A magnetic sensor or a magnetic head using a spin-valve type magneto-resistive effect (hereinafter referred to as an “SV type GMR”) element or a tunnel type magneto-resistive effect (hereinafter referred to as a “TN type MR”) element is able to detect a change of an external magnetic field based upon a magnetic resistance change generated by a change of a relative angle between a free layer and a fixed layer whose magnetization is fixed by an antiferromagnetic layer when the magnetization of the free layer made of a soft magnetic material is rotated in response to the external magnetic field.
In this case, in order to detect the external magnetic field at a high efficiency, by a method such as film deposition, annealing in the magnetic field, a uniaxial magnetic anisotropy is given to the free layer in the direction perpendicular to the direction in which an external magnetic field is introduced. As a consequence, although the magnetization of the free layer tends to orient in the two directions extending along this magnetic anisotropy (the forward direction or the reverse direction relative to the magnetic field to which the anisotropy is given), which direction of the above two directions the magnetization of the free layer is oriented without application of the external magnetic field is not prescribed. As a result, the above-mentioned magnetic sensor and the above-mentioned magnetic head cannot detect the change of the external magnetic field with an excellent reproducibility.
On the other hand, at the end portion of the free layer in the direction perpendicular to the aforementioned magnetic anisotropy direction (hereinafter referred to as a “side end portion”), the magnetization becomes difficult to orient in the magnetic anisotropy direction due to an antimagnetic field so that a magnetic domain occurs, which causes a so-called Barkhausen noise which causes the rotation of the magnetization to become discontinuous when the magnetization is rotated in response to the external magnetic field.
Accordingly, when the bias magnetic field is applied to the free layer in one direction of the above-mentioned magnetic anisotropy direction in an opposing relation to the side end portion of the free layer, under the condition that other magnetic field is not applied to the free layer, the free layer is nucleated as a single magnetic domain by confining its magnetization direction in a constant direction. As a result, the occurrence of the magnetic domain in the above-mentioned free end of the free layer can be avoided, the Barkhausen noise can be avoided, and the resistance change of the magneto-resistive effect element can be reproduced by the detection magnetic field with an excellent reproducibility and at an excellent stability.
Although this bias magnetic field needs a magnetic field intensity high enough to nucleate the free layer as the signal magnetic domain, when the intensity of the bias magnetic field is too high, a rotation angle at which the magnetization of the free layer is rotated in response to the external magnetic field becomes too small so that the sensitivity of the magneto-resistive effect element is lowered unavoidably. Therefore, the material and film thickness of the hard magnetic layer are selected in such a manner that the sensitivity of the magneto-resistive effect element becomes appropriate.
When the magneto-resistive effect element has a so-called CPP (Current Perpendicular to Plane) configuration in which a sense current flows in the direction perpendicular to the film plane of a magneto-resistive effect element body, i.e., in the direction perpendicular to the film plane of the free layer 1 as shown in FIG. 12, a current magnetic field HI generated in the free layer by this sense current Is is generated so as to circulate along the film plane.
At that time, at the respective central portions of a front end 1F of the free layer 1 and a rear end 1R on the opposite side of the front end, which is the side into which a detection magnetic field is introduced, the current magnetic fields become parallel to the direction in which the bias magnetic field HB is applied and also become opposite to each other.
Accordingly, as mentioned before, when the bias magnetic field HB is applied to the free layer of the magneto-resistive effect element MR, the current magnetic field HI acts in the direction in which the bias magnetic field HB is increased in intensity and also acts in the direction in which the bias magnetic field is decreased in intensity at any one of the center of the front end of the free layer and the center of the rear end of the free layer.
Therefore, in order to nucleate the free layer as the single magnetic domain, a bias magnetic field having an intensity high enough to prevent the bias magnetic fields from being canceled out should be applied to the portion in which the current magnetic field HI acts in the direction in which the intensity of the bias magnetic field is decreased.
However, this bias magnetic field becomes too high in intensity at the portion in which the current magnetic field acts in the direction in which the intensity of the bias magnetic field is increased, so that a sensitivity at this portion is lowered, accordingly, the output of the magneto-resistive effect element is decreased.