Magneto-optical effect induced by spin chirality of the itinerant ferromagnet Nd2Mo2O7

It is demonstrated both theoretically and experimentally that the spin chirality associated with a noncoplanar spin configuration produces a magneto-optical effect. Numerical study of the two-band Hubbard model on a triangle cluster shows that the optical Hall conductivity ${\ensuremath{\sigma}}_{xy}(\ensuremath{\omega})$ is proportional to the spin chirality. The detailed comparative experiments on pyrochlore-type molybdates ${R}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$ with $R=\mathrm{Nd}$ (Ising-like moments) and $R=\mathrm{Gd}$ (Heisenberg-like ones) clearly distinguishes the two mechanisms, i.e., spin chirality and spin-orbit interactions. It is concluded that for $R=\mathrm{Nd},\phantom{\rule{0.2em}{0ex}}{\ensuremath{\sigma}}_{xy}(\ensuremath{\omega})$ is dominated by the spin chirality for the dc $(\ensuremath{\omega}=0)$ and the $d\ensuremath{\rightarrow}d$ incoherent intraband optical transitions between Mo atoms.