Magneto-Optic Properties of Ultrathin Nanocrystalline Ferrite Garnet Films in the 8K to 300K Temperature Interval

A study of the initial stages of crystallization in RF magnetron-sputtered ferrite garnet films is reported, in which a series of ultrathin Bi2Dy1Fe4Ga1O12 layers is fabricated and characterized. The spectral and temperature dependencies of magnetic circular dichroism (MCD) of these films are studied in the temperature range from 300 K down to 8 K. Measured magneto-optical properties are reported in the spectral range between 300 and 600 nm. In ultrathin garnets at temperatures below 160 K, we found that between 360 and 520 nm, the spectral MCD dependencies were typical of bismuth-substituted garnets with high levels of gallium dilution in the tetrahedral sublattice. The MCD signal strength measured at its 440 nm peak grows linearly with reducing temperature between 160 K and 8 K. This observed temperature dependency of MCD differed dramatically from these measured in thicker (3.7 nm) nanocrystalline garnet films. The peak MCD signal at 440 nm in these 3.7 nm-thick samples grows linearly from 215 K down to 100 K, resembling the same dependency seen in 1.7 nm films. In thinnest layers of thickness 0.6 nm, no MCD signals were observed at any temperature in the range between 8 and 300 K.