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MA: Fachverband Magnetismus

MA 6: Magnetic Particles/Clusters II

MA 6.7: Vortrag

Montag, 26. März 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.