Measurement and modeling of polarized specular neutron reflectivity in large magnetic fields

TL;DR

This paper develops a theoretical framework and experimental guidelines for polarized neutron reflectometry in large magnetic fields, accounting for spin state degeneracy removal and non-collinear magnetization effects.

Contribution

It introduces a comprehensive model for polarized neutron reflectivity in strong magnetic fields, including the impact of non-collinear magnetization on spin-flip scattering.

Findings

The theory accurately predicts scattering behavior in large magnetic fields.

Experimental practices are recommended for precise measurements.

An example measurement demonstrates the model's applicability.

Abstract

The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin-up and spin-down neutrons. For polarized neutron reflectometry, this must be included in the reference potential energy of the Schr\"odinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin-flip scattering) and so this additional potential is constant throughout the scattering region. When there is non-collinear magnetization in the sample however, there will be significant scattering from one spin state into the other and the reference potentials will differ between the incoming and outgoing wavefunctions, changing the angle and intensities of the scattering. The theory of the scattering and recommended experimental practices for this type of measurement are presented, as well as an example measurement.