Thomas Gage1 Bethanie Stadler1 David Flannigan1

1, University of Minnesota, Minneapolis, Minnesota, United States

Yttrium iron garnet (YIG) has a range of applications in the fields of spintronics and magneto-optics due to its low damping constant and Faraday rotation. Utilizing thin YIG films, these properties can be taken advantage of in nanoscale devices, but attempts to do so have necessitated the usage of lattice matched substrates, such as gallium gadolinium garnet, limiting practical applications. Recent advances towards incorporating YIG into silicon based devices have been promising, showing that YIG can be grown on silicon with reasonably high quality by sputtering and annealing. These studies have rarely examined crystallization mechanisms or studied any fundamental crystallization behavior. Here we report an in situ TEM study of the crystallization behavior of YIG on SiO2, specifically looking at fundamental crystallization properties and mechanisms.
Thin amorphous YIG films (20-100 nm) were deposited on SiO2 TEM windows by RF sputtering. These YIG films were then crystallized in situ by a laser in the TEM column. The crystallization phenomenon was observed in bright-field as well as diffraction mode TEM. Bright-field TEM allows for studying nucleation rate, crystallization front velocity as well as crystallization geometries. Diffraction TEM allows for studying phase formation, percent crystallinity, instantaneous temperature, as well as texturing. Results from time resolved diffraction patterns show Avrami crystallization behavior of a highly textured nanocrystalline phase which forms prior to the YIG phase. The YIG phase also displays an Avrami growth behavior. These phases formed with Avrami constants (n) of 2 and 1 respectively at temperatures commonly used in annealing (800-1000°C). By continuing to study this behavior, we can optimize the temperature profile for higher quality YIG films on non-garnet substrates.
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