This study investigates the effects of incorporating ¹¹B₄C interlayers into Fe/Si multilayers, with a focus on interface quality, reflectivity, polarization, and magnetic properties for polarizing neutron optics. It is found that the introduction of 1–2 Å ¹¹B₄C interlayers significantly improves the interface sharpness, reducing interface width and preventing excessive Si diffusion into the Fe layers. X-ray reflectivity and polarized neutron reflectivity measurements show enhanced reflectivity and polarization, with a notable increase in polarization for 30 Å period multilayers. The inclusion of interlayers also helps prevent the formation of iron-silicides, improving both the magnetic properties and neutron optical performance. However, the impact of interlayers is less pronounced in thicker-period multilayers (100 Å), primarily due to the ratio between layer and interface widths. These results suggest that ¹¹B₄C interlayers offer a promising route for optimizing Fe/Si multilayer performance in polarizing neutron mirrors.