SEDL / STP / STP1304-EB / STP11745S

Magnetoplastic Effect: Relaxation of the Dislocation Structure and Microcreep of Nonmagnetic Crystals

Alshits, VI
Institute of Crystallography, Moscow,

Darinskaya, EV
Institute of Crystallography, Moscow,

Kazakova, OL
Institute of Crystallography, Moscow,

Mikhina, EY
Institute of Crystallography, Moscow,

Petrzhik, EA
Institute of Crystallography, Moscow,

Pages: 9    Published: Jan 1997

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Abstract

A new physical phenomenon—the dislocation displacements as a result of exposing specimens to a static magnetic field (B = 0.1-27) in the absence of mechanical loading—is discovered and investigated for sodium chloride, cesium iodide, lithium fluoride, zinc, and aluminum (NaCl, Csl, LiF, Zn, and AI) single crystals. This effect is characterized by the following properties: The mean dislocation displacement or path ℓ is proportional to B², inversely proportional to the square root of the concentration C of paramagnetic impurities, and increases linearly with time t of the magnetic treatment; there is no influence of the magnetic field on dislocation mobility in crystals with diamagnetic impurities; the effect is temperature independent in the range T = 4.2-77 K and grows only by 20% with a further increase of T up to room temperature; the saturation of ℓ(t) and ℓ(B) dependencies takes place at large values of t and B on the level corresponding to an average distance between the “forest” dislocations; an abrupt decrease of the effect is found when the frequency v of an alternating (over orientation) magnetic field exceeds some critical value vc ∝ B2, independent of T and C, but sensitive to a type of impurity, to X-ray irradiation, and different for edge and screw dislocations; a strong effect of a static electric field (E = 0.2-12 kV/m) on the mobility of charged dislocations in NaCl and LiF specimens simultaneously exposed to a static magnetic field is found (with no electric influence at B = 0); and the critical level Ec is found above which there is no saturation of dislocation displacements ℓ (B, t)—that is, the transition from a relaxation of dislocation structure to a microcreep is observed at E > Ec.

phenomenon is interpreted as a result of unlocking of dislocations from paramagnetic centers because of spin-dependent electron transitions in a dislocation-impurity system under the action of external magnetic field with further motion of dislocations in the long-range internal stress field combined with an electric driving force when an electric field is applied.