Investigations of the magnetic properties of the granular system Co 0.6 ( Al 2 O n ) 0.4 possessing isotropic positive magnetoresistance

Magnetostatic, magnetoresonance (FMR), and magnetotransport measurements are performed in the temperature range 100 – 360 K in the granular ferromagnetic film Co 0.59 ( Al 2 O n ) 0.41 possessing isotropic (independent of the angle between the direction of the current and magnetization in the plane) positive magnetoresistance in magnetic fields ± 500 Oe are performed. It is established that this anomaly of the magnetoresistance is due to short-range order effects in the ordering imposed on the magnetic moments of granules in the absence of an external magnetic field by their dipole–dipole interaction. It is established that the blocking temperature of thermally activated re-orientations of the magnetic moments of the granules differs substantially with respect to the measurement time and the methods used for this investigation. It is about 200 K for magnetization measurements and exceeds 470 K for FMR and measurements of the magnetoresistance. It is shown that ferromagnetic resonance in the present system changes from the regime “independent resonance of individual clusters” to the regime “collective resonance of a system of magnetic granules in a film” when the direction of the magnetic field changes from in-plane to normal to the film.