Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-04-17
2004-08-10
Hudspeth, David (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
Reexamination Certificate
active
06774626
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and method for measuring the properties of a magnetic reproducing head that reads data from a data recording medium. The present invention, more particularly, relates to a device and method for measuring a local magnetic property of a magnetic reproducing head.
BACKGROUND AND MATERIAL INFORMATION
A magnetic reproducing head is a device to read data stored in a magnetic disk mounted in a disk storage unit, for example. Conventionally, operating characteristics of the magnetic reproducing head are evaluated by actually reading the data from the magnetic disk after the head is mounted in the disk storage unit. However, with the increase of magnetic density in a magnetic disk, a magnetic reproducing head has been downsized in recent years. As a result, it has become more difficult to check the quality of the magnetic reproducing head according to a conventional method of measuring operating characteristics.
In consideration of these circumstances, Japanese laid-open patent publication No. 2000-20929 (Tokkai 2000-20929) discloses a device to measure the magnetic property distribution on a measurement surface of a magneto-resistive head (hereinafter referred to as ‘MR head’), which is a kind of a magnetic head, applying the principle of an atomic force microscope (hereinafter referred to as ‘AFM’). The MR head employs an element having a magneto-resistive effect, electric resistance of which change with the strength of a magnetic field externally applied, as its head.
Originally, the AFM is a device to observe the shape of a microscopic area by scanning the surface of a matter to be observed using a magnetic tip that oscillates at a predetermined amplitude. So, in the Japanese laid-open patent publication, a magnetic element is employed as the tip to measure the magnetic property of the MR head using the AFM.
That is, the magnetic property distribution of the MR head is measured by utilizing the phenomenon in which a magnetic field applied to the MR head by this magnetic tip changes with the tip's oscillation over the surface to be measured. The measurement is executed in a manner shown below:
(1) The MR head is supplied with a constant current from a constant current source.
(2) The magnetic tip oscillating at a specific frequency is brought close to the MR head.
(3) As a value of resistance of the MR head changes with the magnetic field applied by the magnetic tip, a voltage across the MR head changes.
(4) Amplitudes and phases of both fundamental frequency component of the tip's oscillation and its secondary harmonic component are measured by executing a synchronous detection to the voltage across the MR head using a lock-in amplifier.
(5) A distribution of each component is measured by repeating the same synchronous detection all over a measurement surface of the MR head.
(6) Some constant magnetic fields having different strength are applied externally to the MR head and consequently some magnetic property distributions corresponding to the strength of the applied magnetic field are measured.
As described above, the Japanese laid-open patent publication discloses a property measuring device effective in measuring a magnetic property distribution within a measurement surface. However, in order to fully evaluate the operating characteristics of a magnetic reproducing head, it is demanded to measure local magnetic properties within the measurement surface in addition to its magnetic property distribution.
Further, in the property measuring device, an oscillation/amplitude signal of a cantilever is transformed to a signal having a constant amplitude by an automatic gain controller and the transformed signal is supplied to a lock-in amplifier as a reference signal. However, the signal having a constant amplitude is not desirable as the reference signal from the viewpoint of the principle of synchronous detection because a Q factor of this signal is apt to lower due to thermal oscillation of the cantilever.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a device and method for measuring properties of a magnetic reproducing head that substantially obviates one or more of problems due to limitations and disadvantages of the prior art.
In accordance with the purpose of the present invention, as embodied and broadly described, the present invention is directed to a device for measuring a magnetic property of a magnetic reproducing head at a measurement point thereon. The device comprises means for applying a first magnetic field which oscillates at a predetermined oscillation frequency to the measurement point, means for applying a second magnetic field of which strength changes slower compared with the oscillation frequency of the first magnetic field to the measurement point, means for detecting a signal generated by the magnetic reproducing head according to the total strength of the first magnetic field and the second magnetic field, and means for measuring the detected signal's dependency on applied magnetic field strength.
Also in accordance with the present invention, there is provided a device for measuring a magnetic property of a magnetic reproducing head at a measurement point thereon. The device comprises means for applying a first magnetic field which oscillates at a predetermined oscillation frequency to the measurement point, means for applying a second magnetic field of which strength changes slower compared with the oscillation frequency of the first magnetic field to the measurement point, means for detecting a signal generated by the magnetic reproducing head according to the total strength of the first magnetic field and the second magnetic field, means for extracting amplitude components synchronizing with the oscillation frequency from the signal, and means for calculating changes of the signal against the total magnetic field strength based on the extracted amplitude components.
Further in accordance with the present invention, there is provided a device for measuring both a shape property of a measurement surface of a magnetic reproducing head and a magnetic property on a measurement point within the measurement surface. The device comprises a probe at least a part of which is made of a magnetic substance, means for oscillating the probe at a predetermined amplitude in the normal direction to the measurement surface, means for moving the oscillating probe tapping the magnetic reproducing head on the measurement surface at the predetermined amplitude, and discontinuing the moving when the probe is located at the measurement point, means for detecting the probe's displacement in the normal direction to the measurement surface, means for measuring the shape property of the measurement surface based on the probe's displacement detected during the moving, means for applying a magnetic field of which strength changes slower compared with the oscillation frequency of the probe to the measurement surface while the moving is discontinued, means for detecting a signal generated by the magnetic resistive head according to the total strength of the magnetic field both by the magnetic field applying means and by the probe while the moving is discontinued, means for extracting amplitude components synchronizing with the oscillation frequency from the signal, and means for calculating changes of the signal against the total magnetic field strength based on the extracted amplitude components.
Additionally in accordance with the present invention, there is provided a method for measuring a magnetic property of a magnetic reproducing head at a measurement point thereon. The method comprises applying a first magnetic field which oscillates at a predetermined oscillation frequency to the measurement point, applying a second magnetic field to the measurement point, changing the strength of the second magnetic field slower compared with the oscillation frequency of the first magnetic field, detecting a signal generated by the magnetic reproducing head according to the
Kabushiki Kaisha Toshiba
Negroń Daniell L
Pillsbury & Winthrop LLP
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