1. Field of the Invention
The present invention relates to a so-called spin-valve type thin film element in which electric resistance is varied by the relation between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer being affected by external magnetic field, especially to the spin-valve type thin film element in which the relative angle between magnetization of the pinned magnetic layer and magnetization of the free magnetic layer is made to be properly adjustable, and to a method for manufacturing the same.
2. Description of the Related Art
FIG. 6 is a schematic drawing of the conventional structure of the spin-valve type thin film element.
The spin-valve type thin film element is a kind of GMR (giant magnetoresistive) element taking advantage of giant magnetoresistance effect for sensing recording magnetic filed from recording media such as a hard disk.
A free magnetic layer 10, a non-magnetic conductive layer 11, a fixed magnetic layer (a pinned magnetic layer) 3 and an anti-ferromagnetic layer 12 are layered in this spin-valve type thin film element, on both sides of which hard bias layers 5, 5 are formed.
Usually, a Fe--Mn (iron-manganese) alloy film or Ni--Mn (nickel-manganese) alloy film is used for the anti-ferromagnetic layer 12, a Ni--Fe (nickel-iron) alloy film is used for the pinned magnetic layer 3 and free magnetic layer 10, a Cu (copper) film is used for the non-magnetic conductive layer 11 and a Co--Pt (cobalt-platinum) alloy is used for the hard bias layers 5, 5.
As shown in FIG. 6, magnetization of the pinned magnetic layer 3 is put into a single magnetic domain state along the Y-direction (the direction of leakage magnetic field from the recording medium; the height direction) due to exchange anisotropic magnetic field with the anti-ferromagnetic layer 12 while magnetization of the pinned magnetic layer 3 is aligned along the X-direction by being affected by the bias magnetic field from the hard bias layers 5, 5.
Detecting current (sensing current) is imparted to the pinned magnetic layer 3, non-magnetic conductive layer 11 and free magnetic layer 10 from the conductive layer (not shown) formed on the hard bias layers 5, 5. While the scanning direction of the recording medium such as a hard disk is along the Z-direction, magnetization of the free magnetic layer 10 turns to the Y-direction from the X-direction when a leakage magnetic field is applied along the Y-direction from the recording medium. Electric resistance is changed depending on the relation between fluctuation of the magnetization direction in this free magnetic layer 10 and pinned magnetization direction of the pinned magnetic layer 3, sensing the leakage magnetic field from the recording medium due to voltage variation based on this electric resistance change.
The method for manufacturing the spin-valve type thin film element shown in FIG. 6 will be described below.
Firstly, the free magnetic layer 10, non-magnetic conductive layer 11, pinned magnetic layer 3 and anti-ferromagnetic layer 12 are successively layered. When the anti-ferromagnetic layer 12 is formed of the Fe--Mn alloy, the film forming step is carried out in a magnetic field along the Y-direction shown in the drawing. When the anti-ferromagnetic layer 12 is formed of the Ni--Mn alloy, on the other hand, the layer is annealed in a magnetic field along the Y-direction after forming the film.
An exchange anisotropic magnetic field (Hex) is generated at the interface between the anti-ferromagnetic layer 12 and pinned magnetic layer 3, magnetization of the anti-ferromagnetic layer 12 being fixed after being put into a single magnetic domain state along the Y-direction shown in the drawing.
Then, the layer structure is patterned so that the width of each layer of the anti-ferromagnetic layer 12, pinned magnetic layer 3, non-magnetic conductive layer 11 and free magnetic layer 10 is to be approximately the same as the track width Tw, followed by forming the hard bias layers 5, 5 on both sides of the four layers from the anti-ferromagnetic layer 12 to the free magnetic layer 10.
Once the hard bias layers 5, 5 are magnetized along the X-direction shown in the drawing, magnetization of the free magnetic layer 10 is aligned along the X-direction due to the bias magnetic field along the X-direction from the hard bias layer, setting the relative angle between magnetization of the free magnetic layer 10 and magnetization of the pinned magnetic layer 3 to about 90.degree..
However, some problems as described below arise in the conventional spin-valve type thin film element shown in FIG. 6.
While magnetization of the pinned magnetic layer 3 is fixed by being put into a single magnetic domain state as described previously, the hard bias layers 5, 5 magnetized along the X-direction are provided on both sides of the pinned magnetic layer 3. Therefore, magnetization at both sides of the pinned magnetic layer 3 is especially affected by the bias magnetic field from the hard bias layers 5, 5, making it difficult to be fixed along the Y-direction shown in the drawing. FIG. 7 is a schematic drawing illustrating the state. FIG. 7 is a top view of the pinned magnetic layer 3 and hard bias layers 5, 5.
Magnetization A at the central region of the pinned magnetic layer 3 is directed toward the Y-direction as shown in FIG. 7 because it is hardly affected by the influence of the bias magnetic field along the X-direction of the hard bias layers 5, 5 owing to a spaced apart relation to the hard bias layers 5, 5.
On the contrary, magnetization B and C at both end regions of the pinned magnetic layer 3 are so strongly affected by the bias magnetic field along the X-direction from the hard bias layers 5, 5 that magnetization is pinned by being inclined toward the X-direction from the Y-direction.
Accordingly, magnetization of the pinned magnetic layer 3 is not orthogonal to magnetization of the free magnetic layer 10 because the former is not pinned along the Y-direction in the conventional spin-valve type thin film element, making it impossible to obtain desirable micro-track asymmetry in the vicinity of both ends. Micro-track asymmetry as used herein refers to horizontal asymmetry of the reproduced output waveform measured at a minuter track width than the actual track width, giving a horizontally symmetric regenerated output waveform when the micro-track asymmetry is close to zero.
When the degree of micro-track asymmetry is increased to deteriorate it, on the contrary, sensing of the track position can not be accurately carried out to readily cause a servo-error.
Moreover, because all magnetization of the pinned magnetic layer within the track width Tw is not fixed along the Y-direction, magnetic barriers are created at the site having different magnetization direction to easily generate Barkhausen noise.