Micromagnetic structures of nanocrystalline ferromagnetic materials – comparison of simulation and experiment

Abstract

The micromagnetic structure of nanocrystalline ferromagnetic materials is characterized by local fluctuations induced by the randomly varying magnetocrystalline anisotropy of the individual grains. Micromagnetic simulations may improve the understanding of the relevant features and the interpretation of the experimental observations of the magnetic structure. In this study we investigate the magnetic structure of nanocrystalline FeSi and Co model systems with average grain sizes of 20 nm to 60 nm. Small angle neutron scattering (SANS) is a suitable technique to study the micromagnetic structures of nanocrystalline materials at the nanometer scale. The simulated SANS curves for the FeSi model systems are compared with the experimental SANS curves of Vitroperm samples. It is found that the scattering at high fields is dominated by the local anisotropy fluctuations which can be well reproduced by the simulations. The simulations of the nanocrystalline hcp Co show that the stray fields resulting from the local magnetic fluctuations should lead to an observable contrast in magnetic force microscopy (MFM) images. We show that the contrast observed in the real MFM images of thin nanocrystalline hcp Co films compares well with the simulated image contrast with respect to magnitude and length scale of the observed fluctuations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic small-angle neutron scattering

“…In this section we review a novel micromagnetic simulation methodology which takes site-dependent magnetic parameters (saturation magnetization, magnetic anisotropy) and interactions (exchange and magnetodipolar field) into account. This approach enables studies of the magnetic microstructure of a wide range of polycrystalline magnetic materials such as singlephase nanocrystalline magnets, magnetic nanocomposites, recording media, or magnetic particles in a nonmagnetic matrix (Erokhin et al, 2012a(Erokhin et al, ,b, 2015Löffler et al, 2005;Michels et al, 2014;Ogrin et al, 2006;Saranu et al, 2008;Zighem et al, 2013).…”

Polarization-analyzed small-angle neutron scattering. II. Mathematical angular analysis

“…solvated magnetic nanoparticles that form chains in response to application of a magnetic field or shearing force). Two approaches have been adopted to analyze PASANS data: (1) to reproduce the combined structural and magnetic scattering patterns from micromagnetic models (Lö ffler et al, 2005;Ogrin et al, 2006;Michels & Weissmü ller, 2008;Saranu et al, 2008) and (2) to separate the structural from the magnetic scattering in terms of the three mutually orthogonal magnetic scattering contributions (Schä rpf & Capellmann, 1993;. Both approaches have their merits and may be highly complementary.…”

Magnetostriction and Magnetic Heterogeneities in Iron-Gallium

“…Four lobes with 90 spacing in can be explained by a dipolar magnetic field surrounding the heterogeneity core [24]. Developing numerical methods such as micromagnetic simulation augur well for unraveling further details [25], and will be addressed in future work. We also observe four lobes at intermediate magnetic fields %10 mT, but these data are not shown here.…”