Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 6: Magnetic Particles/Clusters II
MA 6.7: Talk
Monday, March 26, 2007, 16:45–17:00, H10
Improved kinetics of the phase transformation of FePt nanoparticles from fcc to fct by ion irradiation — •Andreas Klimmer1, Ulf Wiedwald1, Birgit Kern1, Luyang Han1, Kai Fauth2, Hans-Gerd Boyen1, and Paul Ziemann1 — 1Institut für Festkörperphysik, Universität Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany — 2Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart, Germany
Fe50Pt50 alloy nanoparticles are promising candidates for ultra high density data storage due to their huge magnetic anisotropy energy in the chemically ordered L10 phase (fct). Starting from chemically disordered particles in fcc phase, the transformation into the chemically ordered fct phase is obtained by annealing at typically 600∘ - 800∘ C. We present experiments on arrays of Fe51Pt49 fcc nanoparticles (diameter 7 nm, inter-particle distances 60 nm), which were prepared using a micellar technique. The particles were irradiated with 350 keV He+ ions up to 1016 ions/cm2 at room temperature. Using XMCD measurements the transformation into the chemically ordered L10 phase can be extracted from the hysteresis in the magnetisation curves. A comparison of irradiated and non-irradiated samples reveals improved kinetics of the phase transformation of the ion irradiated nanoparticles. Thus coercive fields of 330 Oe at 300 K were obtained after 600∘ C annealing temperature for the irradiated particles, whereas the unirradiated ones still show superparamagnetic behaviour under identical annealing conditions.