Laser-induced THz piezomagnetism and lattice dynamics of antiferromagnets MnF2 and CoF2

The piezomagnetic effect manifests itself in emergence of a net magnetic moment in a mechanically-stressed magnetically ordered material. Up to now, this effect was theoretically analyzed and experimentally studied for the case of static or low frequency deformations of antiferromagnets, and in our brief overview we present the recent progress in exploring the piezomagnetic effect at the THz frequencies. We discuss particular lattice distortions in the model piezomagnetic antiferromagnets MnF2 and CoF2 that are associated with the Raman-active phonons. We show that the phonons of the Eg and B2g symmetry should support emergence of a dynamic magnetic moment oscillating at the corresponding THz phonon frequencies. We further analyze conditions for coherent excitations of these modes by using ultrashort laser pulses via the mechanism of impulsive stimulated Raman scattering. We show that observation of transverse piezomagnetic effect is, in principle, feasible for the Eg phonon. We also discuss experimental results demonstrating laser-induced excitation of coherent Eg phonon in MnF2 and CoF2, as well as speculate about possibilities to detect piezomagnetic effect at the THz frequencies.