Effects of post-deposition annealing on the structure and magnetization of PLD grown Yttrium Iron Garnet films

Abstract

We report on the recrystallization of 200 nm thick as-grown Yttrium Iron Garnet (Y_3.4 Fe_4.6 O_12) films on (111) face of Gadolinium Gallium Garnet (GGG) single crystals by post-deposition annealing. Epitaxial conversion of the as-grown microcrystalline YIG films was seen after annealing at 800oC for more than 30 minutes both in ambient oxygen as well as in air. The as-grown oxygen annealed samples at 800oC for 60 minutes crystallize epitaxially and show excellent figure-of-merit for saturation magnetization (MS = 3.3 {\mu}B/f.u., comparable to bulk value) and coercivity (HC ~ 1.1 Oe). The ambient air annealing at 800oC with a very slow rate of cooling (2oC/min) results in a double layer structure with a thicker unstrained epitaxial top layer having the MS and HC of 2.9 {\mu}B/f.u. and 0.12 Oe respectively. The symmetric and asymmetric Reciprocal space maps of both the samples reveal a locking of the in-plane lattice of the film to the in-plane lattice of substrate, indicating a pseudomorphic growth. The residual stress calculated by sin^2 {\psi} technique is compressive in nature. The lower layer in air annealed sample is highly strained, whereas, the top layer has negligible compressive stress.