Peculiar temperature dependence of magneto-optic Kerr rotation associated with antiferromagnetic-paramagnetic transition

We investigate the magneto-optic Kerr effect in perpendicularly magnetized Pt/Co/Ir/Cr2O3/Pt thin films, associated with the antiferromagnetic-paramagnetic transition of the Cr2O3 layer. The magneto-optic Kerr rotation angle (theta (K)) shows oscillatory behavior as a function of the photon energy of incident light owing to interference in the Cr2O3 layer. The temperature dependence of theta (K) at 2.67 eV (lambda = 465 nm), at which the largest theta (K) is obtained, shows a sharp dip at 287.0 K. The dip temperature is similar to the reported Neel temperature for Cr2O3 thin films. Although the theta (K) spectra measured at several temperatures are generally explained by the classical interference model, theta (K) is enhanced at 2.36-2.79 eV (lambda = 525-445 nm) close to the dip temperature. This peculiar enhancement in theta (K) is discussed on the basis of the anomaly in the optical parameters of the Cr2O3 layer associated with the antiferromagnetic-paramagnetic transition.