Preparation of Bi-Substituted YIG Garnets by Sol-Gel Synthesis and Their Magnetic Properties

Bi, Al-substituted YIG was synthesized by the sol-gel method using a solution of yttrium, iron, bismuth and aluminum nitrates dissolved in ethylene glycol. Films were fabricated by spin-coating a gel solution onto glass substrate. The film thickness was controlled by repeating the spin-coating several times. Coated films were subjected to heat treatment in air at 700°C for 4 hours to obtain YIG crystal. The magnetization of Bi
x
Y
3-x
Fe
5
O
12
lies in the plane of the film. Films magnetized normal to the film plane were obtained at a composition of Y
1.5
Bi
1.5
Fe
3.8
A1
1.2
O
12
, but the magnetization tends to incline toward the film plane with increasing film thickness. This may be explained in terms of the stress due to substrate constraint: stress relief becomes significant as the film thickness is increased by repeated spin-coating. This can, to a great extent, be eliminated by heat treatment after each spin coating. The magneto-optical Faraday rotation in films is compared for films annealed after the completion of spin-coatings, and films annealed after each spin-coating.