Current-perpendicular spin valves with partially oxidized magnetic layers for ultrahigh-density magnetic recording

Magnetoresistance (MR) of current-perpendicular spin valves with nano-oxide layers (NOLs) has been investigated. Insertion of a NOL in a spacer between free and pinned magnetic layers can increase both resistance and MR ratio of the spin valves to the level that satisfies the needs for over 150-Gb/in² recording density. It is shown that the MR enhancement is strongly NOL-material dependent; ferromagnetic CoFe(B) alloys are found to be quite effective in the improvement, while nonmagnetic composites such as TaCu and RuCu degrade the MR ratio. The NOL-thickness dependence of the MR ratio is also measured. It is presented that the CoFe(B) NOL thicker than 1 nm greatly enhances the MR ratio. Nominal-thickness dependence of residual magnetic moment of the NOLs shows that partially oxidized CoFe(B) layers are most effective for the MR enhancement. Little degradation of the free-layer response to an applied magnetic field by the NOL insertion has been observed. From the current-voltage (I-V) characteristic, the electronic transport is revealed to be dominated by metallic conduction rather than tunneling. It suggests that the enhancement stems from the conduction through pinholes.