Magnetic properties of yttrium iron garnet thin films changed through surface modification by CoO overlayer growth for magneto-optic recording applications

Abstract

Significant changes in the saturation magnetization, M s and coercivity, H c of yttrium iron garnet (YIG) thin films have been achieved through surface modification by an overlayer growth of CoO. Low pressure chemical vapor deposition of a CoO overlayer over extended (∼45 min) time at slow (∼10 nm/min) rate over a crystallized YIG film resulted in out of plane H c and M s values of 282.7 and 85.7 kA/m, respectively. For an unmodified YIG film corresponding M s and H c values are much smaller at 7.5 and 21.3 kA/m, respectively. Study of critical effects of CoO thickness and deposition rate, thermal diffusion of CoO and temperature dependence of coercivity have been described which indicate formation of a Co-rich YIG interface layer during low pressure chemical vapor deposition (LPCVD) growth though interaction between CoO and YIG and generation of interfacial stress are responsible for this unusual changes in the magnetic properties. Magnetization studies of CoO/YIG bilayer structures after sequential etching of surface and interface regions by energetic Ar + ion beam suggest that Co-rich YIG interface layer is caused by Co 2+ infiltration into YIG surface. Realization of high M s and H c values in bilayer CoO/YIG films without uniform doping of YIG by Co 2+ and inclusion of tetravalent non-magnetic compensating Ce 4+ or Ge 4+ ions as described in this paper are attractive for application as high-density magneto-optic recording media.