| A CoxFe100− x metal/native oxide multilayer (MNOM) structure has been developed and characterized. The MNOM consists of thin (∼20 Å) nanocrystalline layers of a high-moment CoxFe100− x alloy that have been exposed in situ to oxygen to form metal/native oxide bilayers. Over a wide range of alloy composition (0 < x < 90), the MNOM exhibits a large saturation magnetization, a low-dispersion uniaxial magnetic anisotropy, and a low coercivity. These properties lend the MNOM to applications demanding high permeability at ultra high-frequency. The native oxide, which is magnetic for x < 90, plays an important role in establishing these technologically-significant properties.; The predominantly interfacial ∼13 Å buried native Fe oxide orders well above room temperature, with a volume-averaged magnetization exceeding that of Fe3O4 by ∼40% and of γ-Fe2O 3 by ∼90%. The native oxide consists of two magnetic components, distinguished by the temperature dependence and ordering of their respective ionic spins. The minority component, amounting to 30% of the oxide, has no net moment and a strongly temperature-dependent ionic moment, while the majority component has a net moment with a magnitude and temperature dependence comparable to those of metallic Fe. These two components are shown to represent two distinct ionic sites in a single, previously unidentified “in-terfacial” Fe oxide phase. The oxide is found to have the stoichiometry of FeO which, in the bulk is an antiferromagnet which orders below 197 K. The contrasting magnetism of the buried native Fe oxide is stabilized in part by the proximate Fe metal. Similar magnetic properties are observed in the buried Co xFe100−x native oxides with x < 90. Ferromagnetic exchange coupling between the metal and native oxide in the MNOM is explicitly demonstrated. |
