Embodiments disclosed herein include methods of modifying synthetic garnets used in RF applications to reduce or eliminate Yttrium or other rare earth metals in the garnets without adversely affecting the magnetic properties of the material. Some embodiments include substituting Bismuth for some of the Yttrium on the dodecahedral sites and introducing one or more high valency ions to the octahedral and tetrahedral sites. Calcium may also be added to the dodecahedral sites for valency compensation induced by the high valency ions, which could effectively displace all or most of the Yttrium (Y) in microwave device garnets. The modified synthetic garnets with substituted Yttrium (Y) can be used in various microwave magnetic devices such as circulators, isolators and resonators.