The physical kinetics of magnetoplasticity of diamagnetic crystals
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SORDER, AND PHASE TRANSITION IN CONDENSED SYSTEMS
The Physical Kinetics of Magnetoplasticity of Diamagnetic Crystals A. L. Buchachenko Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, 119991 Russia e-mail: [email protected] Received September 5, 2006
Abstract—The kinetic equations describing the rate of magnetically induced release of dislocations entrapped by stoppers were solved. The magnetic field effect on the mobility of dislocations was calculated. Its comparison with experiment gave the ratio between the rate constants for two key processes governing magnetoplasticity, namely, singlet–triplet conversion in a spin nanoreactor and the release of a dislocation from it. The kinetic criterion of the existence of magnetoplasticity as a physical phenomenon was obtained. PACS numbers: 61.72.Hh DOI: 10.1134/S1063776107100068
1. INTRODUCTION The magnetoplasticity of diamagnetic crystals, that is, the magnetic field dependence of their strength, plasticity, and other deformation properties, cannot be explained in terms of the energy dogma, because the energies of a crystal and its atom-molecular constituents acquired in a magnetic field are negligibly small. According to the authors who discovered magnetoplasticity [1–7], the motion of dislocations, which determines the mechanics and plasticity, is related to the generation of paramagnetic electron-spin states in the crystal whose spin governs the stopper + trapped dislocation system. This idea was developed in [8, 9], where an atom-molecular model of a spin nanoreactor created in the stopper + dislocation system was suggested. This model was used to explain the origin of magnetoplasticity in a constant magnetic field and in microwave fields, both resonance and nonresonance, in ionic and covalent crystals [9]. The purpose of this work was to present the physical kinetics of processes in spin nanoreactors, derive and solve the kinetic equations for magnetically induced detachment (release) of dislocations from stoppers, quantitatively determine the ratios between the rate constants for the key elementary processes that control magnetoplasticity, and compare the results with experimental data.
localized on the dislocation, and the other, on the stopper. This pair can exist in two spin states, singlet and triplet. The back transfer of the electron with the return to the dislocation fixed on the stopper occurs in the singlet state only. In the triplet state, it is spin-forbidden. Next, a magnetic field induces singlet-triplet spin conversion and changes its rate and the populations of the singlet and triplet states. Lastly, Coulomb attraction is “switched off” (completely or partially) in both singlet and triplet spin states. Coulomb attraction holds the dislocation in the trapped state in the initial system, and spin transfer and the creation of a spin pair therefore virtually releases the dislocation. These are the three key conditions of magnetoplasticity. The phenomenon itself can only exist when all of them are satisfied jointly. Let us
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