Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-11-03
2003-02-11
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06519119
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates to giant magnetoresistive read heads. More specifically, the invention is an improved structure for a giant magnetoresistive read head having the test current applied substantially perpendicular to the plane of the read head's layers.
2. Description of the Related Art
Magnetoresistive (MR) and giant magnetoresistive (GMR) read elements for reading from magnetic recording media have been used to overcome the limited sensitivity of inductive reading. GMR technology has also been incorporated with spin-valve structures that are well known in the art. GMR read elements are generally composed of alternating layers of magnetic and nonmagnetic material, so that, when exposed to a magnetic field, the relative change in the orientation of the magnetizations in the magnetic layers alters the spin-dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the GMR head to an applied test current. A constant resistance level indicates a binary “0,” and a changing resistance level indicates a binary “1.”
Most current GMR read heads are structured so that the test current is applied in the same plane as the alternating magnetic and nonmagnetic layers (CIP). Applying the current perpendicular to the plane of these layers (CPP) has been found to increase the GMR effect.
Typical CPP GMR read elements are oriented with the alternating layers perpendicular to the recording medium's tracks, and parallel to the magnetic shields on either side of the GMR element. Such designs have limited GMR effect due to the limited number of alternating magnetic and nonmagnetic layers that will fit within the available space within the read head.
Accordingly, there is a need for a CPP GMR read element having its layers oriented perpendicular or angled with respect to the shields. Additionally, there is a need for a CPP GMR read element with increased read sensitivity. Further, there is a need for a CPP GMR element permitting storage within magnetic recording media at greater densities.
SUMMARY OF THE INVENTION
The present invention is an improved recording head for use with magnetic recording media and a method of making such a read head. The GMR read element of the present invention has a test current applied substantially perpendicular to the alternating magnetic and nonmagnetic layers of the GMR element (CPP), and is preferably oriented so that the layers are substantially perpendicular to the shields, and substantially parallel to the track. This configuration maximizes the number of layers that may be included as compared to other equivalent size GMR heads while minimizing the area perpendicular to the test current, thereby maximizing both resistance, and the change in resistance relative to total resistance with changing magnetic flux, within the GMR element.
A preferred embodiment of the present invention includes a recording head combining a read portion and a write portion. The write portion may be of either perpendicular or longitudinal configuration. A typical perpendicular recording head includes a main pole, an opposing pole magnetically coupled to the main pole, and an electrically conductive coil adjacent to the main pole. The bottom of the opposing pole will typically have a surface area greatly exceeding the surface area of the main pole's tip. Likewise, a typical longitudinal recording head includes a pair of poles, with a coil adjacent to one pole. Unlike a perpendicular recording head, a longitudinal recording head will typically use poles having bottom surfaces with substantially equal areas. In either case, electrical current flowing through the coil creates a flux through the main pole. The direction of the flux may be reversed by reversing the direction of current flow through the coil.
In some preferred embodiments, the opposing pole of the perpendicular head (or the first pole of the longitudinal head) can also form one of two substantially identical shields for the GMR read element, which are parallel to the trackwidth. The GMR read element is located between these shields. The GMR read element includes a plurality of alternating magnetic and nonmagnetic layers. Electrical contacts are electrically connected to either side of the GMR read element, also between the two shields, and are dimensioned and configured to apply current perpendicular to the plane of the various layers of the GMR element (CPP). The GMR layers may be perpendicular to the shields and trackwidth, or may be angled with respect to the shields and trackwidth. Although any angle greater than 0° and less than 90° is possible, preferred angles are between 10° and 80°. Angling the GMR element minimizes the cost of manufacture, while making the GMR element perpendicular to the shields minimizes the trackwidth. A relatively weak permanent magnet is located directly above the GMR read element, thereby orientating adjacent magnetic fields within the magnetic layers of the GMR element perpendicular to each other when the GMR element is not in close proximity to another magnetic field.
A typical magnetic recording medium includes a first layer having a plurality of magnetically permeable tracks separated by nonmagnetized transitions. If perpendicular recording is desired, the magnetic recording medium will include a magnetically permeable lower level. The lower level is magnetically soft relative to the tracks.
To read from the magnetic recording medium, the recording head is separated from the magnetic recording medium by the flying height. The magnetic recording medium is moved past the recording head so that the recording head follows the tracks of the magnetic recording medium, typically with the magnetic recording medium first passing under one shield, followed by the GMR read element, then passing under the write portion of the head pole. As the magnetic recording medium passes under the GMR element, the magnetic fields within the recording medium orient the adjacent magnetic fields within the magnetic GMR layers so that they are either parallel (corresponding to minimum resistance) or antiparallel (corresponding to maximum resistance), depending on the direction of the magnetic field being read from the recording medium. A sense current is passed through the GMR element by the contacts, thereby enabling the GMR element's resistance to be detected. A constant level of resistance is read as a binary “0,” and a change in resistance is read as a binary “1.”
The sensitivity of the GMR read element is proportional to both the number of layers present, and to the thickness of each layer. Two factors affect the sensitivity of the GMR read element: total resistance; and the magnitude of the change in resistance with changing magnetic flux relative to the total resistance. Total resistance is proportional to the length of the GMR read element (measured in the direction of current flow) divided by the area the current may travel through (measured perpendicular to the current flow). By orienting the GMR element so that the layers are oriented perpendicular to the shields and parallel to the read head's direction of travel, the number of layers across the trackwidth is maximized. Additionally, the area through which current flows is minimized, thereby further increasing resistance. The result of both of these changes is that both total resistance, and the change in resistance as a function of magnetic flux with respect to total resistance, are maximized. Using a GMR read element with greater sensitivity permits using magnetic recording media having greater storage densities.
It is therefore an aspect of the present invention to provide a GMR read element having the alternating magnetic and nonmagnetic layers angled with respect to the shields, thereby increasing sensitivity of the GMR read element and permissible storage density of the magnetic recording medium while keeping costs of manufacture minimized.
It is another aspect of the present invention to provide a GMR read element having the al
Crue Billy Wayne
van der Heijden Petrus A.
Pietragallo Bosick & Gordon
Queen, II Benjamin T.
Seagate Technology LLC
Tupper Robert S.
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