References of "Wiedenmann, A"
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See detailSmall-angle Neutron Scattering with One-dimensional Polarization Analysis
Michels, Andreas UL; Honecker, Dirk UL; Döbrich, Frank UL et al

in Neutron News (2011), 22(3), 15-19

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See detailNeutron spin-flip scattering of nanocrystalline cobalt
Honecker, Dirk UL; Döbrich, Frank UL; Dewhurst, C. D. et al

in Journal of Physics : Condensed Matter (2011), 23(1), 1-4

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See detailLongitudinal polarization analysis in small-angle neutron scattering
Honecker, Dirk UL; Ferdinand, A.; Döbrich, Frank UL et al

in European Physical Journal B -- Condensed Matter (2010), 76(2), 209-213

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See detailOne-D neutron-polarization analysis on magnetic nanostructures
Honecker, Dirk UL; Ferdinand, A.; Döbrich, Frank UL et al

in Europhysics News (2010), 41(5), 15-15

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See detailSpin structure of nanocrystalline terbium
Weissmüller, J.; Michels, Andreas UL; Michels, D. et al

in Physical Review. B, Condensed Matter and Materials Physics (2004), 69

We present an experimental study of the magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent small-angle neutron scattering (SANS) data are analyzed quantitatively in terms of ... [more ▼]

We present an experimental study of the magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent small-angle neutron scattering (SANS) data are analyzed quantitatively in terms of the correlation function of the spin misalignment. We find that up to applied fields of several tesla the magnetization remains “locked in” to the basal planes of the hcp crystal lattice of each individual crystallite, but that the in-plane orientation of the spins is highly nonuniform within each grain. This spin disorder at the nanoscale can be suppressed by a large applied field, but in the remanent state the disorder reduces the magnetization to values considerably below the Stoner limit. In field-dependent SANS, the intragrain spin disorder gives rise to a crossover of the scattering curves, and to the unusual finding that the scattering cross section at small scattering vector increases with increasing magnetic field. As the origin of the internal spin disorder within the grains, we propose an extra magnetic anisotropy energy at small grain size, presumably due to microstrain, a suggestion which is supported by analysis of ac-susceptibility data in the paramagnetic state. Our finding of a reduced remanence at small grain size is contrary to the remanence enhancement that is observed in other nanocrystalline hard magnets. We also report an unusual logarithmic field dependence of the magnetization over wide ranges of the applied field and temperature. [less ▲]

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See detailMagnetic microstructure and properties of the nanocrystalline hard magnet terbium
Weissmüller, J.; Michels, D.; Michels, Andreas UL et al

in Physica Status Solidi A. Applied Research (2002), 189

We present an experimental study of the magnetic properties and magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent small-angle neutron scattering (SANS) data suggest that up to ... [more ▼]

We present an experimental study of the magnetic properties and magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent small-angle neutron scattering (SANS) data suggest that up to applied fields of several Tesla the magnetization remains locked in to the basal planes of the hcp crystal lattice of each individual crystallite; as a consequence, domain-wall movement along the basal planes is eliminated as a mechanism for magnetization reversal, and the coercive field is substantially increased. [less ▲]

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See detailAnalysis of the small-angle neutron scattering of nanocrystalline ferromagnets using a micromagnetics model
Weissmüller, J.; Michels, Andreas UL; Barker, J. G. et al

in Physical Review. B, Condensed Matter and Materials Physics (2001), 63

In ferromagnets with a nonuniform magnetocrystalline and/or magnetoelastic anisotropy, such as nanocrystalline (nc-) or cold-worked (cw-) polycrystalline materials, the static magnetic microstructure ... [more ▼]

