High-resolution x-ray-diffraction analysis of epitaxially grown yttrium iron garnet films on gadolinium gallium garnet

Abstract

X-ray-diffraction analysis was applied to determine the lattice strain and degree of crystalline perfection of yttrium iron garnet (YIG) films on [100]- and [111]-oriented gadolinium gallium garnet (GGG) substrates. Rocking curves were measured with a high-resolution x-ray diffractometer in which a four-reflection monochromator in a (+,−,−,+) setting produces a beam with a very small angular divergence (2.3 μrad, Mo Kα1) and energy bandwidth (about 80 meV). Therefore a series of different reflections of intrinsic angular width could be obtained from the same crystalline layer system. The dynamical diffraction theory was used to compute the rocking curves. A simple recursion formula allowed a computer simulation of the measured reflectivity. The fit to the measured rocking curves for each reflection resulted in the probable change of the lattice constant with depth. It was possible to successfully fit the rocking curves of four different reflections of one YIG/GGG crystal with only one strain profile. The changing of the lattice constant gives an insight into the crystal growth and could be important for improving the process.