Determining magnetization configurations and reversal of individual magnetic nanotubes

This chapter focuses on ferromagnetic nanotubes (FNTs) and their experimental investigation by techniques capable of measuring the response of individual specimens. This capability has developed recently and is now having a strong impact on our understanding of the behavior of real FNT structures. Despite the wealth of predictions on the equilibrium configurations and reversal modes of FNTs, direct experimental evidence of their magnetic behavior has emerged only recently. This is partly due to the difficulty of measuring individual magnetic nanostructures with many conventional magnetometry techniques, which do not have the necessary sensitivity to detect the small total magnetic moment of a single nanomagnet. As a result, measurements of their magnetic properties are often carried out on large ensembles, whose constituent nanomagnets have a distribution of size, shape, and orientation and-depending on the density-may interact with each other. These complications conspire to make accurate characterization of the stable magnetization configurations and reversal processes difficult. To obtain a clear understanding of the magnetic properties of FNTs, it is therefore advantageous to investigate individual specimens. We review such efforts, which include measurements of magnetoresistence, torque magnetometry, X-ray microscopy, scanning SQUID microscopy, and magnetic force microscopy.