Spin-disorder-induced angular anisotropy in polarized magnetic neutron scattering

TL;DR

This paper reports the discovery of a new angular anisotropy in polarized neutron scattering caused by spin disorder in inhomogeneous magnetic materials, supported by experimental data and micromagnetic theory.

Contribution

It introduces the first experimental observation of spin-disorder-induced anisotropy in polarized SANS and links it to material inhomogeneity and exchange stiffness measurement.

Findings

Observed anisotropy in polarized SANS cross section.

Demonstrated method to determine exchange-stiffness constant.

Revealed relevance to nuclear-magnetic interference in neutron scattering.

Abstract

We experimentally report a hitherto unseen angular anisotropy in the polarized small-angle neutron scattering (SANS) cross section of a magnetically strongly inhomogeneous material. Based on an analytical prediction using micromagnetic theory, the difference between the spin-up and spin-down SANS cross sections is expected to show a spin-disorder-induced anisotropy. The effect is particularly pronounced in inhomogeneous magnetic materials, such as nanoporous ferromagnets, magnetic nanocomposites, or steels, which exhibit large nanoscale jumps in the saturation magnetization at internal pore-matrix or particle-matrix interfaces. Analysis of the experimental neutron data constitutes a method for determining the exchange-stiffness constant. Our results are generic to the nuclear-magnetic interference terms contained in the polarized magnetic neutron scattering cross section and might also be of relevance to other neutron techniques.