Crystallization of yttrium-iron garnet (YIG) in thin films: Nucleation and growth aspects
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Crystallization of yttrium-iron garnet (YIG) in thin films: Nucleation and growth aspects Michael V Zaezjev1, Manda Chandra Sekhar1, Marcello Ferrera1, Luca Razzari1, Barry M Holmes2, Marc Sorel2, David C Hutchings2, Alain Pignolet1, and Roberto Morandotti1 1 INRS-EMT, Varennes, J3X 1S2, Canada 2 University of Glasgow, Glasgow, United Kingdom ABSTRACT We have studied the crystallization of the yttrium - iron garnet (Y3Fe5O12, YIG) polycrystalline phase in thin films fabricated by means of pulsed laser deposition. Films were deposited on MgO substrates in vacuum, in argon, and in oxygen. A subsequent post-deposition heat treatment (annealing) was done at 800°C in air. We have shown that the crystallization of YIG was precluded by co-existent parasitic phases present in the as-deposited films. Specifically, the growth of the parasitic phase needs to be suppressed in order to get a single-phase polycrystalline YIG. Lowering the substrate temperature has been shown to be a simple and effective way to suppress the growth of parasitic phase and to obtain good quality YIG films after thermal treatment. This procedure has been demonstrated to be successful even when the YIG films were grown in vacuum and their composition was significantly out of stoichiometry. INTRODUCTION Rare-earth iron garnets (X3Fe5O12), X being a rare earth, have demonstrated unique magnetooptic (MO) properties making them the materials of choice for a variety of devices and applications such as optical isolators, magnetic field sensors, and magnetic flux visualizators. In particular, the one-chip integration of optical isolators with III-V semiconductor laser diodes has remained an extremely challenging tasks, yet necessary in order to reduce costs and improve compactness. While some promising solutions have been developed for the general design of such devices [1, 2], they all require the presence of a high-quality thin MO layer on top of the III-V quantum well structure. One of the most challenging tasks is to develop the capability of achieving a high Faraday rotation (FR) in a thin and short magnetooptic section. This issue may only be addressed by means of a good quality MO material having a crystal structure associated with a high Faraday rotation, such as garnets (see, for ex. [3]). Throughout the last decades, several techniques have demonstrated the potential to create good quality MO garnet thin films on different substrates, but some technological aspects of these processes have remained unclear. The positive results reported so far have been mostly obtained by trial and error procedures without an in depth understanding of how the numerous variable parameters affect the final structure. For example, it is commonly thought that oxygen is required in the deposition atmosphere to get fully oxidized YIG films. At the same time it is not yet clear how critical the stoichiometry really is for the crystallization of YIG thin films. In this paper we systematically study the crystallization of the yttrium-iron garnet (YIG, or Y3Fe5O12
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