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

摘要

Orthoferrites present, as bulk materials, reorientation transitions of their magnetic moment alignment at temperatures depending on the rare-earth (RE) ion. In particular, orthoferrites (REFeO_3) with RE = Sm, Dy, present this transition at T_(SRT) = 443 K and 36 K, respectively. The spectra of the complex Kerr and Faraday angle have been measured on orthoferrite thin films (RE = Sm, Dy, Y), which were prepared by pulsed laser deposition on amorphous quartz substrates. The obtained spectra exhibit contributions of both surfaces and interfaces. Propagation effects of the polarized light in the magneto-optical medium which is interpreted in terms of a simplified theoretical formalism, is also observed. For selected photon energies, temperature dependent Faraday rotation measurements, Θ_F, on orthoferrite thin films (RE = Sm, Dy, Y) have been performed. A quite different thermal variation 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 DyFeO_3 and YFeO_3. For RE = Sm and Dy, Θ_F increases with increasing temperature contrary to the saturation magnetization, passes 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.