A synthetic garnet material comprising a structure represented by the formula Y3-x-2y−zBixCa2y+zFe5-y-z-aVyZrzAlaO12, bismuth occupying x formula units of dodecahedral sites, zirconium occupying z formula units of octahedral sites, vanadium occupying y formula units of tetrahedral sites, calcium occupying 2y+z formula units of the dodecahedral sites to compensate for a valency imbalance resulting from the presence of zirconium and vanadium, aluminum occupying a formula units of the tetrahedral sites while having the octahedral sites substantially free of aluminum, the quantity a being greater than zero, such that saturation magnetization of the material decreases in a substantially linear manner as the quantity a increases to an upper limit value of at least 0.6.