Magnetic iron garnets (A3Fe5O12, A = Y, Bi, Tm, or A3 = Bi0.8Y2.2, Ce1Y2) are ferromagnetic insulating oxides with multiple useful properties including very low magnetic Gilbert damping and extremely low coercivity in Y3Fe5O12 (YIG), perpendicular magnetic anisotropy in Tm3Fe5O12 and strong magneto-optical response (Kerr and Faraday rotation) in the visible and near-infrared regions when A site is substitutionally-doped with Cerium or Bismuth. These unique functional properties of these oxides enable testing novel physical phenomena such as inverse spin Hall effect, spin-Seebeck effect and proximity-induced magnetism in topological insulators as well as cutting-edge device applications for ultra-low energy non-volatile switching memory or magnon processing chips.
We have established growth procedures for high-quality epitaxial magnetic garnet thin films on Gd3Ga5O12 (GGG) substrates using pulsed laser deposition with bulk-like magnetic properties for films with thicknesses between 6-400 nm. Damping (α) of YIG films grown on GGG substrates are consistently in the low 10-4 range and coercivity < 2 Oe for films with thicknesses 17-360 nm. Currently, our group is working on using garnet films to help develop magnonic crystal cavity resonators, on-chip control and readout of the individual spins in nitrogen vacancy centers assisted by magnons propagating in YIG, thermomagnonic power generation and spin-Seebeck cooling of electronic chips and novel room-temperature low-energy and non-volatile switching mechanisms. CeYIG films are useful for their magnetooptical properties, and we have measured the Faraday rotation of CeYIG and BiYIG films for optical applications.
To integrate garnets into electronic devices, growth on non-garnet substrates is essential. We have developed processes to fabricate polycrystalline garnet films on silica, nitride and quartz, with properties such as magnetization comparable to single crystal garnets. CeYIG is particularly interesting for magnetooptical devices such as integrated isolators.