Acoustic detection of resonance plasticization of LiF crystals under the effect of crossed magnetic fields in the EPR scheme

The authors of current work were the first to predict theoretically and to show experimentally that the joint action of crossed permanent B₀ and high-frequency (HF) B^∼ magnetic fields could lead to resonance plasticization of nonmagnetic crystals when frequency ν of the HF field satisfies the condition of electron paramagnetic resonance (EPR) h ν = g μ_B B_o, where h is the Plan's constant; g is the Lande factor; μ is the Bohr magneton. In this work the experimental results on the effect of crossed magnetic fields in the EPR scheme on the dislocation internal friction of LiF crystals are discussed. The preliminary experiments, carried out by the method of microindentation, showed that, in the LiF crystals under study in crossed magnetic fields in the EPR scheme, the resonance displacement (depinning) of dislocations occurred. The effect was maximum at the frequency of 9.525 MHz which satisfies the condition of paramagnetic resonance at g =2 (B_o = 340 μT, B^∼ =10 μT); the frequency of the HF field varied in the interval from 9.2 to 9.8 MHz. These data were used when performing the acoustic measurements. From the results of preliminary experiments, it is obvious that the observed increase in mechanical energy dissipation was caused by breakaway of dislocations from pinning centers, induced by the magnetic field. The physical cause of the effect is the structural deformation of impurity centers in the dislocation-impurity nanoreactor in the result of paramagnetic resonance. Thus, the possibility of acoustic detection of resonance plasticization of nonmagnetic crystals under the effect of crossed fields in the EPR scheme is shown for the first time. (author)