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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 μ m , 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 Fe <sub>3</sub> O <sub>4</sub> 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.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: In this chapter we present a theoretical study of magnetic ground states, domain walls and magnetization reversal process in nanomagnets with cylindrical symmetry. It is well known that macroscopic ferromagnets are organized in domains, and nearest domains are separated by domain walls, whose typical sizes are comparable with the dimensions of typical magnetic nanostructures. On the other hand, when the dimensions of a nanomagnet are in the range of the exchange length of the magnetic material, we can expect a single-domain behavior. As particle size increases, dipolar interactions become more and more important, and the magnetic ground states start deviating from single domain, forming magnetic structures like vortex, flower, leaf and onion states as a function of their geometry. These magnetic states are the result of competition between exchange coupling, dipolar interactions, and anisotropy. We also present current research on magnetization reversal processes in nanodots and nanotubes, where we show that vortex-like structures play a crucial role in the magnetic switching of ferromagnetic nanoparticles.
01/2008: pages 237-260; , ISBN: 978-81-7895-373-1
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ABSTRACT: The magnetic properties of nanorings consisting of alternate layers of magnetic and non-magnetic materials are studied. The relative stability of the different magnetic configurations is examined as a function of the ring geometry. The interactions between the magnetic layers play an important role which is evidenced in the phase diagrams presented.
International Journal of Nanotechnology 06/2007; 4(5):531-540. · 1.01 Impact Factor
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ABSTRACT: The magnetic properties of nanorings consisting of alternate layers of magnetic and non-magnetic materials are studied. The relative stability of the different magnetic configurations is examined as a function of the ring geometry. The interactions between the magnetic layers play an important role which is evidenced in the phase diagrams presented.
Int. J. Nanotechnol. Int. J. Nanotechnol. 01/2007; 4(4):531-540.
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JOURNAL OF APPLIED PHYSICS. 105(7).
