Nanocrystallization in FINEMET-Type Fe_73.5Nb₃Cu₁Si_13.5B₉ and Fe_72.5Nb_1.5Mo₂Cu_1.1Si_14.2B_8.7 Thin Films

A growing variety of microelectronic devices and magnetic field sensors as well as a trend of miniaturization demands the development of low-dimensional magnetic materials and nanostructures. Among them, soft magnetic thin films of Finemet alloys are appropriate materials for sensor and actuator devices. Therefore, one of the important directions of the research is the optimization of thin film magnetic properties. In this study, the structural transformations of the Fe_73.5Nb₃Cu₁Si_13.5B₉ and Fe_72.5Nb_1.5Mo₂Cu_1.1Si_14.2B_8.7 films of 100, 150 and 200 nm thicknesses were comparatively analyzed together with their magnetic properties and magnetic anisotropy. The thin films were prepared using the ion-plasma sputtering technique. The crystallization process was studied by certified X-ray diffraction (XRD) methods. The kinetics of crystallization was observed due to the temperature X-ray diffraction (TDX) analysis. Magnetic properties of the films were studied by the magneto-optical Kerr microscopy. Based on the TDX data the delay of the onset crystallization of the films with its thickness decreasing was shown. Furthermore, the onset crystallization of the 150 and 200 nm films began at the temperature of about 400-420 °C showing rapid grain growth up to the size of 16-20 nm. The best magnetic properties of the films were formed after crystallization after the heat treatment at 350-400 °C when the stress relaxation took place.