We provide the experimental research on a novel type of all-dielectric magnetic structure designed to achieve an enhanced magneto-optical response. 1D grating fabricated via etching of bismuth substituted iron garnet film supports the excitation of optical guided modes, which are highly sensitive to the external magnetic field. A unique feature of proposed structure is the synergetic combination of high transparency, tunability, high Q-factor of the resonances and superior magneto-optical response that is two orders higher in magnitude than in the non-structured smooth iron-garnet film. The considered all-dielectric magnetic garnet structures have great potential in various fields including the magneto-optical modulation of light, biosensing and magnetometry.