Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-04-14
2001-02-27
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C360S324100
Reexamination Certificate
active
06194896
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of controlling magnetic characteristics of a magnetoresistive effect (MR) element biased by an anti-ferromagnetic material layer, for example, a giant magnetoresistive effect (GMR) element such as a spin valve MR element, or a tunneling magnetoresistive effect (TMR) element. The present invention also relates to a method of controlling magnetic characteristics of a magnetic head with the MR element, a magnetic head device with the MR element, and a magnetic disk unit with the device.
DESCRIPTION OF THE RELATED ART
Recently, thin film magnetic heads with MR elements based on spin valve of GMR characteristics are proposed in for example U.S. Pat. Nos. 5,206,590 and 5,422,571, in order to satisfy the requirement for ever increasing data storage densities in today's magnetic storage systems like magnetic disk units. The spin valve thin film structure includes first and second thin film layers of a ferromagnetic material separated by a thin film layer of non-magnetic conductive material, and an adjacent layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer to provide exchange coupling bias magnetic field by exchange coupling at the interface of the layers. The magnetization direction in the second ferromagnetic layer is constrained or maintained by the exchange coupling, hereinafter the second layer is called “pinned” layer. On the other hand, the magnetization direction of the first ferromagnetic layer is free to rotate in response to an externally applied measurement magnetic field, hereinafter the first layer is called “free” layer. The direction of the magnetization in the free layer changes between parallel and anti-parallel against the direction of the magnetization in the pinned layer, and hence the magnetoresistive effect greatly changes and GMR characteristics are obtained.
The output characteristic of the spin valve MR element depends upon the angular difference of magnetization between the free and pinned layers. The direction of the magnetization of the free layer is free to rotate in accordance with an external magnetic field. That of the pinned layer is fixed to a specific direction by the exchange coupling between the layer and adjacently formed anti-ferromagnetic layer.
In order to provide exchange coupling between the anti-ferromagnetic layer and the ferromagnetic layer (pinned layer), a process of temperature annealing under an external magnetic field with a specific direction (pin anneal process) is implemented. The pin anneal process is done as follows, first the temperature is elevated up to the Neel point at which temperature magnetization order in the anti-ferromagnetic material layer will be destroyed, and then cooled down to room temperature under a certain magnetic field strength with a specific direction for the exchange coupling. By this pin anneal process, the exchange coupling is regulated at the interface of the pinned and anti-ferromagnetic layers toward the direction of the externally applied magnetic field.
Thus, to provide the exchange coupling between the anti-ferromagnetic and pinned layers, it is necessary in the conventional art to additionally execute a temperature annealing under application of magnetic field, whereby not only the manufacturing processes become complicated but also the manufacturing cost is increased.
Also, to simultaneously carry out the same magnetization process for a plurality of magnetic heads, it is necessary to uniformly align the directions of the external magnetic fields that are applied to the magnetic heads. Therefore, the temperature annealing under magnetic field is usually executed at a wafer process stage of the magnetic heads or at a bar stage where a wafer is cut into some bar-shaped blocks. This is because carrying out such pin anneal process under magnetic field after separating the bar block into the individual magnetic heads is troublesome to define the magnetization directions and becomes non-effective. However, even if the magnetic heads are in any state such as in a state where they are individually separated, it is naturally desirable that the process of providing the exchange coupling between the anti-ferromagnetic and pinned layers can be easily executed.
When some electric charges are applied to the terminals of the MR elements due to certain reason during manufacturing processes such as the wafer process of the magnetic heads and the mechanical working process, or during assembling processes of completed heads to the magnetic disk unit, the pinned direction of the spin valve MR element may be changed or inverted and thus various characteristics of the head may vary causing incorrect reproduction of the magnetically recorded signal. The change or inversion of the pinned direction may be caused by heat and magnetic field generated by the applied electric charges.
As aforementioned, if the pinned direction changes, the angle between the magnetization directions in the pinned and free layers also changes causing the output characteristics to vary. Thus, it is very important in the magnetic head with the spin valve MR element to correctly maintain or fix the pinned direction. However, when the pinned direction changes after separating the bar block into the individual magnetic heads, it is very difficult as mentioned above to provide the exchange coupling between the anti-ferromagnetic and pinned layers again and return the pinned direction to the correct direction. Therefore, such processes have not been executed in the conventional technique, and the resulting magnetic heads have been treated as failed components.
U.S. Pat. No. 5,650,887 discloses a pinned layer magnetization reset system which applies a rectangular waveform current to a spin valve MR sensor so as to heat the sensor and to generate a magnetic field around the pinned layer and thus controls the pinned direction. However, this reset system cannot execute sufficient temperature and magnetic field control during cooling stage after heating the spin valve MR element. Thus, it is difficult to return the output characteristics of the spin valve MR element back to its desired state.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of controlling magnetic characteristics of a MR element, a method of controlling magnetic characteristics of a magnetic head with the MR element, a magnetic head device with the MR element, and a magnetic disk unit with the device, whereby control of the pinned direction in the MR element can be extremely easily executed without adding new processes even after the magnetic heads are individually separated.
It is another object of the present invention to provide a method of controlling magnetic characteristics of a MR element, a method of controlling magnetic characteristics of a magnetic head with the MR element, a magnetic head device with the MR element, and a magnetic disk unit with the device, whereby, ideal temperature control and magnetic field control can be executed during the above-mentioned control of the pinned direction in the MR element.
According to the present invention, a method of controlling magnetic characteristics of a MR element and a method of controlling magnetic characteristics of a magnetic head with the MR element utilizing exchange coupling magnetization, include a step of supplying discrete rectangular waveform currents or a rectangular waveform current to the MR element so as to generate magnetic field in a desired direction and to generate Joule heat, the generated magnetic field and the generated joule heat being applied to the MR element, and a step of controlling a duty ratio of the discrete rectangular waveform currents or a time constant of the falling of the rectangular waveform current so that a temperature of the MR element is controlled under a desired temperature change characteristics, whereby a magnetization direction caused by the exchange coupling in the MR element is aligned to a desired direction.
In the
Inage Kenji
Maeda Toshiaki
Takahashi Masato
Arent Fox Kintner & Plotkin & Kahn, PLLC
Patidar Jay
TDK Corporation
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