Magnetic Phase Transitions in Ultrathin YFeO3 Films According to Synchrotron Mössbauer Reflectometry Data

The magnetic properties of ultrathin single-crystal Y57FeO3 orthoferrite films have been studied by Mossbauer reflectometry. Mossbauer spectra were measured using the ESRF synchrotron in the reflection geometry. As the temperature changes from 3.6 to about 773 K, the splitting of the Zeeman sextet in the spectra successively decreases and, simultaneously, a quadrupole doublet appears in them, which indicates the development of a magnetic phase transition. From the temperature dependences of the magnetic hyperfine field B-hf for the main orthorhombic Y57FeO3 phase, N & eacute;el temperatures equal to T-N approximate to 593, 562, and 567 K and the critical parameter values equal to beta approximate to (0.28-0.3) +/- 0.02 are determined in films with thicknesses of 28, 6.5, and 4 nm, respectively. An analysis of changing ratio of the line intensities in the Zeeman sextet with temperature makes it possible to trace the successive rotation of the direction of the antiferromagnetic axes in Y57FeO3 toward the surface plane with an increase in the temperature and a decrease in the film thickness.