Electric amplification of the magnetoplastic effect in nonmagnetic crystals

Abstract

An experimental study of the electric field influence on the magnetoplasticity is performed for NaCl and LiF crystals. It is shown that even rather weak electric fields of E∼1–10 kV/m strongly amplify the magnetoplastic effects of both “signs.” In crystals, such as NaCl(Ca), where the magnetic transformation of impurities in dislocation cores decreases the dislocation pinning, the mean dislocation path l in the magnetic field B abruptly increases under an electric field applied along with B. Also in crystals such as NaCl(Pb), where, conversely, a magnetically induced growth of the pinning force occurs, the electric field again amplifies the magnetic effect, this time suppressing a dislocation mobility. In both cases, no electric effects at B=0 are observed. Measurements at the temperatures of 77, 165, and 293 K displayed a thermally activated character of the electric actions. An activation analysis was performed for the two types of NaCl crystals, manifesting a magnetic softening. The found activation energies, U(E), revealed a monotonous decrease in E and coinciding magnitudes U(0)≈0.2 eV. It was also shown that an electric field does not destroy the dependencies of the mean dislocation path l on the induction B and the impurity concentration C:l∝1/C[1+(B0/B)2]. The observed electric effects can be associated with electromigration of charged cation vacancies in the vicinity of dislocation cores. This apparently increases the number of magnetically active pinning ions Me+ of the bivalent impurity Me (say, Ca, Mg, etc.) replacing the ordinary diamagnetic ions Me2+. Analogous effects are also expected in ferroelectrics and semiconductors.