Abstract

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 Fe3 O4 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. © 2009 American Institute of Physics.