Preparation and magneto-optical properties of BiY2Fe5O12 organic nanocomposite films

Bi-substituted yttrium iron garnet with a composition of BiY2Fe5O12 (Bi-YIG) nanoparticles was prepared via mechanochemical processing and subsequent heat treatment. The maximum milling time was 8 h and the annealing was carried out at different temperatures up to 1000 °C for 4 h. Phase formation of the as-milled and annealed powders was investigated by X-ray diffraction (XRD). This investigation shows that there was no trace of garnet phase in the as-milled powder or the powders annealed below 800 °C. In the XRD patterns of the powders annealed above 800 °C, the peaks belonging to the garnet phase appeared and a single-phase garnet was finally obtained at 950 °C. Magnetic parameters of the powders were measured, using a SQUID unit, and a saturation magnetization of 22 Am2/kg was obtained. Mean crystallite size of the single-phase powder, which was evaluated by Scherrer's formula was about 45 nm. Morphology of the powders was investigated by TEM, which shows that the particles were agglomerated. The single-phase powders were then dispersed in an organic binder for various Bi-YIG/binder weight ratios and for various dispersing times up to 80 h to obtain magnetic inks. Particulate films were made by the spin-coating method, using the magnetic inks. Magneto-optical properties (Faraday rotation) of the spin-coated films were investigated in the visible wavelength range of 470–625 nm. The results show that as Bi-YIG/binder weight ratios increases, the values of the Faraday rotation spectra increase too and their maximum values shift to shorter wavelengths.