Temperature-dependent magnetic properties of YIG thin films with grain size less 12 nm prepared by a sol-gel method

We report on YIG film with small grain size (<12 nm) that has the potential to be used in microwave device application. The nanostructured film has been deposited on quartz substrate by a sol-gel spin coating technique, followed by annealing at temperatures in the range between 700 and 900 °C. The structural and magnetic properties of the film in the range 10-610 K were investigated. The X-ray diffraction results demonstrate that the films formed in a polycrystalline structure with lattice parameter in the range of 12.249-12.359 Å, lower than that of bulk materials. The saturation magnetization decreased not linearly with increasing the temperature from 10 to 300 K, differently from that reported for the bulk YIG. The coercivity value decreased with increasing temperatures (10-300 K), except for the film annealed at 800 °C. The Curie temperature of the film annealed at 700 °C was 554 K, however, other films showed higher Curie temperature values than that reported for bulk YIG. These properties are strongly influenced by the stress in the film's structure due to the different thermal expansion coefficient of the YIG and the quartz substrate.