1. Field of the Invention
The present invention relates to a method of manufacturing a spin valve film including an undercoat film, a first ferromagnetic film, a second ferromagnetic film and an electrically conductive film arranged between the first and second ferromagnetic films, and also relates to a method of manufacturing a thin film magnetic head comprising such a spin valve film.
2. Description of the Related Art
In accordance with miniaturization of magnetic disk drives, a thin film magnetic head including a magnetoresistive sensor utilizing the magnetoresistive effect has been widely used as a magnetic converting element which is suitable for reading information out of a magnetic record disk having information recorded thereon with a high surface recording density owing to a reason that an output of such a magnetoresistive sensor is not affected by a relative speed between the head and the disk.
In general, as a reading magnetoresistive element, an element utilizing an anisotropic magnetoresistive effect film (hereinafter referred to AMR film) such as a permalloy film has been used so far, but recently there has been further developed a reproducing element utilizing a giant magnetoresistive effect film (referred to GMR film). Particularly, a spin valve film has been mainly utilized as GMR film. Magnetoresistive sensors using spin valve films have been described in Japanese Patent Laid-open Publication Kokai Hei 4-358310 and “IEEE TRANSACTIONS ON MAGNETICS”, Vol. 30, No. 6, November 1994. A typical spin valve film includes an undercoat film, a first ferromagnetic film, an electrically conductive film, and a second ferromagnetic film.
The electrically conductive film is sandwiched between the first and second ferromagnetic films. One of the first and second ferromagnetic films serves as a free layer which responds to an external magnetic field, and the other ferromagnetic film acts as a pinned layer having a fixed magnetic orientation.
When the first ferromagnetic film is used as the free layer, the second ferromagnetic film operates as the pinned layer, and when the first ferromagnetic film is used as the pinned layer, the second ferromagnetic film serves as the free layer. A ferromagnetic film utilized as the free layer may be formed by a NiFe film or a stack of Co film and CoFe film. A ferromagnetic film used as the pinned layer may be formed by a Co film or a CoFe film. An antiferromagnetic film is arranged adjacent to a ferromagnetic film serving as the pinned layer, and this ferromagnetic film is magnetized in one direction (being pinned) due to the exchange coupling between the antiferromagnetic film and the ferromagnetic film.
The undercoat film may be made of a suitable material which satisfies a higher magnetoresistive change rate (hereinafter referred to MR change rate), a small diffusion into a ferromagnetic film, and a higher resistance against etching.
When an external magnetic field is applied to the spin valve film, the magnetic orientation of the free layer is rotated in accordance with a magnitude of the external magnetic field. A resistance of the spin valve film is determined by an angle of a direction of magnetic orientation of the free layer with respect to a magnetic orientation of the pinned layer. A resistance of the spin valve film becomes maximum when a magnetic orientation of the free layer becomes opposite to that of the pinned layer and becomes minimum when the free layer and pinned layer have a same magnetic orientation. The external magnetic field can be sensed from a change in resistance.
The above mentioned spin valve film is manufactured by sputtering. Upon manufacturing the spin valve film, a substrate is introduced into a sputtering vacuum chamber, and successive films of the spin valve film are continuously formed by changing targets within the sputtering vacuum chamber, while sputtering is not interrupted for a meaningful or significant time period. When targets are changed, the film formation is temporarily interrupted, but its duration is too short to change a property of sputtered films.
In this known continuous film making method, a spin valve film having a high anisotropic magnetic field Hk as well as a high quality can be manufactured. The anisotropic magnetic field produced in the free layer is influenced by a magnetic field generated in the pinned layer. In the present specification, the anisotropic magnetic field Hk of the spin valve film means the anisotropic field which is magnetically influenced by the pinned layer.
The above mentioned spin valve film may be applied to magnetic sensor and nondestructive magnetic memory, and a most important application is a reading element of a thin film magnetic head. In order to increase an output read out signal from a thin film magnetic head having a spin valve film acting as a reading element, various means have been proposed and practiced.
However, output read out signals from spin valve films are limited as long as the spin valve films are manufactured by the continuous film forming process.