Spin-resolved off-specular neutron scattering from magnetic domain walls using the polarized $^3He$ gas spin filter

TL;DR

This study demonstrates the use of polarized helium-3 gas filters and neutron resonant enhancement to measure spin-polarized diffuse neutron scattering from magnetic domains in an exchange-biased bilayer, revealing asymmetric and resonance-dependent scattering features.

Contribution

It introduces a novel application of polarized helium-3 gas filters combined with neutron resonant enhancement to analyze magnetic domain structures via off-specular neutron scattering.

Findings

Strong diffuse spin-flip scattering observed at resonance conditions.

Asymmetry in off-specular scattering intensities for different spin states.

Resonance position splitting correlates with stray magnetic fields.

Abstract

We report on the use of the polarized $^3$He gas filter and neutron resonant enhancement techniques for the measurement of spin-polarized diffuse neutron scattering due to ferromagnetic domains. A CoO/Co exchange biased bilayer was grown on a Ti/Cu/$Al_2O_3$ neutron resonator template. The system is cooled in an applied magnetic field of $H_a=2000$ Oe through the N\'{e}el temperature of the antiferromagnet to 10 K where the applied magnetic field is swept as to measure the magnetic hysteresis loop. After the second magnetization reversal at the coercive field $H_{c2}=+ 230$ Oe, the system is supposed to approach the original magnetic configuration. In order to prove that this is not the case for our exchange biased bilayer, we have measured four off-specular maps I++, I+-, I-+, I-- at $H_a \approx + 370$ Oe, where the Co magnetic spins were mostly reversed. They show a striking behavior in the total reflection region: while the nonspin-flip scattering exhibits no diffuse reflectivity, the spin-flip scattering shows strong diffuse scattering at incident angles which satisfy the resonance conditions. Moreover the spin-flip off-specular part of the reflectivity is asymmetric. The I-+ intensity occurs at higher exit angles than the specularly reflected neutrons, and the I+- intensity is shifted to lower angles. Their intensities are noticeably different and there is a splitting of the resonance positions for the up and down neutron spins ($\alpha_{n} ^{+} \ne \alpha_{n} ^{-}$) . Additionally, a strong influence of the stray fields from magnetic domains to the resonance splitting is observed.