin-lattice relaxation time of trivalent Nd ions in Nd-Mg nitrate by fitting Casimir-du Pre dispersion curves to the frequency dependence of the self-inductance of a coil into which the sample could be inserted. The difference in self-inductance, with and without the sample, was determined by a modified Owen bridge at liquid helium temperatures and in fields between zero and 1800 oe. In the 3.3-4.2K range the Orbach process dominates and is identified by its characteristic exponential inverse temperature variation. For H perpendicular to the crystal axis, good agreement was found with Orbach's theory for the magnetic field dependence of this process. As by-products of the experiments, determination was also made of the magnetic specific heat constant and the temperature-independent susceptibility. (Author)