Memory Effects in Magnetoplasticity of NaCl Crystals

Memory effects in magnetoplasticity of NaCl crystals with different impurity content have been studied. Dislocation paths and microhardness of crystals after their exposure to a constant magnetic field or to crossed ultralow magnetic fields are measured. In two crystals, noticeable relaxation displacements of dislocations, introduced after exposure, are found. In two other crystals with a lower impurity concentration, the paths remain at the background level, but in one of them the exposure causes an increase in the density of mobile dislocations. Similar magnetic exposure also leads to a decrease in the microhardness of crystals, but to different extent. Interpretation of observations is reduced to a spin-dependent transformation of impurity centers in a magnetic field, which plastisizes the crystal. Introduction of dislocations after magnetic exposure leads to their relaxation displacements from unstable positions, and at strongly weakened pinning centers dislocation immediately occupy positions close to equilibrium.