Significant enhancement in the saturation magnetization M_(s) and coercivity H_(c) of yttrium iron garnet (YIG) films has been obtained by a simple method of surface infiltration of CoO. Deposition of a CoO overlayer under specific conditions by a low-pressure chemical-vapor deposition process over the crystallized YIG film has been observed to show high out-of-plane H_(c) and M_(s) values of 282.7 and 85.7 kA/m, respectively. The effect of the CoO deposition rate, temperature dependence of coercivity H_(c), and annealing studies have been described that indicate CoO infiltration during the growth, resulting in a Co-rich YIG layer, and generation of interfacial stress are responsible for this unusual effect. Delineation of the interface by ion-beam etching in conjunction with magnetic studies has led to the understanding of the nature of the Co-rich YIG interfacial layer. Enhanced H_(c) and M_(s) values without the usual method of Ce~(4+) compensation of Co-doped YIG films described in this letter are of considerable use for application in high-density magneto-optic recording media.
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