Magnetic and electrical properties of ferromagnetic nanocomposites based on Co nanoparticles in Al2O3 matrix

Magnetic, structural, and electrical properties are reported for ferromagnetic nanocomposites (FMNC) consisting of nanometer size Co ferromagnetic nanoparticles (NP) embedded in Al2O3 dielectric matrix. Cox(Al2O3)(100-x) FMNC with x = 7.8, 28.2, and 42.2 at.% were obtained in the form of (1-5) mu m thick films by modified electron beam physical vapor deposition of Al2O3 and Co vapors condensing on policor substrate at temperatures 100-400 degrees C. Magnetic properties of these FMNC studied by SQUID magnetometry and ferromagnetic resonance (FMR) methods revealed paramagnetic properties for layers with x = 7.8 at.%, superparamagnetic behavior for x = 28.2 at.%, and ferromagnetic state for the highest Co concentration studied x = 42.2 at.%. Temperature dependence of electrical conductivity in FMNC with low Co content was found to follow the Mott law for variable range hopping mechanism. Magnetic field dependence of resistivity revealed a negative magnetoresistance effect. These results confirm the effectiveness of the applied technology for the preparation of Cox(Al2O3)(100-x) FMNC. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim