This study further investigates the effects of ¹¹B₄C co-sputtering on the structural and optical properties of Fe/Si stacked multilayers, with a focus on neutron supermirror applications. X-ray and neutron reflectivity techniques confirm with greater clarity that ¹¹B₄C incorporation improves interface sharpness, reduces roughness, and enhances reflectivity for various multilayer periods, compared to earlier studies on a single period thickness. Neutron reflectivity measurements show reduced spin-flip intensities, while wafer-curvature measurements indicate a 50 % reduction in internal stress, allowing for higher mechanical stability of the multilayers. These improvements are attributed to the amorphization of Fe layers, which also suppress the formation of structural and magnetic domains responsible for stress and spin-flip scattering. In contrast, the pure Fe/Si sample exhibits a persistent half-order Bragg peak, indicating residual antiferromagnetic coupling. The results demonstrate that ¹¹B₄C enhances neutron optics by reducing spin-flip effects, increasing reflectivity and polarization, and alleviating stress, enabling the use of polarizers at reduced external fields compared to pure Fe/Si multilayers. These findings establish ¹¹B₄C as a transformative material for advancing neutron supermirror technology, paving the way for more efficient, stable, and high-performance polarizers in next-generation neutron optics.