NANOCOMPOSITE (Fe,Ni) - SiO{sub}2 THIN FILMS CLOSE TO THE PERCOLATION THRESHOLD: MICROSTRUCTURAL AND MAGNETOTRANSPORT PROPERTIES

摘要

Granular ferromagnetic - insulator thin films consist of nanometer size ferromagnetic particles embedded in an insulating medium. They display a wide variety of magnetic and transport properties related to their unique nanostructure. Close to the percolation threshold they exhibit giant extraordinary Hall effect and nonlinear transport. In this paper some experimental results concerning the influence of the annealing temperature and compositions close to the percolation threshold on the microstructural and magnetotransport properties of (Fe{sub}20Ni{sub}80){sub}x-(SiO{sub}2){sub}(1-x) thin films are presented. The (Fe{sub}20Ni{sub}80){sub}x-(SiO{sub}2){sub}(1-x) thin films with metal content values between about 40% and 70% were deposited by R.F. sputtering technique from composite target. The samples were deposited on various substrates depending on the intended measurements. The (Fe{sub}20Ni{sub}80){sub}x-(SiO{sub}2){sub}(1-x) were thermally treated in vacuum at temperatures between at 300 and 400°C. The structural properties of the thin films are analysed by X-ray diffraction and morphology was investigated by transmission electron microscopy. The Hall voltage measurements were made at room temperature, by the van der Pauw method. Our results show that the microstructural and transport properties of the (Fe{sub}20Ni{sub}80){sub}x-(SiO{sub}2){sub}(1-x) thin films vary with composition and annealing temperature. At the percolation threshold we have evidentiated the crucial changes in the microstructure and Hall voltage values.