In recent years, the need to increase the processing speed and the recording capacity in recording on magnetic disk media in magnetic disk apparatuses (HDD apparatuses) or the like has increased. Schemes to develop high-density magnetic recording media are now being contrived and pursued. With this movement, reproducing heads used for reproduction from reproducing tracks of smaller widths and having larger reproduction outputs in comparison with conventional thin-film magnetic heads are being developed. It is certain that this tendency will be accelerated in future.
Spin-valve-type magnetoresistive-effect films are presently being used ordinarily in magnetoresistive-effect devices for reproducing heads. A spin-valve magnetoresistive-effect film has a basic structure formed of a free magnetic layer, a nonmagnetic layer, a fixed magnetic layer and an antiferromagnetic layer.
A structure designed to increase the recording density by increasing the sensitivity of such a spin-valve magnetoresistive-effect film is known. For example, Japanese Patent Laid-Open No. 6-236527 discloses a structure in which the thickness of a free magnetic layer is increased and an electroconductive layer is formed adjacent to and at the back of the free magnetic layer to increase the mean free path.
Also, “Kamiguchi et al “CoFe SPECULAR SPIN VALVES WITH A NANO OXIDE LAYER” Digests of Intermag 1999, DB-01, 1999” discloses a technique of obtaining a so-called specular reflection effect by inserting between a free layer and a fixed magnetic layer an extremely thin oxide layer called NOL (Nano Oxide Layer) and causing conduction electrons to be reflected by the interface between the oxide layer and a metal layer. In this arrangement, a spin valve film is formed like a pseudo artificial grating film, whereby the MR ratio can be improved.
Japanese Patent Laid-Open No. 7-262520 discloses a report saying that when a GMR device constituted by a multilayer film uses a CPP (current perpendicular-to-the-plane) mode in which a current is caused to flow perpendicularly to a film surface, it has a change in resistance twice that in the conventional CIP (current in-the-plane) mode in which a current is caused to flow parallel to the film surface. An increasing number of adaptations to CPP-spin valve films are being made.
Under circumstances where there will be a stronger demand for increasing the recording density of magnetic recording media, there is a challenge to further increase the sensitivity of magnetoresistive films in magnetoresistive-effect devices for reproducing heads in order to reproduce signals recorded at short wavelengths on magnetic recording media.