We utilized a metal propionate solution to prepare polycrystalline bismuth-substituted yttrium iron garnets through the metal-organic decomposition process. After conducting thorough optimization, we successfully synthesized a garnet that exhibited a high magneto-optic response directly at the end of an optical fiber. A notable achievement of our work lies in the ability to restrict the size and position of the garnet to match the dimensions of the fiber's core. The functionalized fiber was integrated into a magneto-optical sensor setup, offering the flexibility to operate either in the Faraday rotation or magnetic circular dichroism mode.