Berlin 2008 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 7: Micro and Nanostructured Magnetic Materials II
MA 7.3: Vortrag
Montag, 25. Februar 2008, 15:45–16:00, EB 301
Two distinct reversal modes in ordered arrays of magnetic iron oxide nanotubes prepared by atomic layer deposition — •Julien Bachmann1,2, Jing Jing1, Juan Escrig1,3, Dora Altbir3, Sven Barth4, Sanjay Mathur4, Ulrich Goesele1, and Kornelius Nielsch2 — 1Max Planck Institute of Microstructure Physics, Halle — 2Institute of Applied Physics, University Hamburg — 3Departamento de Fisica, Universidad de Santiago de Chile — 4Institute of Inorganic Chemistry, University Wuerzburg
Ordered arrays of Fe3O4 nanotubes have been prepared by atomic layer deposition (ALD) in a structured substrate used as template, porous anodic alumina. With these tools, the length, diameter, and wall thickness of the tubes can be tuned accurately between 1 and 5 µ m, between 40 and 160 nm, and between 1 and 40 nm, respectively. This enables one to systematically study how physical properties are affected by geometry. Such arrays give rise to a ferromagnetic response that strongly depends on geometry. Variations of the tube wall thickness result in non-monotonic changes in coercive field. Theoretical modeling of the magnetization reversal between the two magnetically saturated states reproduces the experimental data. For thin tubes the reversal occurs by propagation of a "vortex" domain boundary, while in thicker ones it is driven by propagation of a "transverse" domain boundary. The optimal wall thickness thus corresponds to the crossover between the vortex and transverse modes of magnetization reversal. We envision that the method may be generalized to nanoobjects of more complex geometries.