Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-01-23
2004-10-19
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120
Reexamination Certificate
active
06807033
ABSTRACT:
BACKGROUND OF INVENTION
Giant magnetoresistive (GMR) materials are materials whose electrical resistance changes when brought in contact with a magnetic field. Because of this property, GMR materials are often used in the read element of a read/write head used to read data recorded on a high-density magnetic disk. Unlike inductive heads in which the data bit on the medium induces the current across a gap, the GMR mechanism is an active element with current flowing through it. The magnetic orientation of the bit increases the resistance in a thin-film, magnetic layer of the GMR read head, and a read circuit coupled to the GMR read head detects the difference in current due to the increased resistance. Because GMR heads are more sensitive to weaker fields than the earlier inductive read coils, GMR read heads are widely used in magnetic data storage systems because as storage capacity increases, the bit gets smaller and its magnetic field becomes weaker.
GMR heads typically include additional thin films in the sensing element to facilitate the change in resistance caused by a magnetic field. A typical GMR read head includes a GMR sensing layer sandwiched between two shield layers. The GMR sensing layer is typically formed in a patterned multilayer structure including at least a non-magnetic metal layer sandwiched by two ferromagnetic layers. When the magnetic moments of the ferromagnetic layers are parallel, the GMR sensing layer has a low electrical resistance. Conversely, when the magnetic moments of the ferromagnetic layers are anti-parallel, the GMR sensing layer has a high electrical resistance. The resolution of the read element is inversely proportional to the distance (or gap) between the shield layers. Accordingly, the smaller the gap (or window), the greater the resolution of the read element, hence permitting the data to be recorded more densely on the recording medium.
One known type of high-density read head design including a GMR sensing layer is a spin valve read head. In this structure, at least one anti-ferromagnetic layer is formed adjacent to one of the ferromagnetic layers of the GMR sensing layer to pin the magnetization of that ferromagnetic layer such that the direction of the magnetic spin of the pinned ferromagnetic layer is fixed in the range of several tens to several hundreds Oersted (Oe) in magnetic field. On the other hand, the direction of the magnetic spin of the free ferromagnetic layer is freely varied by an external magnetic field. As a result, there can be achieved a magnetoresistance change ratio of two to five percent in a small magnetic field range.
According to spin valve read head designs, the anti-ferromagnetic layer must be sufficiently sized to pin the magnetization of the pinned ferromagnetic layer. Accordingly, there is a practical limit to how thin the anti-ferromagnetic layer may be fabricated, preventing further reduction of the shield-to-shield spacing, hence limiting the linear recording density. For current spin valve and advanced spin valve head designs, the anti-ferromagnetic layer typically has a thickness greater than 15 nm. As a result, the width of the GMR element of current and advanced spin valve head designs is ordinarily 30 nm or greater, which is too wide for higher density applications, such as on the order of 100 Gbits/sq inch.
In addition, with current spin valve head designs the wing region of the GMR element may detect the magnetic field from a track adjacent to the track being read by the active region of the GMR element. This phenomenon is sometimes referred to as “side-reading” and is undesirable because it increases the magnetic susceptibility of the read head. In current GMR read heads it is difficult to suppress side-reading yet maintain the sensitivity of the active region of the GMR element. This is an especially acute problem, as increasingly narrower active regions are needed as storage densities continue to increase.
BRIEF SUMMARY OF THE INVENTION
According to one embodiment, the present invention is directed to a magnetic sensor. The magnetic sensor includes a synthetic antiferromagnetic (SAF) layer having first and second wing regions and an active region therebetween. The SAF layer includes two ferromagnetic layers and a non-magnetic metal layer therebetween such that there exists an anti-parallel magnetic coupling between the two ferromagnetic layers.
The second ferromagnetic layer is only patterned onto the non-magnetic metal layer in the wing region portions thereof and is of adequate thickness such that the magnetic susceptibility of the wing region portions of the first ferromagnetic layer is substantially zero when a magnetic field is present only in the wing regions.
The magnetic sensor may be used in various devices such as, for example, spin valve (CIP/GMR) read heads, tunnel junction heads, and CPP/GMR read heads.
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Carnegie Mellon University
Kirkpatrick & Lockhart LLP
Klimowicz William
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