Neutron scattering on magnetic nano-objects

Abstract

1. MAGNETIC NANOSTRUCTURES During the last 20 years, the field of the magnetism of nanostructures has exploded. A huge number of new magnetic structures have appeared in which the nanometer scale plays a key role. It is possible to classify them into 3 categories: -In 3 dimensions, it is possible to identify a wide range of systems such as (i) nanoparticles in solutions forming ferrofluids, (ii) percolating phases as found in manganites for example, (iii) magnetic domains or domain walls in crystals, (iv) long range helical structures as found in MnSi or BiFeO 3 for example. These objects are ideally studied using Small Angle Neutron Scattering (SANS) which enable measuring either the shape of individual objects (form factor) or their long range organization (structure factor). -In 2 dimensions, nanometer size objects organized on surfaces. These objects can be either produced by lithography techniques or by self-organization processes. The scattering technique which can be used is either SANS or Grazing Incidence SANS. -In 1 dimension, thin films produced by physical means such as vacuum deposition (sputtering, evaporation, laser ablation ...): metal thin films, oxide thin films, magnetic semi-conductors. These systems are most ideally studied by polarized neutron reflectivity. This is the object of a dedicated chapter. In this chapter we describe in a first part the basics of SANS scattering applied to the study of magnetic nano-objects. This is illustrated by a few examples of recent studies on magnetic nanoparticles and phase separated materials. In a second part we discuss the GISANS technique and illustrate its use in the case of the study of self-organized magnetic domains.