Increased neutron reflectivity and polarization of neutron-optical engineered Fe/11B4CTi multilayer optics

The concept of scattering length density tuning for improved polarization is investigated for Fe/11B4⁢CTi multilayers and compared to the commonly used Fe/Si system in polarizing multilayer neutron optics. X-ray and neutron reflectivity, magnetization, and neutron polarization were measured on such multilayers, highlighting differences from conventional Fe/Si multilayers. The multilayer systems were deposited with 25 Å period thickness, a layer thickness ratio of 0.35, and 20 periods using ion-assisted dc magnetron sputtering. Replacing Si with 11B4⁢CTi for these multilayers showed an increase in reflectivity due to a reduction in interface width. Tuning the ratio between 11B4⁢C and Ti in the nonmagnetic layers enabled a wide range of scattering length density contrasting and matching for spin-down neutrons, which in turn led to an improved polarization. These findings demonstrate the potential of Fe/11B4⁢CTi multilayers as a promising option for polarizing neutron optics and highlight the concept of scattering length density tuning in a large range using 11B4⁢CTi.