Laboratory of Mechanical Properties of Crystals

The magnetoplastic effect (MPE) is a change in the mechanical properties of non–magnetic crystals under the influence of a magnetic field. It was discovered in our laboratory as the movement of individual dislocations in NaCl crystals placed in a constant magnetic field in the absence of other external influences. Along with the usual MPE, which corresponds to the plasticization of the crystal, a negative MPE was also found: the hardening of crystals in a magnetic field. Both in situ effects, which manifest themselves only during exposure, and magnetic memory effects are observed, in which the "magnetized" crystal retains its changed properties for some time. The physical nature of MPE consists in a magnetically induced change in the state and structure of paramagnetic impurity complexes. The transformation of the center occurs after the evolution of its spin subsystem into a state in which the quantum ban on a certain electronic transition is lifted, radically changing its structure. This can be accompanied by both a decrease and an increase in the height of the impurity potential barrier for dislocation movement. The effect is manifested both in microplasticity: dislocations move in a magnetic field by tens and hundreds of microns, and in macroplasticity: the yield strength of a crystal in a magnetic field can change several times, as well as in microhardness (changes after magnetic treatment can be ~ 10-20%) and in changes in other mechanical properties of crystals. Magnetic influences can be created in a constant field mode (a crystal between the poles of a magnet), an alternating field (rotation of the sample in a magnetic field or in a resonant mode when the crystal is placed in crossed magnetic fields: constant and variable at a frequency corresponding to the EPR condition. Some time ago, we discovered a resonant MPE in the Earth's magnetic field (~50 µT), when the variable pumping field (~2-3 µT) changes at radio frequencies (~1 MHz).