Berlin 2005 – wissenschaftliches Programm
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MA: Magnetismus
MA 4: Mikromagnetismus / Computational Magnetism
MA 4.2: Vortrag
Freitag, 4. März 2005, 12:15–12:30, TU H1028
Ferromagnetic hollow nanoparticles — •D. Goll1, A.E. Berkowitz2, and H.N. Bertram2 — 1Max-Planck-Institut für Metallforschung, Stuttgart, Germany — 2Center for Magnetic Recording Research, La Jolla, USA
Single-domain nanoparticles are an important prerequisite for ultra-high density magnetic recording. Recently, ferromagnetic nanoparticles with a nonmagnetic core have been successfully produced by spark erosion and colloid chemistry methods. We have analytically calculated and compared the total magnetic energies of zero-field magnetization states of such particles to find out the conditions for single-domain behavior. Therefore, the size of the particles and the thickness of the spheroidal shell have been systematically varied for different hard and soft magnetic materials. From the micromagnetic calculations the corresponding phase diagrams of the lowest-energy configurations have been derived. The phase diagrams identify two phases which are for hard magnetic materials as Nd2Fe14B or FePt the single-domain state and the two-domain state. For soft and middle-hard magnetic materials as permalloy, Fe or Co the single-domain state and the curling-vortex state occurr. It turns out, that in the case of hard magnetic materials the critical diameter for which the single-domain state becomes energetically unfavorable can become more than doubled for ultrathin spheroidal shells compared to the corresponding bulk sphere. The magnetization reversal process takes place inhomogeneously starting at the magnetic poles of the inner surface. This project was sponsored by DAAD, Bonn.