Low Temperature Physics: 33, 974 (2007); https://doi.org/10.1063/1.2747075 (13 pages)
Fizika Nizkikh Temperatur: Volume 33, Number 11 (November 2007), p. 1282-1297 ( to contents , go back )
Investigation of magnetic properties of Co0.6(Al2On)0.4 granular system with isotropic positive magnetoresistance
A.A. Timopheev, S.M. Ryabchenko, A.F. Lozenko, P.A.Trotsenko
Institute of Physics National Academy of Sciences of Ukraine, 46 Nauki Ave., Kiev 03028, Ukraine
O.V. Stogney, A.V. Sitnikov, and S.F. Avdeev
Воронежский государственный технический университет Московский проспект, 14, г. Воронеж, 394026, Россия
Received March 17, 2007
The magnetic properties of the Co0.59(Al2On)0.41 granular thin film exhibiting an isotropic positive magnetoresistance (IPMR), were investigated by dynamic (FMR), magnetostatic and magnetotransport techniques in a wide temperature range (100–360K). It is shown that the above anomaly of magnetoresistance is caused by the intergrain dipole interaction. The existence of this interaction leads to the ordering of magnetic moments of the granules and the formation of a short-range order (like in spin-glass systems) at H = 0. It is shown, that the blocking temperature of thermally activated reorientations of the granules magnetic moments differs essentially depending on characteristic measuring time for the techniques used in the studies. For the magnetostatic measurements the blocking temperature is about 200 K, while for the FMR technique it is higher than 470 K. It is shown, that FMR of the system studied modifies from the regime of «independent resonances of separate clusters (short-range ordered areas)» to a regime of «collective resonance of a system of magnetic granules in the film» with varying the magnetic field from the in-plane direction to the direction along the normal to the film.
PACS: 75.75.+a Magnetic properties of nanostructures;
Key words: magnetoresistance, ferromagnetic resonance, superparamagnetic state.