Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-02-02
2004-10-19
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06807032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to read elements for recording heads for use with magnetic recording media. Specifically, the invention relates to a combined shield/electrical lead for the read element having minimized Anisotropic Magneto-Resistance (AMR) effect.
2. Description of the Related Art
Magneto-resistive (MR) and giant magneto-resistive (GMR) read elements for reading from magnetic recording media have been proposed to overcome the limited sensitivity of inductive reading 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 sense current. A constant resistance level indicates a binary “0,” and a changing resistance level indicates a binary “1.”
Spin valves have also been used to increase the read sensitivity of recording heads. A typical spin valve comprises a pair of ferromagnetic layers having a nonmagnetic layer therebetween, with an antiferromagnetic layer adjacent to one of the ferromagnetic layers. The antiferromagnetic layer is a material that is generally not affected by external magnetic fields, and is therefore generally considered to be nonmagnetic. However, the material has been annealed at high temperature and cooled while exposed to a magnetic field. The magnetization in the ferromagnetic layer closest to the antiferromagnetic layer will align itself with respect to the orientation of the closest layer of the antiferromagnetic material. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the orientation of the magnetiationof the free layer will change to correspond with this magnetic field. This relative change in the orientation of the magnetization of the free layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve to an applied sense current. As before, a constant resistance level indicates a binary “0” and the changing resistance level indicates a binary “1.”
Read elements are located between a pair of ferromagnetic shields for preventing the read element from being influenced by magnetic domains adjacent to the domain currently being read. The sense current for detecting changes in the resistance of the read element is applied through a pair of leads on opposing sides of the read element. This sense current may be applied either parallel to the plane of the alternating layers within the read element (CIP), or perpendicular to the plane of these alternating layers (CPP). To minimize the resistance of the electrical leads, these leads must be thick. Additionally, a typical ferromagnetic shield will exhibit an Anisotropic Magneto-Resistance (AMR) effect, wherein the resistance of the shield will change if its magnetization direction changes. Therefore, a thick insulation must be provided between the electrical leads for the read element and the ferromagnetic shields to prevent any sense current from flowing through the shields, thereby causing both changes in the resistance of the read element and changes in the resistance of the shields to be detected. The resulting sequence of thick layers increases the distance from one shield to the other, thereby reducing the maximum linear bit density within the corresponding magnetic recording media.
Accordingly, there is a need for a magnetic recording head having reduced distance between the magnetic shields for its read elements. Additionally, there is a need for a magnetic shield material having a minimized AMR effect.
SUMMARY OF THE INVENTION
The present invention is an improved recording head for use with magnetic recording media. The improved recording head includes a read element having a pair of shields for which the anisotropic magneto-resistance effect has been minimized, thereby permitting the shields to serve the additional purpose of electrical leads for the read 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 read elements, which are parallel to the trackwidth The read element is located between these shields. The shields also form electrical leads for the read elements, thereby eliminating the necessity of a separate electrical lead, and insulation between the electrical lead and the magnetic shield.
Presently available magnetic shields are generally combinations of Ni, Fe, and Co. Such magnetic shields have too much variation in resistance with changing magnetization direction within the material. This is known as the Anisotropic Magneto-Resistance (AMR) effect. A sense current passing through these combination lead/shields and the read element would measure the change in resistance not only in the read elements, but also within the lead/shields. Therefore, a lead/shield of the present invention includes additional elements that will reduce the AMR effect. Examples of additional materials include Cu, Cr, Mn, Ti, Au, Ag, V, Zr, Nb, Ta, and W. Preferred embodiments of lead/shields of the present invention include both alloys of these elements within the crystal structure of the magnetic shields material, and laminated structures wherein these elements are layered within the magnetic shields. Another preferred embodiment may include a separate, low resistivity lead outside the lead/shields, on opposing sides of the read element and associated shields. The low resistance of these leads will cause current to travel through these leads instead of through the magnetic shields for the maximum distance possible, traveling through the shields for the smallest distance possible. This will result in current flowing through the magnetic shields perpendicular to the surface of the read element, thereby yielding constant shield resistance.
Although the present invention may be used with any presently known read elements, it is particularly useful with low resistance read elements such as giant magneto-resistive (GMR) elements and spin valves. The invention may still be used with high resistance read elements such as tunnel magneto-resistive (TMR) read elements.
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 sense current. A constant resistance level generally indicates a binary “0,” and a changing resistance level generally indicates a binary “1.”
A typical spin valve comprises a p
Batra Sharat
Covington Mark William
Minor Michael Kevin
Rottmayer Robert Earl
Seigler Michael Allen
Cao Allen
Pietragallo Bosick & Gordon
Queen, II, Esq. Benjamin T.
Seagate Technology LLC
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