Magnetic small-angle neutron scattering on bulk metallic glasses

Doctoral thesis (2018)

The present PhD thesis is devoted to the exploration of the use of the magnetic small-angle neutron scattering (SANS) technique for analyzing the magnetic microstructure of bulk magnetic materials. More ... [more ▼]

The present PhD thesis is devoted to the exploration of the use of the magnetic small-angle neutron scattering (SANS) technique for analyzing the magnetic microstructure of bulk magnetic materials. More specifically, magnetic-field-dependent SANS has been utilized to study the magnetic microstructure of bulk metallic glasses (BMGs). The magnetic scattering is compared for soft magnetic and hard magnetic compositions in different mechanically treated states. On the basis of the continuum theory of micromagnetics, the correlation function of the spin-misalignment SANS cross section is computed and analyzed as a function of various external and material parameters. Analysis of the experimental correlation functions of the BMG reveals the existence of field-dependent anisotropic long-wavelength magnetization fluctuations on a scale of a few tens of nanometers. As a second aspect of this PhD work, we have explored the impact of the Dzyaloshinski-Moriya interaction on the elastic magnetic SANS cross section of microstructural-defect-rich materials. The effect was demonstrated by measuring polarized SANS on a nanocrystalline terbium sample and on a cold-rolled polycrystalline cobalt sample. [less ▲]

MAGNETIC SMALL-ANGLE NEUTRON SCATTERING ON BULK METALLIC GLASSES

Scientific Conference (2017, July 03)

Spin Structures of Textured and Isotropic Nd-Fe-B-Based Nanocomposites: Evidence for Correlated Crystallographic and Spin Textures

in Physical Review Applied (2017), 7

Magnetic small-angle neutron scattering on bulk metallic glasses

Scientific Conference (2016, March 08)

Bulk metallic glasses (BMG) are amorphous solids which are very well known for their excellent mechanical properties. In this contribution, we focus on their magnetic behavior and we discuss the influence ... [more ▼]

Bulk metallic glasses (BMG) are amorphous solids which are very well known for their excellent mechanical properties. In this contribution, we focus on their magnetic behavior and we discuss the influence of mechanical deformation on the magnetic microstructure as seen by magnetic-field-dependent small-angle neutron scattering (SANS). This technique allows one to investigate the spin distribution in the bulk of the material and on the nanometer length scale. We present and compare the results of unpolarized SANS on various BMG samples (as-cast, aged, deformed) and we analyze the SANS cross section in real space by computing the correlation function. [less ▲]

Magnetic SANS correlation functions of bulk magnetic materials

Poster (2015, September 02)

We present model calculations, based on the continuum theory of micromagnetics, for the correlation function of the spin-misalignment SANS cross section of bulk ferromagnets (e.g. elemental ... [more ▼]

We present model calculations, based on the continuum theory of micromagnetics, for the correlation function of the spin-misalignment SANS cross section of bulk ferromagnets (e.g. elemental polycrystalline ferromagnets, soft and hard magnetic nanocomposites, nanoporous ferromagnets, or magnetic steels). For such materials, the spin disorder which is related to spatial variations in the saturation magnetization and magnetic anisotropy field results in strong spin-misalignment scattering dΣM/dΩ along the forward direction [1]. When the applied magnetic field is perpendicular to the incoming neutron beam, the characteristics of dΣM/dΩ (e.g. the angular anisotropy on a two-dimensional detector or the asymptotic power-law exponent) are determined by the ratio of magnetic anisotropy-field strength Hp to the jump ΔM in the saturation magnetization at internal interfaces. Here, we analyze the corresponding one and two-dimensional real-space correlations as a function of applied magnetic field, ratio Hp/ΔM, single-particle form factor, and particle volume fraction. Finally, we compare the theoretical results for the correlation function to experimental data on a Nd-Fe-B-based nanocomposite. [less ▲]

Field-Induced Spin Helix Chirality in Nanocrystalline Ho

Poster (2014, November)