Role of higher-order effects in spin-misalignment small-angle neutron scattering of high-pressure torsion nickel

TL;DR

This study reveals that high-pressure torsion strain in nickel causes persistent spin misalignments detectable by small-angle neutron scattering, with higher-order effects playing a significant role in the observed scattering patterns.

Contribution

It demonstrates the importance of higher-order micromagnetic effects in interpreting SANS data for defect-rich strained nickel, extending beyond conventional theories.

Findings

Spin misalignments persist up to 4 T in HPT-strained Ni.

Observed anisotropy in scattering patterns cannot be explained by second or third order theories.

Higher-order effects are significant due to high defect density in strained nickel.

Abstract

Magnetic-field-dependent unpolarized small-angle neutron scattering (SANS) experiments demonstrate that high-pressure torsion (HPT) straining induces spin misalignments in pure Ni, which persist in magnetic fields up to 4 T. The spin-misalignment scattering patterns are elongated perpendicular to the applied magnetic field due to an unusual predominant longitudinal $sin^2(\theta)$-type angular anisotropy. Such a contribution cannot be explained by the conventional second order (in spin misalignment amplitude) micromagnetic SANS theory in the approach-to-saturation regime, nor can its magnitude relative to the other features of the cross sections by the third order micromagnetic SANS theory. This indicates that the high-density of crystal defects induced via HPT straining in Ni makes such higher-order effects in the micromagnetic SANS cross sections observable.