Lesnik N. The study of static, microwave, relaxation characteristics and magnetic anisotropy of low dimensional magnets in a correlation with their microstructure

A study of magnetic characteristics of nanomaterials, based on 3d - ferromagnets, depending on their microstructure has been carried out using combined FMR-NMR, structural and magnetometric techniques. Single-layer continuous films having different degrees of the short-range order, magnetic multilayers and systems with two- or three-dimensional networks of magnetic granules, embedded either in non-magnetic metallic or insulating matrix, have been investigated. The effect of structural inhomogeneities such as film and nanoparticle surfaces, multilayer interfaces, grain boundaries, and the irregular atom distribution in alloys on magnetization reversal, effective anisotropy fields, the FMR linewidth, hyperfine fields and nuclear relaxation rates in heterogeneous films was studied in wide ranges of the frequency and temperature. The new information about mechanisms of interactions between magnetic sublayers as well as among magnetic nanoparticles, has been obtained. By studying a percolation process, it has been shown that an assembly of superparamagnetic granules reveals ferromagnetic behaviour just below the structural percolation. The nature of both the oblique and in-plane anisotropies in granular films, as well as the perpendicular anisotropy in nanocrystalline Ni films has been cleared up. All the aforecited results are new and they further clarify behaviour of nanomagnets upon applied magnetic fields and a temperature.