In ferromagnets with a nonuniform magnetocrystalline and/or magnetoelastic anisotropy, such as nanocrystalline (nc-) or cold-worked (cw-) polycrystalline materials, the static magnetic microstructure gives rise to strong elastic magnetic small-angle neutron scattering (SANS). The paper explores a method for analyzing field-dependent SANS data from such materials in terms of a model based on the theory of micromagnetics. Samples of cw Ni and of electrodeposited nc Ni and nc Co were characterized by x-ray scattering and magnetometry, and were investigated by SANS both with and without polarization of the neutron beam. The variation of the differential scattering cross section with the scattering vector and with the applied magnetic field is well described by the model. Also, experimental results for the exchange stiffness constant A and for the spin-wave stiffness constant D obtained from the analysis are found to agree with literature data obtained by inelastic neutron scattering on single-crystal specimens. The model supplies an “anisotropy field scattering function” that contains information on the magnitude of the magnetic anisotropy in the material, and on the characteristic length scales on which the anisotropy changes direction. The results suggest that the anisotropy may be strongly nonuniform in each crystallite, possibly due to twinning, and that some magnetic moments in the Ni samples are strongly pinned at defects. [less ▲]

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See detailMagnetic small-angle neutron scattering by nanocrystalline terbium
Weissmüller, J.; Michels, D.; Michels, Andreas UL et al

in Scripta Materialia (2001), 44(8), 2357-2361

We present an experimental study of the magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent SANS data are analyzed quantitatively in terms of the correlation function of the ... [more ▼]

We present an experimental study of the magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent SANS data are analyzed quantitatively in terms of the correlation function of the spin misalignment. We find that up to applied fields of several Tesla the magnetization remains ‘locked in’ to the basal planes of the hcp crystal lattice of each individual crystallite; But that the in-plane orientation of the spins is highly nonuniform within each particle. This internal structure can be suppressed by the applied field. [less ▲]

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See detailExchange-stiffness constant in cold-worked and nanocrystalline Ni measured by elastic small-angle neutron scattering
Michels, Andreas UL; Weissmüller, J.; Wiedenmann, A. et al

in Journal of Applied Physics (2000), 87(9), 5953-5955

We present a new method for determining the exchange-stiffness constant A of a ferromagnetic bulk material by field-dependent elastic small-angle neutron scattering (SANS). In the limit of high applied ... [more ▼]

We present a new method for determining the exchange-stiffness constant A of a ferromagnetic bulk material by field-dependent elastic small-angle neutron scattering (SANS). In the limit of high applied magnetic field H, for which the scattering volume is a single magnetic domain and the magnetization is nearly aligned with the direction of the applied field, a combination of micromagnetics theory with neutron scattering formalism suggests closed-form expressions for the differential scattering cross section as a function of the scattering vector and of H. Based on these results it is suggested that the exchange-stiffness constant can be extracted from experimental SANS data recorded as a function of H. At ambient temperature we have applied this method to polycrystalline cold-worked Ni and nanocrystalline electrodeposited Ni, finding exchange-stiffness constants of (8.2±0.2)×10−12 and (7.6±0.3)×10−12  J/m, respectively. Measurement at 5 K yields a value of (9.2±0.2)×10−12 J/m for the nanocrystalline sample, a temperature dependence that agrees qualitatively with data in the literature. In addition to the value of A, the technique supplies information on the spatial structure of the magnetic anisotropy field. [less ▲]

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See detailMeasuring the exchange-stiffness constant of nanocrystalline solids by elastic small-angle neutron scattering
Michels, Andreas UL; Weissmüller, J.; Wiedenmann, A. et al

in Philosophical Magazine Letters (2000), 80

In ferromagnets with a non-uniform magnetocrystalline and/or magnetoelastic anisotropy, such as nanocrystalline or cold-worked polycrystalline materials, the static magnetic microstructure gives rise to ... [more ▼]

In ferromagnets with a non-uniform magnetocrystalline and/or magnetoelastic anisotropy, such as nanocrystalline or cold-worked polycrystalline materials, the static magnetic microstructure gives rise to elastic magnetic small-angle neutron scattering (SANS). The paper explores a method for determining the exchange-stiffness constant A by analysis of the dependence of the elastic SANS cross-section on the applied magnetic field. Experimental results for A and for the spin-wave stiffness constant D in cold-worked or nanocrystalline Ni and Co are found to agree with literature data obtained by inelastic neutron scattering on single-crystal specimens. [less ▲]

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