Resonant dislocation motion in NaCl crystals in the EPR scheme in the Earth’s magnetic field with pulsed pumping

Resonant dislocation motions in NaCl(Ca) crystals under the simultaneous action of the Earth’s magnetic field $\mathbf{B}_{\mathrm{Earth}}$ ($\sim$66 $\mu$T) and a pulsed pump field $\tilde{\mathbf{B}}$ of sufficient amplitude $\tilde{B}_m$ and certain duration $\tau$ have been detected and studied. The measured dislocation path peaks $l(\tau)$ have a maximum at $\tau = \tau_r\approx$ 0.53 $\mu$s. The resonance criterion has been found to be the ordinary EPR condition in which the $g$-factor is close to 2 and the optimum inverse pulse duration $\tau_r^{-1}$ is used instead of the harmonic pump field frequency $\nu_r$. The largest peak $l(\tau)$ height is reached at mutually orthogonal dislocation $(\mathbf{L})$ and magnetic field ($\mathbf{B}_{\mathrm{Earth}}$ and $\tilde{\mathbf{B}}$) orientations. Pulsed field rotation to the position $\tilde{\mathbf{B}}\parallel \mathbf{B}_{\mathrm{Earth}}$ significantly decreases but does not “kill” the effect. For dislocations parallel to the Earth’s field $(\mathbf{L}\parallel\mathbf{B}_{\mathrm{Earth}})$, the resonance almost disappears even at $\tilde{\mathbf{B}}\perp\mathbf{B}_{\mathrm{Earth}}$. In the optimum geometry of experiments, as the pump field amplitude $\tilde{B}_m$ decreases from 17.6 to 10 $\mu$T, the path peak height $l_r = l(\tau_r)$ decreases only by 7.5%, remaining at the level of $l_r\sim$ 10$^2$ $\mu$m, and at a further fall-off to 4 $\mu$T, it rapidly decreases to background values. In this case, the relative density of mobile dislocations similarly decreases from $\sim$90 to 40%. Possible physical mechanisms of the observed effect have been discussed.