To the best of our knowledge, rare earth doped yttrium iron garnet is still the main material used for magneto-optical devices. They include bismuth doped YIG, bismuth, terbium doped YIG and cerium doped YIG. Other materials such as Wely semimatels are still under theoretical study[1]. We have added comments to these materials in the manuscript. Revisions: Page 1, line 21, added “At present, rare earth doped yttrium iron garnet (RIG) is the most widely used magneto-optical material in integrated MO devices.” Point 2:
It is not indicated in the introduction whether any alternative to thin films of yttrium iron garnet is currently being considered for use as magneto-optical resonators.