Enhanced Polarizing Neutron Optics with 11B4C Incorporation : SLD Tunability, Interface Refinement, and Elimination of Magnetic Coercivity

Abstract: This thesis explores novel strategies for improving Fe-based polarizing neutron optics, a critical part for improving neutron scattering methods to study materials science, physics, biology, medicine, chemistry and cultural heritage. Polarization analysis is important in uncovering data on magnetic domains, protein structures, molecular composition and orientation in biological systems, and ion-diffusion mechanisms that would otherwise be inaccessible. However, conventional methods, particularly state-of-the-art multilayer polarizing neutron optics, are hindered by low specular reflectivity, low polarization at higher scattering vectors/angles, high diffuse scattering and the need for high external magnetic fields for polarizer magnetization.  The outcomes leading to this thesis, introduces the concept of scattering length density tuning, strategies to decrease the interface width, the diminishing of lateral correlation and magnetic coercivity. All improvements realized by introducing 11B4C in clever ways.The multilayers were deposited using ion-assisted DC magnetron sputter deposition (DCMS). Our improvement of Fe-based multilayer mirrors all revolves around the use of 11B4C. 11B4C in various concentrations can be used together with other materials to tune the scattering length density contrasts. It can amorphize the interfaces and layers to achieve smaller interface width, diminish lateral correlations and eliminate magnetic coercivity. In other words, increase reflectivity, increase polarization, decrease diffuse scattering and saturate at lower fields.   The multilayers were mainly characterized using X-ray reflectivity (XRR), X-ray diffraction (XRD), grazing incidence small/wide angle X-ray scattering (GISAXS/GIWAXS), elastic recoil detection analysis (ERDA), magneto-optical Kerr effect (MOKE), vibrating sample magnetometry (VSM), transmission electron microscopy (TEM) and polarized neutron reflectivity (PNR).  All results prove the benefit of using 11B4C in Fe-based polarizing neutron optics.