Structural and magnetic properties of TM-SiO2 (TM = Fe, Co, Ni) films

TMx-(SiO2)(1-x) (TM =Fe, Co, Ni) thin films were prepared in a wide concentration range (0.35 less than or equal to x less than or equal to 1). Structure was Studied with transmission electron microscopy (TEM), X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). Magnetic and magnetotransport properties were investigated by means of magnetization and Hall effect measurements. TEM images display nanometric spherical structures embedded in a SiO2 amorphous matrix, with typical sizes increasing from 3 to 5 nm when TM volume concentration x is increased. SAXS measurements indicate a complex structure formed by nanosized objects. XRD measurements show that the structure is composed by amorphous SiO2 and TM crystallites. Slightly above the percolation threshold all samples display giant Hall effect. The observed magnetic properties are dependent on x, and display an evolution resulting from the progressive increase of the mean particle size. (C) 2003 Elsevier Science B.V. All rights reserved.