Preparation of thin ferrite films on silicon substrates

Thin-films of (Ni,Zn)Fe₂O₄ were grown by means of RF sputtering on Si (100) and (111) substrates. Films with a thickness up to 100 nm were prepared for analysis purposes, enabling the optimization of the sputter process. The purpose of these ferrite thin films is the preparation of MFM cantilever-coatings for use with a high-frequency magnetic force microscope (HF-MFM). As a basis for these probes, we employ commercial, micromachined silicon cantilevers which exhibit (100)-oriented Si surfaces on the shank, and (111)-oriented surfaces on the pyramid-like tip end. The substrates were not additionally heated during the evaporation. A slow cooling enabled the grain growth, so that grains of about 30 - 50 nm diameter were produced. Hysteresis loops of the (Ni,Zn)Fe₂O₄ films were obtained using a VSM magnetometer at room temperature. The films were found to exhibit the behaviour of a soft magnetic material, which is well suited for the HF-MFM imaging of harddisk recording heads up to a carrier frequency of 2 GHz. The material properties of the (Ni,Zn)Fe₂O₄ thin films are characterized by means of transmission electron microscopy (TEM). An electron backscatter diffraction (EBSD) analysis of the individual grain orientations is carried out on this type of ferrite films. This enables a determination of the magnetization direction of individual grains, which contributes to the modelling of the tip properties. The current goal for further research is the preparation of even thinner ferrite coatings in order to maintain a small tip radius at the tip end of the cantilever, which is an important factor for the achievable spatial resolution of a MFM image.