Size effects in ordered arrays of magnetic nanotubes: Pick your reversal mode.

Ordered arrays of magnetic nanotubes are prepared by combining a porous template (anodic alumina) with a self-limiting gas-solid chemical reaction (atomic layer deposition). The geometric parameters can thus be tuned accurately (tube length of 1–50 μm, diameter of 20–150 nm, and wall thickness of 1–40 nm), which enables one to systematically study how confinement and anisotropy effects affect the magnetic properties. In particular, the wall thickness of such ordered Fe3O4 nanotubes has a nonmonotonic influence on their coercive field. Theoretical models reproduce the size effects that are experimentally observed and interpret them as originating from a crossover between two distinct modes of magnetization reversal. [ABSTRACT FROM AUTHOR]