Low Temperature Physics: 46, 792 (2020); https://doi.org/10.1063/10.0001542
Magnetotransport properties of nanogranular composites with low field positive magnetoresistance
M.M. Kulik1,2, S.M. Ryabchenko1, and A.V. Bodnaruk1
1Institute of Physics of the National Academy of Sciences 46 Nauki Ave., Kiev 03028, Ukraine
2Nanostructure Physics, Royal Institute of Technology, Stockholm 10691, Sweden
Received March 25, 2020, published online June 22, 2020
In nanogranular magnetic films with perpendicular anisotropy, which have a low-field positive magnetoresistance, a low-temperature feature was previously detected: during the first magnetization of a pre-demagnetized sample this magnetoresistance was observed but was absent in time of removing of the magnetic field and/or in time of subsequent magnetizations. The nature of this phenomenon has not been previously discussed and explained. In this paper, we studied the mentioned effect in a film of Co metal nanogranules in an Al2On insulating matrix with n close to 3. It is established that in this film, along with perpendicular anisotropy, there is in-plane anisotropy with the randomly oriented local light axes, which nevertheless, blocks the reorientation of the projections of the magnetic moments of the granules in the film plane below a certain temperature Tb. As a result, the restoration of the local short-range order in the orientation of the magnetic moments of the neighboring granules of the demagnetized film, which is optimal for conductivity, and which is destroyed by the introducing of a magnetic field, is blocked at temperatures below this Tb and is not restored during subsequent cycles of introducing and removing of the magnetic field without heating to T > Tb.
Key words: magnetization reversal processes, nanogranular magnetic films, positive magnetoresistance.