The Preparation And The Performance Study Of The FeCo-ZnO Nano-granular Thin Film

With the rapid improvement of modern science and technology, miniaturization and high performance of electro-magnetic devices, high frequency soft magnetic thin films with high saturation magnetization Ms, low coercive force Hc, high electrical resistivity p and appropriate anisotropy field Hk, have attracted more and more attention for years. Nano-granular films, composing of magnetic metal and non-magnetic insulator matrix, is one of the most interesting films because this kind of films possess the advantages of magnetic metal (high Ms Tc) and insulator (high p) at the same time. This kind of nano-granular thin films have been one of hot points in the investigation of soft magnetic material. Up to now, there is no work studying the granular films composited of magnetic metal and semiconductor matrix systematically, so the purpose of this work is preparing (Fe65Co35)x-(ZnO)1-x nano-granular films with high performance by RF magnetron sputtering and studying the characters of the films.In this paper, a series of (Fe65Co35)x-(ZnO)1-x soft magnetic nano-granular films were prepared on glass substrates by magnetron sputtering (JGP560CⅣmodel). The structure and microstructure were analysed by x-ray diffraction (XRD) and high resolution transmission electronic microscopy (HRTEM). We use vibrating sample magnetometer (VSM) and dc four-probe method to determine the magnetic properties and the electrical properties respectively while the permeability spectra were characterized by the vector network analyzer using the shorted microstrip transmission-line method. We proved the feasibility of preparing the nano-granular films composited of magnetic metal and semiconductor matrix. The main conclusions are briefly introduced as follows:1. It can be seen that the sample consists of bcc Fe65Co35 particles and fcc ZnO from the HRTEM image and the XRD spectrum. The size of FeCo particles reduces with decreasing x, which indicates the existing of refinement effect of ZnO on FeCo grain.2. The dependence of Hce and Hk on metal volume fraction x was systematically studied. With decreasing x, Hce decreases first, and then increases with decreasing x. When x= 0.67, the value of Hce is obviously smaller than that of other samples. Hk increases first, then decreases. Furthermore, Hk is larger than 40 Oe with x from 0.82 to 0.63. The excellent soft magnetic properties origin from the exchange coupling between FeCo granules.3. For the typical sample of x= 0.67 without any anneal processing, coercivities in hard and easy axes are 1.43 and 7.08 Oe, respectively,4πMs is equal to 9.85 kGs, Hk is equal to 50.68 Oe and p reaches 2.06 x 103μΩcm, fr= 2.31 GHz, which imply that the FeCo-ZnO nano-granular films can be well applied in high frequency range.4. The measuredμ～f curves were fitted well with the solution of Landau-Lifshitz equations, implying that the mechanism can be ascribed to the natural resonance.5. For the typical sample of x= 0.67, the temperature coefficient of resistivity (TCR) is negative and satisfiesρ∞1/(?), which indicates that the mechanism of electronic transportation of the sample is weak localized electron-electron interaction.6. We study the relationship between the microstructure, magnetic properties of samples and sputtering power(P). The conclusions are as follows:the sputtering power dependence on the structure and Hce is low; 4πMs and fr increase and then decrease slightly with increasing P, Hk increase straight with increasing P. The typical sample of (Fe65Co35)0.67(ZnO)0.33 possesses high fr, low damping factor and high p, which indicate that excellent high frequency soft magnetic properties are obtained.This work proves the feasibility of preparing metal-semiconductor granular films and that excellent soft magnetic properties can be obtained in FeCo-ZnO thin films which imply the films can be applied in high frequency range.