Magneto-optical Faraday and Kerr effect of orthoferrite thin films at hightemperatures

Orthoferrites present, as bulk materials? reorientation transitions of thei r magnetic moment alignment at temperatures depending on the rare-earth (RE ) ion. In particular, orthoferrites (REFeO3) with RE = Sm, Dy, present this transition at T-SRT = 443 K and 36 K, respectively. The spectra of the com plex Kerr and Faraday angle have been measured on orthoferrite thin films ( RE = Sm, Dy, Y), which were prepared by pulsed laser deposition on amorphou s quartz substrates. The obtained spectra exhibit contributions of both sur faces and interfaces. Propagation effects of the polarized light in tile ma gnetooptical medium which is interpreted in terms of a simplified theoretic al formalism, is also observed. For selected photon energies, temperature d ependent Faraday rotation measurements, theta (F), on orthoferrite thin fil ms (RE = Sm, Dy, Y) have been performed. A quite different thermal variatio n compared to the bulk magnetization has: been observed. Curie temperatures are found to be close to the bulk values or slightly larger by 10 K to 20 K as in the case of DyFeO3 and YFeO3. For RE = Sm and Dy, theta (F) increas es with increasing temperature contrary to the saturation magnetization, pa sses through a maximum at about 460 K and vanishes with a T-C of 647 +/- 18 K, 695 K for RE = Sm and Dy respectively.