Regensburg 2004 – wissenschaftliches Programm
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MA: Magnetismus
MA 13: Poster:Schichten(1-23),Spinabh.Trsp(24-41),Exch.Bias(42-56),Spindyn.(57-67),Mikromag.(68-76),Partikel(77-90),Spinelektr.(91-97),Elektr.Theo.(98-99),Mikromag+PhasÜ+Aniso.(100-105),Magn.Mat.(106-118),Messmethod.(119-121),Obflm.+Abbverf.(122-123)
MA 13.81: Poster
Dienstag, 9. März 2004, 15:00–19:00, Bereich A
Magnetization of fcc FexPt1−x nanoparticles: from Langevin to Stoner-Wohlfarth behaviour — •Frank Wiekhorst and Jürgen Kötzler — Institut f. Angewandte Physik, Univ. Hamburg, D-20355 Hamburg
We present field-dependent magnetizations of chemically disordered nanocrystals, d = 4 mm, imbedded in an organic matrix, recorded between 350 K and 5 K. Taking into account an effective uniaxial anisotropy, the temperature dependence of which has been determined by FMR [1] and by low-frequency absorption in zero field, we are able to describe quantitatively the crossover from isotropic Langevin behaviour, via anisotropic superparamagnetism [2], to the hysteretic regime below the blocking temperature. Our model considers the effects of anisotropy on both the equilibrium and non-equilibrium magnetization in a consistent way and involves the averaging upon randomly distributed axes. Possible origins of the temperature dependent anisotropy are discussed.
[1] F. Wiekhorst et al., Proc. ICM 2003, Rome, J.Magn.Magn. Mat., accepted
[2] F. Wiekhorst et al., Phys. Rev. B 67, 224416 (2003)