Effect of increasing pH value on the structural, optical and magnetic properties of yttrium iron garnet films prepared by a sol-gel method

摘要

Yttrium iron garnets (Y3Fe5O_(12), YIG) nano-particles thin films with different pH values (pH 1, 2, 3, 4 and 5) were prepared by a sol-gel method. The films were deposited on quartz substrates using a spin coating technique. Annealing of the films was performed at 900 °C in air for 2 h. The structural analysis using an X-ray diffrac-tometer (XRD) exhibited that all films were single phases regardless the differences in pH value. The lattice parameters calculated from the XRD patterns revealed that the distortion of lattice occurred at a high pH value. The crystallites sizes of films also increased from 27.6 to 33.3 nm when the pH value increases from 1 to 5. The films were high agglomeration due to increasing of pH value which caused difficulty to measure the grain size. The films with different pH values showed transmission >80 % in visible range. Additionally, the absorption coefficient (a) of films was found to be of the order of 10~7 cm~(-1). A strong absorption of the films caused by charge transfer transition centered in UV and optical transitions between crystal field levels within the 3d levels of Fe~(3+) ions. The YIG films exhibit highest saturation magnetization value of 76 emu/cm3 at pH 1. The increment of pH value up to 5 caused a decreasing of coercive field due to multidomain formation and the easy movement of the domain walls.