Formation and Magnetic Properties of Uitrahigh Density Fe_3Si Nanodots Epitaxially Grown on Si(111) Substrates Covered with Ultrathin SiO_2 Films

摘要

The epitaxial growth technique of uitrahigh density (>10~(12)cm~(-2)) Fe_3Si nanodots (NDs) on Si(111) substrates was developed using an ultrathin SiO_2 film technique. Low temperature (<300 ℃) growth of the Fe_3Si NDs was needed to suppress the interdiffusion between Fe atoms deposited on the sample surface and Si atoms in the substrate. The ND shape changed drastically from sphere to discontinuous films as the Fe content was increased slightly from a stoichiometric ratio of Fe: Si of 3:1. For almost-spherical NDs with the uitrahigh density, a transition from superparamagnetism to ferromagnetism was observed at specific temperatures, the ferromagnetism of which included the magnetic dipole interactions in uitrahigh density ND system. These ND structures with ND size dependence of the coercive force were expected to be selectively used as both magnetically fixed and free layers in magnetic tunneling junction structures only by changing the ND size.