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Nontrivial Phenomena in Magnetic Nanocomposites Co/Al2O3 and Co/SiO2.

Authors :: Lashkarev, G. V.
Radchenko, M. V.
Baibara, A. E.
Bugaiova, M. E.
Petrosian, L. I.
Dumond, Y.
Story, T.
Knoff, W.
Nedelko, N.
Ślawska-Waniewska, A.
Foltyn, M.
Stelmakh, Y. A.
Krushynskaya, L. A.
Source :: Low Temperature Physics; Feb2019, Vol. 45 Issue 2, p228-233, 6p, 3 Black and White Photographs, 1 Diagram, 3 Charts, 7 Graphs
Publication Year :: 2019
Abstract: Magnetic nanocomposites (MNC), in which nanoparticles of ferromagnetic metals are distributed in wide-gap dielectric matrices (Al<subscript>2</subscript>O<subscript>3</subscript> or SiO<subscript>2</subscript>), are prospective materials for electronics due to their amenability to technological control of the concentration and size of ferromagnetic nanoparticles. Co/Al<subscript>2</subscript>O<subscript>3</subscript> and Co/SiO<subscript>2</subscript> 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/Al<subscript>2</subscript>O<subscript>3</subscript> 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/Al<subscript>2</subscript>O<subscript>3</subscript> and Co/SiO<subscript>2</subscript> 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/Al<subscript>2</subscript>O<subscript>3</subscript> and the effect of a negative magnetothermoelectric power in a Co/SiO<subscript>2</subscript>. [ABSTRACT FROM AUTHOR]