Selection Rules for Light-Induced Magnetization of a Crystal with Threefold Symmetry: The Case of Antiferromagnetic NiO

We propose Raman-induced collinear difference-frequency generation (DFG) as a method to manipulate dynamical magnetization. When a fundamental beam propagates along a threefold rotational axis, this coherent second-order optical process is permitted by angular momentum conservation through the rotational analogue of the umklapp process. As a demonstration, we experimentally obtained polarization properties of collinear magnetic DFG along a [111] axis of a single crystal of antiferromagnetic NiO with micromultidomain structure, which excellently agreed with the theoretical prediction.

Figure 1

(a) Changes of $J_z^{\mathrm{EM}}$ by creation or annihilation of photons propagating along the $z$ axis. The lower panels show schematics of the changes of the angular momentum in collinear scattering processes of photons to a mode with (b) the same helicity and (c) the opposite, and (d) a collinear DFG process allowed along a threefold axis involving two photons with opposite helicity.

Figure 2

(a) Schematics of spin alignment in three $S$ domains belonging to the $T_1$ domain, and (b) random distribution of four orientations of $T$ domains within the coherent length ${\lambda }_C$ of the light beam. (c) Experimental and (d) calculated magnetic susceptibility of NiO; $\Gamma =70\mathrm{GHz}$ and ${\epsilon }_r=12.25$ are assumed.

Figure 3

(a) Schematics of the experimental setup. The inset shows the relation between crystal and laboratory coordinates. (b) Temporal waveform of the radiation from NiO and (c) its Fourier transformed spectrum. Polar plots of the transverse components (d) $M_x^{(2)}$ and (e) $M_y^{(2)}$ of the induced magnetization as functions of the crystal rotation angle $\theta$. The dots are experimental data of their amplitude, and the solid curves are calculated by Eq. (11).