Berlin 2008 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 22: Magnetic Particles / Clusters II
MA 22.8: Vortrag
Mittwoch, 27. Februar 2008, 15:45–16:00, H 1028
Magnetic Anisotropy as Function of Particle Diameter in FePt Alloy Particles — Ulf Wiedwald1, Luyang Han1, Andreas Klimmer1, Balati Kurbanjan1, Lianchen Shan1, Hans-Gerd Boyen1, Kai Fauth2, and •Paul Ziemann1 — 1Institut für Festkörperphysik, Universität Ulm, Germany — 2Max-Planck-Institut für Metallforschung, Stuttgart, Germany
FePt alloy nanoparticles show huge magnetic anisotropy energy (MAE) in the chemically ordered L10 phase. The ordered phase is typically reached by annealing above 900 K starting from chemically disordered FePt nanoparticles [1]. The plasma-induced nucleation of metal salt loaded reverse micelles allows the formation of self-assembled regular arrays on top of various substrates. Employing the micellar preparation route, the particle separation can be tuned between 20-100 nm and, thus, agglomeration during annealing is fully suppressed [2]. We investigated the formation of the L10 phase as functions of annealing temperature and time for 3-10 nm FePt particles. The phase transformation is tracked by hysteresis loops at 11 K and 300 K. 9 nm particles are ferromagnetic at 300 K and a MAE of 1−2 · 106 J/m3 is found after annealing at T = 1000 K. Despite an increasing MAE as a function of annealing temperature is observed for particles smaller than 6 nm, those, however, remain superparamagnetic at 300 K.
[1] U. Wiedwald et al., Appl. Phys. Lett. 90, 062508 (2007)
[2] A. Ethirajan et al., Adv. Mater. 19, 406 (2007)
*New address: H.-G. Boyen, University of Hasselt, Belgium