Dislocation paths in a magnetic field

Influence of a magnetic field on dislocation paths in crystals with paramag netic obstacles is studied. The model incorporates, as the most important a spect, a dependence of the energy of dislocation-obstacle bonds on their sp in multiplicity. An increase of the crystal plasticity in a magnetic field is explained by an increased population of high spin states with lower bind ing energy. The dependence of the average dislocation path length on the ma gnetic field accounting also for the hyperfine interaction between electron and nucleus spins is obtained. The theory agrees well with the available e xperimental data in a wide range of magnetic fields. The hyperfine interact ion is shown to play a crucial role, especially at relatively low magnetic fields. The possible dependence of plastic properties of crystals on the va lue of nuclear spin may lead to a magnetic isotope effect in plasticity. Th e hyperfine interaction may effectively suppress the contribution of parama gnetic obstacles in the magnetoplastic effect if the external magnetic fiel d is smaller than a certain value that is specific for each particular type of the obstacle.