How does replacing yttrium with gadolinium change the magnetism of a garnet ferrite?

In garnet ferrites, such as yttrium iron garnet (YIG) with the formula ${\text{Y}}_3{\text{Fe}}_5{\text{O}}_{12}$, the net ferrimagnetism arises from the complex antiparallel alignment of magnetic moments among three types of lattice sites: tetrahedral, octahedral, and dodecahedral. In pure yttrium iron garnet, the yttrium ions are not magnetic, meaning the net magnetic moment is determined solely by the iron ions.12

When a rare-earth ion such as gadolinium (Gd) is substituted for yttrium, the magnetism of the material changes because the gadolinium ion itself contributes to the ferrimagnetism. This substitution introduces an additional magnetic component into the crystal structure, which interacts with the existing magnetic moments of the iron ions, thereby altering the overall magnetic properties of the garnet.21