E. A. Petrzhik

Magnetoplastic Effect: Basic Properties and Physical Mechanisms

This paper presents a review of the main results of investigations into the magnetoplastic effect, which manifests itself in motion of dislocations in crystals exposed to magnetic fields. The dependences of the mean free path of dislocations on the induction and direction of the magnetic field, the magnetic treatment time, the temperature, and the type and concentration of impurities are studied for NaCl, LiF, CsI, Zn, Al, and InSb crystals. The threshold magnetic field Bc below which the effect is absent, the saturation field B0 above which the mean free paths of dislocations remain constant with an increase in the magnetic induction B, and the critical frequency vc of rotation of a sample in the magnetic field above which the effect disappears are examined. The quantities Bc, B0, and vc are investigated as functions of the basic physical parameters. It is found that the magnetoplastic effect is highly sensitive to X-ray radiation at low doses and to simultaneous action of an electric field or mechanical loading. The hardening of NaCl(Pb) crystals in the magnetic field is revealed. The theoretical interpretation is proposed for all the findings and dependences observed.

Change in the microhardness of nonmagnetic crystals after their exposure to the Earth’s magnetic field and AC pump field in the EPR scheme

Changes in the microhardness of ZnO, triglycine sulfate (TGS), and potassium acid phthalate (KAP) crystals after their exposure to crossed ultralow magnetic fields, i.e., the Earth’s field BEarth ≈ 50 μT and the alternating-current field

Determination of the positions of impurity centers in a dislocation core in a NaCl crystal from magnetoplasticity spectra

\tilde B \approx 3 \mu {\rm T}

Change in dielectric properties of triglycine sulfate in a constant magnetic field

orthogonal to it, have been revealed. In ZnO crystals, the microhardness increases, whereas in TGS and KAP, it decreases. A maximum change (10–15%) is reached within 1–3 h after magnetic treatment; then, the microhardness gradually recovers to its initial value for the first day. After a sufficient pause, the effect is completely reproduced under the same conditions. The resonant frequency of the pump field

Resonance magnetoplasticity in ultralow magnetic fields

\tilde B

Low-frequency spectra of dislocation paths in NaCl crystals in the electron spin resonance scheme

corresponds to the EPR condition with a g-factor close to two. The magnetic memory exhibits a strong anisotropy: for each of the crystals, a direction is found, which, being coincident with the Earth’s magnetic field vector BEarth, causes complete or partial suppression of the effect. In ZnO and TGS crystals, these are symmetry axes 6 and 2, respectively. In the KAP crystal, it is the direction in the cleavage plane orthogonal the 2 axis. Possible physical mechanisms of the observed phenomena have been discussed.