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Magnetic nanocomposites (MNC), in which nanoparticles of ferromagnetic metals are distributed in wide-gap dielectric matrices (Al2O3 or SiO2), are prospective materials for electronics due to their amenability to technological control of the concentration and size of ferromagnetic nanoparticles. Co/Al2O3 and Co/SiO2 MNC layers with Co concentrations below the percolation threshold were deposited on polycor substrates using electron-beam deposition in a vacuum (EB-PVD). Scanning electron microscopy showed the presence of tightly packed Co grains of irregular shape with sizes of 5–50 nm in MNC. Low-temperature measurements of the magnetization for MNC Co/Al2O3 were made in the temperature range 4–300 K and magnetic fields up to 10 kOe. The 'magnetic exchange bias' has been detected, and it increases with a rise in Co concentration. By studying the electrical properties of the MNC Co/Al2O3 and Co/SiO2 in the temperature range of 77–280 K, the Mott type electron transport hopping mechanism was established. We first observed the effect of a giant positive thermoelectric power in a magnetic field in MNC Co/Al2O3 and the effect of a negative magnetothermoelectric power in a Co/SiO2. [ABSTRACT FROM AUTHOR]

For the first time, in ferromagnetic nanocomposites Co/oO/Al2O3 formed by two-crucible electron beam evaporation with deposition on a policor substrate, the magnetic exchange bias was observed. It is associated with the magnetic interaction of the ferromagnetic metal core of Co nanoparticles with antiferromagnetic CoO layer on their surface. The low value of magnetic exchange bias is attributed to the small thickness of the CoO shell, inasmuch as the energy of exchange magnetic anisotropy, which decreases with diminishing the antiferromagnetic CoO layer thickness, cannot provide a significant increase of the coercive force when changing the magnetic field direction. The ferromagnetic nanocomposites with the magnetic exchange bias can be used as a bias magnetic layer for magnetoresistive sensors. [ABSTRACT FROM AUTHOR]

In nanocomposite layers consisting of Co nanoparticles in Al2O3 matrix the thermoelectric power was studied in a wide range of Co content. These layers revealed the giant thermoelectric power in a magnetic field for Co content below percolation threshold. This unusual phenomenon has been explained by hopping electron transport through the media which consist of both, nonmagnetic and magnetic centers in the conditions of temperature gradient. [ABSTRACT FROM AUTHOR]

Magnetic nanocomposites (MNC), in which nanoparticles of ferromagnetic metals are distributed in wide-gap dielectric matrices (Al2O3 or SiO2), are prospective materials for electronics due to their amenability to technological control of the concentration and size of ferromagnetic nanoparticles. Co/Al2O3 and Co/SiO2 MNC layers with Co concentrations below the percolation threshold were deposited on polycor substrates using electron-beam deposition in a vacuum (EB-PVD). Scanning electron microscopy showed the presence of tightly packed Co grains of irregular shape with sizes of 5–50 nm in MNC. Low-temperature measurements of the magnetization for MNC Co/Al2O3 were made in the temperature range 4–300 K and magnetic fields up to 10 kOe. The 'magnetic exchange bias' has been detected, and it increases with a rise in Co concentration. By studying the electrical properties of the MNC Co/Al2O3 and Co/SiO2 in the temperature range of 77–280 K, the Mott type electron transport hopping mechanism was established. We first observed the effect of a giant positive thermoelectric power in a magnetic field in MNC Co/Al2O3 and the effect of a negative magnetothermoelectric power in a Co/SiO2. [ABSTRACT FROM AUTHOR]