Mechanical properties, strength physics and plasticity

Resonant dislocation motions in NaCl crystals under EPR conditions in the Earth’s magnetic field with a radio-frequency pump field

V. I. Alshits^a, E. V. Darinskaya^a, V. A. Morozov^b, V. M. Kats^b, A. A. Lukin<sup>b

a</sup> Institute of Cristallography Russian Academy of Sciences, Moscow
^b Saint Petersburg State University

Abstract: Three resonant peaks $l(\nu)$ of dislocation paths, appearing in NaCl crystals under simultaneous exposure to the Earth’s magnetic field $\mathbf{B}_{\mathrm{Earth}}$ and an ac pump field $\mathbf{\tilde{B}}$ have been observed in the radio-frequency range ($\nu\sim$ 1 MHz). Each peak corresponds to a specific experimental geometry. Resonance frequencies correspond to ordinary EPR conditions in which, however, instead of the total Earth’s field, its projections onto particular crystallographic directions play part. These directions are probably related to orientations of magnetic moments at impurity centers in dislocation cores. A physical model describing well the positions all three EPR peaks $l(\nu)$ is proposed. The peak height $l_m$ is proportional to the squared amplitude of the pump field and the time $t$ of sample exposure to crossed fields: $l_m\propto\tilde B^2_mt$. The threshold amplitude $\tilde{B}^{\mathrm{th}}_m\sim$ 1 $\mu$T of the pump field is detected, below which the effect rapidly disappears. The time of spin-lattice relaxation of radical pairs on dislocations is estimated by the threshold field $\tilde{B}^{\mathrm{th}}_m$ level.

Received: 30.03.2011

 English version: Physics of the Solid State, 2011, 53:10, 2117–2125

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