MAGNETOPLASTIC EFFECT AND SPIN-LATTICE RELAXATION IN A DISLOCATION-PARAMAGNETIC-CENTER SYSTEM

A magnetic induction threshold B-c above which the magnetoplastic effe ct - depinning of dislocations from paramagnetic pinning centers - can be observed in samples placed in a magnetic field is predicted and ob served in Al, NaCl, and LiF crystals. The existence of a threshold is associated with the fact that for B<B-c the spin-lattice relaxation ti me tau(sl) in a dislocation-paramagnetic-center system is less than th e time required for spin evolution in a magnetic field resulting in th e removal of the spin forbiddenness of an electronic transition that ' 'switches off'' the dislocation-pinning-center interaction. It is show n that the threshold field B-c is sensitive to temperature and x-ray i rradiation of the samples. A new method for measuring the spin-lattice relaxation time in paramagnetic centers on dislocations is proposed o n the basis of the data obtained. (C) 1995 American Institute of Physi cs.