Nuclear magnetic resonance investigations of the structure and magnetic properties of metallic multilayers and nanocomposites

Abstract

As a probe of the short-range chemical and topological order, nuclear magnetic resonance (NMR) has proved useful to investigate the nanostructure of magnetic multilayers or granular systems and, in particular, to evaluate the nature, sharp or diffuse, of interfaces in such nanocomposites. These structural aspects are shortly reviewed in the paper. A larger emphasis is given to the magnetic properties that are accessed by the technique. As a first output of an NMR experiment in ferromagnets, the hyperfine field gives a direct insight on the local magnetization. Hence, for example, one can estimate the magnetization profile at a diffuse interface between a magnetic and nonmagnetic phase. In addition, NMR can probe selectively the magnetic anisotropy or exchange energy in different parts of a composite sample. Therefore NMR is a unique tool to investigate the correlation, at a local scale, between the nanostructure and the magnetic properties of a sample. For example, one can evidence the different magnetic hardness of the interface and bulk moments in multilayers, or of the magnetic clusters and alloyed regions in nanogranular alloys. Some relevant results are presented, which have been obtained in the course of investigations of Co-based multilayers, ultrathin films and granular systems.