Magneto-optical properties of La_0.7Sr_0.3MnO ₃ thin films with perpendicular magnetic anisotropy

We report the magneto-optical (MO) properties of compressively strained La0.7 Sr0.3 Mn O3 (LSMO) thin films epitaxially grown on a LaAl O3 substrate. The magnetic force microscope images show the stripe magnetic domains, characteristic of films with the perpendicular magnetic anisotropy (PMA). The optical reflectance and transmittance of the samples were measured over a broad energy range from the far infrared through the ultraviolet. To extract the optical constants of the films, we analyzed all of the layers of this thin-film structure using a Drude-Lorentz model. From the parameters obtained, we compute the optical constants, such as frequency-dependent optical conductivity and the diagonal components of the dielectric tensor. Moreover, the MO polar Kerr spectra of the samples were measured in an applied magnetic field of 1.5 T between 0.74 and 5.8 eV. The off-diagonal components of the dielectric tensor were then calculated by analyzing Kerr rotation, ellipticity, and the determined diagonal elements of the dielectric tensor. These functions yield information about the spin-dependent electronic structures of the LSMO thin films. We observed several MO-active transitions above 2 eV. These bands arise from the Mn-d (t2g) to Mn-d (eg) in the majority-spin channel and the onset of O-2p to Mn-d (eg) and O-2p to Mn-d (t2g) transitions in the minority-spin channel, in accord with the band-structure calculations. Most interestingly, their peak position and intensity are dependent on the film thickness, suggesting possible applications for tailoring MO responses in these PMA thin films.