Magnetism of Nanometer-Sized Particles and Clusters

Abstract

Since the late 1940s, nanometer-sized magnetic particles have generated continuous interest as the study of their properties has proved to be scientifically and technologically very challenging. In particular it was recognised that the ferromagnetic state, with a given orientation of the particle moment, has a remanent magnetisation if the particle is small enough. This was the starting point of huge permanent magnets and magnetic recording industries. However, despite intense activity during the last few decades, the difficulties in making nanoparticles of good enough quality has slowed the advancement of this field. As a consequence, for 50 years, these applications concentrated above and then near the micrometer scale. In the last few years, this has no longer been the case because of the emergence of new fabrication techniques which have led to the possibility of making small objects with the required structural and chemical qualities. In order to study these objects new techniques were developed such as magnetic force microscopy, magne- tometry based on micro-Hall probes or micro-SQUIDs. This led to a new understanding of the magnetic behaviour of nanoparticles, which is now very important for the development of new fundamental theories of magnetism and in modelling new magnetic materials for permanent magnets or high density recording.