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 σ_xy(ω) is proportional to the spin chirality. The detailed comparative experiments on pyrochlore-type molybdates R₂Mo₂O₇ with R=Nd (Ising-like moments) and R=Gd (Heisenberg-like ones) clearly distinguishes the two mechanisms, i.e., spin chirality and spin-orbit interactions. It is concluded that for R=Nd, σ_xy(ω) is dominated by the spin chirality for the dc (ω=0) and the d→d incoherent intraband optical transitions between Mo atoms.