Browsing by Author "Michels, A"

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    Exchange-stiffness constant of a Nd-Fe-B based nanocomposite determined by magnetic neutron scattering
    (American Institute of Physics, 2013-09-16) Bick, JP; Suzuki, K; Gilbert, EP; Forgan, EM; Schweins, R; Lindner, P; Kubel, C; Michels, A
    We report magnetic-field-dependent small-angle neutron scattering (SANS) experiments on a Nd2Fe14B/Fe3B nanocomposite. For the two scattering geometries where the applied magnetic field is either perpendicular or parallel to the incoming neutron beam, we have independently analyzed the field-dependent SANS data in terms of micromagnetic theory, taking into account demagnetizing-field effects. The approach in reciprocal space is supported by an analysis of the data in real space and provides consistent results for the exchange-stiffness parameter and the mean magnetic anisotropy-field radius. © 2013, American Institute of Physics.
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    Experimental observation of magnetic poles inside
    (IOP Science, 2014-12-15) Périgo, EA; Gilbert, EP; Metlov, KL; Michels, A
    The pole-avoidance principle of magnetostatics results in an angular anisotropy of the magnetic neutron scattering cross section dΣM dΩ. For the case of a sintered Nd–Fe–B permanent magnet, we report the experimental observation of a ‘spike’ in dΣM dΩ along the forward direction. The spike implies the presence of long-wavelength magnetization fluctuations on a length scale of at least 60 nm. Using micromagnetic theory, it is shown that this type of angular anisotropy is the result of the presence of unavoidable magnetic poles in the bulk of the magnet and is related to the q ≠ 0 Fourier modes of the magnetostatic field. Thus, our observation proves the existence of such modes.© 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    Magnetization reversal in Nd-Fe-B based nanocomposites as seen by magnetic small-angle neutron scattering
    (American Institute of Physics, 2013-01-14) Bick, JP; Honecker, D; Dobrich, F; Suzuki, K; Gilbert, EP; Frielinghaus, H; Kohlbrecher, J; Gavilano, J; Forgan, EM; Schweins, R; Lindner, P; Birringer, R; Michels, A
    We have studied the magnetization-reversal process of a Nd2Fe14B/Fe3B nanocomposite using small-angle neutron scattering. Based on the computation of the autocorrelation function of the spin misalignment, we have estimated the characteristic size l(C) of spin inhomogeneities around the Nd2Fe14B nanoparticles. The quantity l(C) approaches a constant value of about 12.5 nm (similar to average Nd2Fe14B particle radius) at 14 T and takes on a maximum value of about 18.5 nm at the coercive field of -0.55 T. The field dependence of l(C) can be described by a model that takes into account the convolution relationship between the nuclear and the magnetic microstructure. © 2013, American Institute of Physics