Application of a Portable $^3$He-Based Polarization Insert at a Time-of-Flight Neutron Reflectometer

TL;DR

This paper demonstrates the use of a portable 3He-spin filter as a broadband polarizer for a Time-of-Flight neutron reflectometer, introducing a simple characterization method and data analysis procedure for weak magnetic signals.

Contribution

It introduces a transportable 3He-spin filter for neutron reflectometry and a novel two-wavelength method for its characterization, enabling effective magnetic signal detection.

Findings

Successful demonstration of a portable 3He-spin filter in neutron reflectometry.

Effective extraction of weak magnetic signals from reflectivity data.

Validation of the method on magnetic heterostructures with external magnetic fields.

Abstract

The suitability of a transportable 3He-spin filter as temporary broadband polarizer for a Time-of-Flight neutron reflectometer is demonstrated. A simple two-wavelength method for characterisation of a 3He-spin filter is proposed, which can be applied even if the absolute transmittance of the 3He-spin filter cannot be accurately determined. We demonstrate the data treatment procedure for extracting the spin-up and spin-down neutron reflectivity from measurements obtained with a time dependent 3He polarization. The extraction of a very weak magnetic signal from reflectivity data, measured on the in-situ grown magnetic heterostructure Fe1 nm/Cu20 nm/Sisubstrate in an externally applied magnetic field of 30mT is presented and compared to similar measurements on the growth stage Cu20 nm/Sisubstrate of the very same sample, which does not yet contain any magnetic material.