Stress-induced magnetic properties of PLD-grown high-quality ultrathin YIG films

Abstract

Yttrium iron garnet (YIG:Y3Fe5O12) thin films were grown on (111) gadolinium gallium garnet (Gd3Ga5O12, GGG) substrates using pulsed-laser deposition under several different deposition and annealing conditions. X-ray diffraction measurements revealed that the crystallographical orientation of the YIG films is pseudomorphic to and the same as that of the GGG substrate, with a slight rhombohedral distortion along the surface normal. Furthermore, X-ray reciprocal space mapping evidenced that in-situ annealed YIG films during film growth are under compressive strain, whereas ex-situ annealed films have two different regions under compressive and tensile strain. The saturation magnetization (4πMS) of the films was found to vary, according to the deposition conditions, within the range of 1350 to 1740 G, with a very low coercivity of HC < 5 Oe. From ferromagnetic resonance (FMR) measurements, we estimated the effective saturation magnetization (4πMeff) to be 1810 to 2530 G, which are larger than that of single crystalline bulk YIG (∼1750 G). Such high values of 4πMeff are attributable to the negative anisotropy field (HU) that increases in size with increasing compressive in-plane strain induced in YIG films. The damping constant (αG) of the grown YIG films was found to be quite sensitive to the strain employed. The lowest value of αG obtained was 2.8 × 10−4 for the case of negligible strain. These results suggest a means of tailoring HU and αG in the grown YIG films by the engineering of strain for applications in spintronics and magneto-optical devices.