Dresden 2003 – scientific programme
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MA: Magnetismus
MA 14: Poster: Schichten(1-31), Spinabh.Trsp.(32-47), Exch.Bias(48-54), Spindyn.(55-64), Mikromag.(65-76), Partikel(77-88), Oflmag.(89-92), Spinelektr.(93-98), Elektr.Theo.(99-103), Mikromag+PhasÜ+Aniso.(104-122), MagnMat.(123-134), Messm+Mol-Mag.(135-139), Kondo(140-151)
MA 14.106: Poster
Tuesday, March 25, 2003, 15:15–19:15, Zelt
A lower bound for the volume-averaged mean-square magnetostatic stray field — •Andreas Michels1,2, Jörg Weissmüller1,2, and Rainer Birringer2 — 1Institut für Nanotechnologie, Forschungszentrum Karlsruhe, Karlsruhe, Germany — 2Technische Physik, Universität des Saarlandes, Saarbrücken, Germany
Based on a micromagnetics model, we develop a method through which quantitative information on the volume-averaged mean-square magnetostatic stray field ⟨ |Hdb|2 ⟩v due to non-zero divergences of the magnetization M within the bulk of a ferromagnetic body can be obtained by analysis of magnetic-field-dependent small-angle neutron scattering data. In the limit of high applied magnetic field Ha, when the direction of M deviates only sligthly from Ha, we have estimated a lower bound for ⟨ |Hdb|2 ⟩v as a function of the external field, and we have applied the method to bulk samples of nanocrystalline (nc) electrodeposited Ni and Co and coarse-grained polycrystalline cold-worked Ni. The root-mean-square magnetostatic stray field, which is inherent to a particular magnetic microstructure, shows a pronounced field dependence, with values ranging from about 5 to 50 mT. Even at applied fields as large as 1.7 T, the quantity µ0 ⟨ |Hdb|2 ⟩v1/2 of nc Co is still 24 mT, which suggests that contributions to the total magnetostatic field originating from the bulk are significant in nc ferromagnets; therefore, ⟨ |Hdb|2 ⟩v cannot be ignored in the interpretation of e.g. measurements of magnetization or spin-wave resonance. A comparison of ⟨ |Hdb|2 ⟩v with the volume-averaged mean-square anisotropy field reveals that both quantities are of comparable magnitude. [Ref.: Eur. Phys. J. B 29, 533-540 (2002).]