Hologram memory is a strong candidate for optical storage due to its high recording density and high data transfer rate. We have studied and engineered a magnetic hologram memory medium using a stable magnetic garnet as recording material. To record a deep and clear magnetic hologram, it is important to control the heat diffusion generated during recording. Numerical simulation suggested that a multilayer structure with transparent heat-dissipation layers would be effective to address this. We fabricated a multilayer magnetic medium for a collinear magnetic hologram. This medium exhibited a diffraction efficiency as high as that of the single layered one, and errorless recording and reconstruction was achieved with the magnetic assist technique.