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See detailMicromagnetic simulation of magnetic small-angle neutron scattering from two-phase nanocomposites
Michels, Andreas UL; Erokhin, Sergey; Berkov, Dmitry et al

in Journal of Magnetism & Magnetic Materials (2014), 350

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See detailStoner–Wohlfarth model for the anisotropic case
de Campos, Marcos Flavio; da Silva, Fernanda Sampaio; Perigo, Elio Alberto UL et al

in Journal of Magnetism & Magnetic Materials (2013), 345

The Stoner–Wohlfarth (SW) model was calculated for the anisotropic case, by assuming crystallographical texture distributions as Gaussian, Lorentzian and cos n (alpha). All these distributions were tested ... [more ▼]

The Stoner–Wohlfarth (SW) model was calculated for the anisotropic case, by assuming crystallographical texture distributions as Gaussian, Lorentzian and cos n (alpha). All these distributions were tested and both Gaussian and cos n (alpha) give similar results for Mr/Ms above 0.8. However, the use of cosn (alpha) makes it easier to find analytical expressions representing texture.The Lorentzian distribution is a suitable choice for not wel laligned magnets, or magnets with a high fraction of misaligned grains. It is discussed how to obtain the alignment degree Mr/Ms directly from two measurements of magnetic remanence at the transverse and parallel directions to the alignment direction of the magnet .It is demonstrated that even the wel laligned magnets with Mr/Ms=0.96 present coercive field of 60–70% of the anisotropy field, depending on the chosen distribution.The anisotropic SW model was used for discussing hysteresis squareness. Improving the crystalographical texture, the loop squareness also increases. [less ▲]

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See detailSynthesis and characterization of uniaxial ferrogels with Ni nanorods as magnetic phase
Bender, Philipp; Günther, Annegret UL; Tschöpe, Andreas et al

in Journal of Magnetism & Magnetic Materials (2011), 323

In the present study, the rotation of magnetic nanorods in a soft hydrogel matrix induced by a homogeneous magnetic field is investigated. Magnetic nanorods of ≈151.2 nm length and ≈17.7 nm diameter are ... [more ▼]

In the present study, the rotation of magnetic nanorods in a soft hydrogel matrix induced by a homogeneous magnetic field is investigated. Magnetic nanorods of ≈151.2 nm length and ≈17.7 nm diameter are synthesized via current-pulsed electrodeposition of nickel into porous aluminum oxide-templates. The nanorods are processed towards a stable colloidal dispersion by dissolution of the alumina template in aqueous NaOH to which PVP (polyvinyl-pyrrolidone) is added as surfactant. These suspensions are used to prepare gelatine-based ferrogels of different shear modulus with either isotropic or uniaxial orientation-distribution of the nanorods. While magnetization measurements of rigid ferrogels mainly reflect the magnetic properties of the nickel nanorods, the magnetization behavior of soft ferrogels is significantly influenced by a field-induced rotation of the nickel nanorods in the low compliant matrix. A particular analysis of magnetization measurements on uniaxial ferrogels enables to quantify the rotation angle of the nanorods with respect to their initial orientation under the influence of a transversal homogeneous magnetic field. The analysis of the field-dependent rotation also allows to estimate the local shear modulus of the matrix which is demonstrated by an investigation of room temperature ageing process of the ferrogel. [less ▲]

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See detailAngular dependence of coercivity and remanence of Ni nanowire arrays and its relevance to magnetoviscosity
Günther, Annegret UL; Monz, S.; Tschöpe, A. et al

in Journal of Magnetism & Magnetic Materials (2008), 320(7), 1340-1344

Ni nanowire arrays with varying wire dimensions (diameter d, length l) and center-to-center distances dCC were synthesized by pulsed electrodeposition of Ni in porous Al templates. The magnetization ... [more ▼]

Ni nanowire arrays with varying wire dimensions (diameter d, length l) and center-to-center distances dCC were synthesized by pulsed electrodeposition of Ni in porous Al templates. The magnetization-reversal behavior of the arrays was investigated by means of magnetometry for different angles θ between the wire axes and the applied magnetic field. The functional dependences of the characteristic parameters coercivity HC(θ) and reduced remanence mR/mS(θ) exhibit a strong dependence on the wire dimensions and the center-to-center distance. For instance, for nanowire arrays with d=40 nm, dCC=100 nm, and for θ=0°, the coercivity takes on a rather large value of μ0HC=85 mT and mR/mS=94%; reducing dCC to 30 nm and d to 17 nm results in μ0HC=49 mT and mR/mS=57%, an observation which suggests an increasing magnetostatic interwire interaction at increased (d/dCC)-ratio. The potential application of nanowires as the constituents of ferrofluids is discussed. [less ▲]

