Fizika Nizkikh Temperatur: Volume 45, Number 2 (February 2019), p. 263-269 ( to contents , go back )
Nontrivial phenomena in magnetic nanocomposites Co/Al2O3 and Co/SiO2
G.V. Lashkarev, M.V. Radchenko, A.E. Baibara, M.E. Bugaiova, L.I. Petrosian
I. Frantsevich Institute for Problems of Materials Science NAS str. Wilde, 5, Chernivtsi, 58001, Ukraine
Laboratoire GEMaC, University of Versailles St. Quentin en Yvelines, Versailles, France
T. Story, W. Knoff, N. Nedelko, A. Ślawska-Waniewska, and M. Foltyn
Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, Warsaw, Poland
Y.A. Stelmakh, and L.A. Krushynskaya
E.O.Paton Electric Welding Institute 66 Antonovich str., Kiev, 03150, Ukraine
Received October 11, 2018, published online December 20, 2018
Magnetic nanocomposites (MNC), in which nanoparticles of ferromagnetic metals are distributed in a wide-gap dielectric matrixes (Al2O3 or SiO2), are perspective materials for electronics due to the ability to give them necessary properties by 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 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 Co concentration growing. By studying the electrical properties of the MNC Co/Al2O3 and Co/SiO2 in the temperature range of 77–280 K, 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.
Key words: EB-PVD, magnetic nanocomposites, Co nanoparticles, magnetic exchange bias, magnetothermoelectric power.