Magnetic, Conducting, and Magnetic Conducting Properties of Composite Films (CoFeB+SiO2+N2) in the Temperature Range 2–400 K and Magnetic Fields of 0, 1, and 5 T

Abstract

Composite films with compositions [(CoFeB)x+(SiO2)(1–x)+N2), x = 0,33–0,52] were obtained by ion-beam sputtering using metal alloy and dielectric targets in a nitrogen atmosphere. The thickness and content of atomic elements, and the concentration of metal alloy x composite films were found using a TESCAN MIRA3 electron microscope. Images of the magnetic phase contrast of the surface of composite films were obtained using magnetic force microscopy (Integra Prima atomic force microscope NT-MDT, Russia) with an MFM10 cantilever. Magnetic phase contrast images of x = 0,48–0,52 films were studied. All the composite films have granular and percolation structures, the volume ratio of these structures varies depending on x. The percolation structure of films with high concentrations x > 0,48 manifested in the presence of extended isolated areas (more than 1 μm) of the accumulation of metal granules. The temperature dependences of magnetic susceptibility, specific conductivity, and specific magnetic conductivity of the composite films with metal alloy concentrations x = 0,33–0,52 were studied in a temperature range of 2–400 K and in magnetic fields of 0 T, 1 T, and 5 T. All measurements of magnetic susceptibility and electrical resistance of the composite films in this temperature and magnetic field range were carried out at the center for diagnostics of functional materials for medicine, pharmacology, and nanoelectronics at St. Petersburg State University. In composite film No. 1 (x = 0,46) in the temperature range 100–300 K, the highest positive magnetic conductivity had a value of 1,2 at 200 K. The highest positive magnetic conductivity (about 1,2) was observed in composite granular films with small granule sizes. The results of temperature studies of the magnetic conductivity of the composites show that the ratio of positive and negative magnetic conductivity depends on the temperature of the film and on the concentration of the metal alloy x, which sets the ratio of the granular and percolation structures. Large negative magnetic conductivity (about –0,2) occurs in composite films No. 3 and 5, the structure of which, along with the granular structure, includes extended (more than several micrometers) metallic areas of metal granules.