1. Field of the Invention
The present invention relates to a magnetoresistance effect element using a magnetic multi-layer film having a giant magnetoresistance effect, and a magnetic head and a magnetic recording device using the same.
2. Description of the Related Art
In a magnetic recording device such as an HDD, in order to enhance a recording density, a tendency of narrowing a recording track width of a recording medium is in progress. To compensate for the decrease of read output due to this narrowing of the recording track width, a demand for a magnetic head (MR head) employing a highly sensitive magnetoresistance effect element(MR element) is becoming strong. In particular, an MR head which is consisting of a magnetic multi-layer film stacked on a substrate in turn of a ferromagnetic layer (hereinafter refer to as a free layer) of which magnetization rotates according to a signal magnetic field, a non-magnetic layer, a ferromagnetic layer of which magnetization is pinning (hereinafter refer to as a pinned layer), and an antiferromagnetic layer for pinned the magnetization of the pinned layer, and displaying a giant magnetoresistance effect, is attracting attention.
In an MR head employing a spin valve film, Barkhausen noise due to discontinuous shift of magnetic domain walls of a free layer is a problem when putting it into practical use. To circumvent such a problem, a so-called overlaid structure is proposed, in which, as shown in FIG. 21, on area off a track width Wt of a spin valve film 1, a pair of magnetic hard layers 2 are disposed in advance as hard magnetic biasing films and both edge portions of the spin valve film 1 are stacked on the pair of hard magnetic layers 2.
In an overlaid structure, an exchange coupling is caused through stacking of a spin valve film 1 and magnetic hard layers 2. By extinguishing a magnetic domain of a free layer with a bias magnetic field due to mainly exchange coupling, Barkhausen noise is suppressed. An MR head of such an overlaid structure is expected because a high read output can be obtained, and an excellent off-track profile is displayed (IEEE Trans. on Mag. Vol. 32,3363(1996)).
Further, in a spin valve MR head shown in FIG. 21, a spin valve film 1 consists of a free layer 3, a non-magnetic layer 4, a pinned layer 5 and an antiferromagnetic layer 6. On the spin valve film 1, a pair of electrodes 7 for providing a sense current thereto are formed. A spin valve film 1 is interposed between a pair of magnetic shield layers 9a, 9b disposed above and below through magnetic gaps 8a, 8b, respectively. These constitute a shield type MR head. For enhancing sensitivity of a spin valve film 1, a Co containing ferromagnetic material such as a CoFe alloy is effective as a free layer 3 and a pinned layer 5.
Now, in order to respond to a further high densification of a magnetic recording density, even in a spin valve MR head, further narrowing of gaps (thinning of magnetic gaps 8a, 8b) is demanded. When an overlaid structure is applied in such a narrow gapped MR head as a bias structure, there is a problem that an effective bias strength can not be obtained. That is, even if a bias strength is tried to be heightened by increasing film thickness of magnetic hard layers 2 as a hard magnetic biasing film, since bias magnetic field leaks toward magnetic shield layers 9a, 9b, an effective bias strength can not be obtained.
In particular, when an overlaid structure is applied to a spin valve film possessing a non-magnetic under layer such as Ta, a magnetic coupling force between a free layer and a hard magnetic layer becomes weak to decrease a biasing effect of a bias magnetic field based on an exchange coupling. Thereby, a suppression effect of Barkhausen noise is further deteriorated.
As described above, in a bias structure of an MR head employing a spin valve film, an overlaid structure in which portions outside from a magnetic field detecting portion of a spin valve film are stacked on hard magnetic layers, due to the narrowing of gap or track of an MR head, is becoming difficult to supply effectively a biasing magnetic field to a free layer. Further, a spin valve film is under study to use as a magnetic memory device such as a magnetoresistance effect memory (MRAM). As to an MRAM, though there is not found so much mentioning of a structure with a biasing film, in some cases, a biasing film may become necessary. In such a case, a technology for eliminating noise with stability even when a size of a unit-cell is decreased is demanded.