Optimizing the quality of epitaxial Y3Fe5O12 thin films via a two-step post-annealing process

Background: Yttrium iron garnet (Y3Fe5O12, YIG) is a prototype magnetic garnet, which possesses the lowest magnetic damping (α) value so far on the earth among all discovered or synthesized materials. This makes it the best candidate for categories of next generation spintronic devices, possessing great application potentials. Methods: A two-step annealing method, with first annealing carried out at a relative low temperature and second annealing at a relatively higher temperature, had been used for the first time to crystallize room temperature sputtered amorphous Y3Fe5O12 (YIG) films on Gd3Ga5O12 (GGG) substrates. The crystalline structure, surface morphology, static and dynamic magnetic properties of the obtained YIG films were characterized through X-ray diffraction (XRD), atomic force microscopy (AFM), vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) systems, respectively. Results: It was found that the YIG films obtained via this elaborate annealing method, have a much smoother surface, lower coercivity field, and better dynamic magnetic properties, than that of the YIG films annealed by ordinary one-step approach. Particularly, the ferromagnetic resonance (FMR) linewidth of the best two-step annealed 25 nm YIG film is lower than ~7 Oe at frequency of 10 GHz. Conclusions: Our work clarifies that this two-step annealing approach can effectively improve the quality of the obtained epitaxial YIG films on GGG substrates.