As a reading element of a thin film magnetic head, a magneto resistance (MR) element made with a multilayer film is known. Conventionally, a current in plane (CIP) element, in which a sense current flows in a direction in plane with a film surface, has been primarily utilized. Recently, in order to enable further high density recording, a current perpendicular to the plane (CPP) element, in which a sense current flows in a direction orthogonal to a film surface, has been developed. As elements of this type, a tunnel magneto-resistance (TMR) element in which a TMR effect is utilized and a current perpendicular to the plane—giant magneto resistance (CPP-GMR) element in which a GMR effect is utilized have been known.
As an example of the GMR element or the TMR element, there is an element including a spin valve film (hereafter, referred to as SV film). The SV film includes a pinned layer of which a magnetization direction is pinned with respect to an external magnetic field, a free layer of which a magnetization direction varies corresponding to the external magnetic field, and a spacer sandwiched by the pinned layer and the free layer. The SV film is sandwiched by a pair of shields that are electrodes for supplying the sense current.
In a typical CPP element, hard magnetic layers are disposed via insulation films on both sides of the SV film in a track width direction. The hard magnetic layers are referred to as bias magnetic layers. The bias magnetic layers apply a bias magnetic field to the free layer such that the free layer is formed as a single domain layer. Such a single domain free layer has advantages that linearity of resistance variation is improved corresponding to an external magnetic field variation and that simultaneously Barkhausen noise is suppressed. Magnetization directions of the bias magnetic layers are pinned in the track width direction. In the present specification, the track width direction means a direction that is parallel to a track width direction of a recording medium when a slider including the MR element faces the recording medium.
However, in accompaniment with an improvement in a recording density of a recent magnetic recording medium, the thin film magnetic head has a so-called side reading problem in that magnetic information leaked from adjacent tracks is also read.
JP 2005-353666A discloses a thin film magnetic head in which soft magnetic layers are disposed on both sides of an MR element in a track width direction to cope with the side-reading problem. Since the soft magnetic material absorbs magnetic flux from adjacent tracks, the effect of noise due to the magnetic flux from the adjacent tracks is suppressed. As a result, a thin film magnetic head is provided that is compatible with a recording medium of high recording density.
However, these soft magnetic layers do not function to apply a bias magnetic field to the MR element. Accordingly, in JP 2005-353666A, the MR element is designed to include two free layers in each of which a magnetization direction varies corresponding to an external magnetic field and an antiferromagnetic coupling layer disposed between the free layers, and the antiferromagnetic coupling layer functions such that one free layer and the other free layer antiferromagnetically interact each other. As described above, the antiferromagnetic coupling layer provides a self bias function to both of the free layers. However, sufficient bias may not be applied to the free layers with such a bias function. Also, since a material of an antiferromagnetic coupling layer as a spacer is limited to a special one, it becomes difficult to improve the performance of the MR element.
As described above, it is difficult to apply sufficient bias to the free layers while maintaining the function of a side shield. Therefore, another configuration is desired in which sufficient bias is applied to the free layers maintaining the function of the side shield.