Effects of magnetic fields on the dislocation unlocking from paramagnetic centers in non-magnetic crystals

Abstract

Displacements of dislocations as a result of exposing the specimens to a static magnetic field ( B=0.1−2 T) in the absence of mechanical loading in the temperature interval T=4.2−293 K were found and investigated for NaCl, CsI, LiF, Zn and Al single crystals. This effect is characterized by the following properties: the mean dislocation path l increases linearly with the time t of the magnetic treatment; the mean dislocation velocity ν is proportional to the square of the magnetic magnetic induction ( ν∝ B 2) and inversely proportional to the square root of the concentration of paramagnetic impurities ( ν∝1 √C ); the effect is temperature independent in the range T = 4.2–77 K and it grows only by 20%–30% with a further increase in T up to room temperature; l( t) and l( B) saturate at large values of t and B at a level corresponding to an average distance between “forest” dislocations; an abrupt decrease in the effect is found when the frequency ν of an alternating magnetic field exceeds some critical value ν c ∝ B 2 ( ν c ≈ 15 Hz at B = 0.3 T). The phenomenon is interpreted as a result of unlocking of dislocations from paramagnetic centers under the action of an external magnetic field and motion of dislocations in the long-range internal stress field.