A Co-SiO$_2$Granular Material as a New Current-Confining Layer for Current Perpendicular-to-Plane Spin Valves

We have investigated a possibility of Co-SiO
₂
granular material as a current-confining layer of confined current path (CCP) type-current perpendicular-to-plane (CPP) spin valves (SVs). A resistance-area (RA) product can be controlled by a composition and a thickness of the Co-SiO
₂
granular layer, and it showed a higher controllability compared to a conventional oxidized metal current-confining layer. The CPP-SV with Co-SiO
₂
granular layer performed at a relatively large MR ratio of 5.7% with a RA of 1 Omegamum
²
and showed a potential of 5% with 500 mOmegamum
²
. This indicates a role of the Co-SiO
₂
granular layer as a current-confining structure. Although a tolerance to an applied voltage is insufficient at this stage, a granular material as a current-confining layer, such as Co-SiO
₂
, will open a door to a realization of CPP-SV magnetic recording heads for an ultrahigh-density recording system