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See detailSynthesis of a nanorod ferrofluid and characterisation by magnetic-field-dependent small-angle X-ray scattering
Döbrich, Frank UL; Michels, Andreas UL; Birringer, R.

in Journal of Magnetism & Magnetic Materials (2007), 316(e), 779-782

Compared to conventional ferrofluids, which contain mostly spherical particles, a dispersion of highly anisometric particles such as rods or chains is expected to give rise to an enhancement or ... [more ▼]

Compared to conventional ferrofluids, which contain mostly spherical particles, a dispersion of highly anisometric particles such as rods or chains is expected to give rise to an enhancement or modification of well-known ferrofluid properties. This contribution reports on the synthesis of a ferrofluid containing stable chains of iron nanoparticles and on its microstructural characterisation by means of transmission electron microscopy and small-angle X-ray scattering (SAXS). The SAXS measurements develop a pronounced anisotropy of the scattering pattern as a function of an increasing external magnetic field. Evaluation of the radially averaged SAXS curves in terms of basic scattering functions is discussed. [less ▲]

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See detailTemperature dependence of dipole-field scattering in Nanoperm
Michels, Andreas UL; Vecchini, C.; Moze, O. et al

in Journal of Magnetism & Magnetic Materials (2007), 316(2), 448-450

We present small-angle neutron scattering (SANS) data for the temperature variation of the recently observed dipole-field-induced spin-misalignment scattering in the soft magnetic nanocomposite Nanoperm ... [more ▼]

We present small-angle neutron scattering (SANS) data for the temperature variation of the recently observed dipole-field-induced spin-misalignment scattering in the soft magnetic nanocomposite Nanoperm (Fe89Zr7B3Cu1). The associated clover-leaf-shaped angular anisotropy of the SANS pattern, which is due to spin disorder arising from dipolar stray fields of the iron nanoparticles, persists up to several hundred Kelvin above the decoupling point of the intergranular amorphous matrix phase. This observation, in conjunction with the q-dependence of the scattering, suggests the existence of long-range magnetic correlations between the iron particles through the paramagnetic matrix, in agreement with previous investigations. The characteristic wavelength of the dipole-field-induced spin disorder appears to be temperature independent. [less ▲]

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See detailEffect of magnetic field annealing on the soft magnetic properties of nanocrystalline materials
Ito, N.; Michels, Andreas UL; Kohlbrecher, J. et al

in Journal of Magnetism & Magnetic Materials (2007), 316(2), 458-461

The effects of static- and rotating-magnetic-field annealing on the magnetic softness and the magnetization alignments in nanocrystalline Fe84Nb6B10 have been investigated by means of DC magnetometry and ... [more ▼]

The effects of static- and rotating-magnetic-field annealing on the magnetic softness and the magnetization alignments in nanocrystalline Fe84Nb6B10 have been investigated by means of DC magnetometry and small-angle neutron scattering (SANS). At the remanent state, the SANS pattern obtained from the static-field annealed sample exhibited an enhanced SANS signal in the direction normal to the uniaxial anisotropy (Ku) field direction, indicating a well-developed long-range magnetization alignment along the direction of Ku. Contrarily, the SANS pattern for the rotating-field annealed sample is virtually isotropic at zero field, reflecting the lack of anisotropic magnetization alignments. The soft magnetic properties of nanocrystalline Fe84Nb6B10 are improved dramatically by rotating-field annealing due to the suppression of Ku. [less ▲]

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See detailA comparison of torque-strengths in micromagnetics
Michels, Andreas UL; Weissmüller, J.

in Journal of Magnetism & Magnetic Materials (2003), 258-259

In the approach-to-magnetic-saturation range, we present experimental data for the magnitude and applied magnetic-field dependence of the volume-averaged mean-square magnetostatic stray field |Hdb|^2 that ... [more ▼]

In the approach-to-magnetic-saturation range, we present experimental data for the magnitude and applied magnetic-field dependence of the volume-averaged mean-square magnetostatic stray field |Hdb|^2 that results from non-zero divergences of the magnetization from within the volume of bulk samples of nanocrystalline electrodeposited Ni and Co and coarse-grained polycrystalline cold-worked Ni. The magnitude of |Hdb|^2 is compared to the volume-averaged mean-square anisotropy field Hp|^2, which arises from the combined effect of magnetocrystalline and magnetoelastic anisotropy. [less ▲]

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