Uniaxial polarization analysis of bulk ferromagnets: theory and first experimental results1

• Published in: Journal of applied crystallography 2022-05, Vol.55 (Pt 3), p.569-585
• Main Authors: Malyeyev, Artem, Titov, Ivan, Dewhurst, Charles, Suzuki, Kiyonori, Honecker, Dirk, Michels, Andreas
• Format: Article
• Language: English
• Subjects: Research Papers
• ISSN: 0021-8898; 1600-5767
• DOI: 10.1107/S1600576722003508

Based on the continuum theory of micromagnetics, theoretical expressions for the polarization of the scattered neutron beam in uniaxial small-angle neutron scattering have been derived and their predictions tested by analyzing experimental data on a soft magnetic nanocrystalline alloy. The here-presented theoretical framework forms the basis for polarized real-space methods such as spin-echo small-angle neutron scattering, spin-echo modulated small-angle neutron scattering and polarized neutron dark-field contrast imaging. On the basis of Brown’s static equations of micromagnetics, the uniaxial polarization of the scattered neutron beam of a bulk magnetic material is computed. The approach considers a Hamiltonian that takes into account the isotropic exchange interaction, the antisymmetric Dzyaloshinskii–Moriya interaction, magnetic anisotropy, the dipole–dipole interaction and the effect of an applied magnetic field. In the high-field limit, the solutions for the magnetization Fourier components are used to obtain closed-form results for the spin-polarized small-angle neutron scattering (SANS) cross sections and the ensuing polarization. The theoretical expressions are compared with experimental data on a soft magnetic nanocrystalline alloy. The micromagnetic SANS theory provides a general framework for polarized real-space neutron methods, and it may open up a new avenue for magnetic neutron data analysis on magnetic microstructures.