Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-01-06
2001-02-06
Heinz, A. J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S317000
Reexamination Certificate
active
06185077
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electromagnetic transducers and sensors, and particularly to magnetoresistive sensors.
BACKGROUND
In the field of magnetic heads for disk drives, large advances in signal sensitivity have been made in recent years with the employment of magnetoresistive sensors. Such sensors utilize elements having a resistance to electrical conduction that changes in response to an applied magnetic field, in order to read signals such as magnetic patterns on a disk. Generally such elements comprise at least one thin layer of ferromagnetic material that is magnetized in a reference direction in the absence of an applied magnetic field. As such a sensor is exposed to an applied magnetic field, the magnetization direction of that layer changes from the reference direction, and the resistance to electrical current also changes, which is measured as a signal. Various mechanisms are known for establishing the reference direction and signal bias, including the use of a permanent magnet, canted current, soft adjacent layer or an antiferromagnetic pinning layer.
Magnetoresistive sensors can include anisotropic magnetoresistive elements, giant magnetoresistive elements or spin valve elements. Spin valve sensors conventionally employ a pinned magnetic layer separated from a free magnetic layer by a conductive spacer layer. When the magnetization of the free layer is parallel to that of the pinned layer, it is believed that parallel electron spins of the magnetic layers allow conduction to occur more easily than when the magnetizations are not parallel. The magnetization of the pinned layer is conventionally held fixed by an antiferromagnetic layer that adjoins the pinned layer.
Unless the pinning force is quite strong, however, the applied magnetic field can alter the direction of magnetization of the pinned layer as well as rotating the free layer magnetization, denigrating signal resolution. Moreover, the coupling between the pinned and pinning layers becomes weaker at higher temperatures, exacerbating the problem of having a pinned layer with a magnetization that may not be fixed. Resistive heating of the sensor during operation can lead to such a breakdown. Further, a breakdown of coupling at elevated temperatures can allow a shift in the direction of magnetization of the pinned layer upon cooling, leading to further problems in reading and interpreting signals. Such a shift can also mischaracterize servo tracking information, causing heads including the sensors to have offtrack errors.
Another form of pinning that has been proposed is to use a balanced pair of oppositely magnetized layers with an extremely thin (a few angstroms thick) layer of a noble metal (ruthenium) sandwiched between the oppositely magnetized layers. This balancing can reduce the magnetic moment felt by the pair of magnetic layers compared with the moment that would be felt by only one of the magnetic layers. An antiferromagnetic layer adjoins one of the magnetized layers for pinning the sandwich. The necessity of forming extra layers, one of which must be as thin as a few atomic layers of ruthenium, however, makes large scale manufacture of this proposal extremely difficult.
SUMMARY OF THE INVENTION
We have discovered that a ferromagnetic layer pinned by an antiferromagnetic layer may not form a single domain but rather a number of microdomains. These microdomains generate signal noise, which increases along with temperature. Moreover, magnetic randomization can occur over time in the edge of the pinning layer closest to the disk, the randomization believed to be caused by repeated exposure to magnetic signals from the disk. Unfortunately, signals pass through that edge before propagating through the rest of the sensor, magnifying any defects such as randomization that are present in the edge.
The present invention provides an improved pinning structure for a magnetoresistive sensor. The improved pinning structure includes a pair of ferromagnetic material layers sandwiched about an antiferromagnetic material layer. The ferromagnetic material layers have magnetizations that are pinned in substantially opposite directions from each other, creating a stable, magnetostatically coupled structure. Moreover, the pinning of these ferromagnetic material layers by the interposed antiferromagnetic material layer is enhanced by the interaction of each major surface of the antiferromagnetic material layer with a bordering major surface of the adjacent ferromagnetic material layer. The large surface area that is pinned and the magnetostatically coupled layers synergistically reinforce each other in forming an inherently stronger pinned structure than is conventional. The problems that have been discovered with regard to edge effect randomization are ameliorated with this stable pinning structure, so that the magnetization along the edge of each pinned layer is held perpendicular to that layer, enhancing sensor output.
With the ferromagnetic material layers formed to substantially equal size and shape, the magnetic moments of each of the ferromagnetic material layers are balanced, so that the structure may experience relatively little torque in response to an applied magnetic field. Such a structure has a further advantage of being less susceptible to loss of pinning at elevated temperatures. In addition, should such loss of pinning occur at extreme temperatures, the stable pinning structure of the current invention can revert to its initial magnetization upon cooling, without shifting of the magnetization that occurs with conventional devices. Furthermore, the invention relaxes the stringent manufacturing tolerances required by some prior art proposals.
Although the improved pinning structure of the present invention can be employed with various forms of magnetoresistive sensors or other devices, particular utility is found with a spin valve sensor that has a free layer separated from one of the pinned layers by a conductive, nonmagnetic layer. Additionally, a dual stripe sensor that reduces common mode noise can be formed around the stable pinned structure.
REFERENCES:
patent: 5465185 (1995-11-01), Heim et al.
patent: 5508867 (1996-04-01), Cain et al.
patent: 5583725 (1996-12-01), Coffey et al.
patent: 5612098 (1997-03-01), Tan et al.
patent: 5696654 (1997-12-01), Gill et al.
patent: 5701222 (1997-12-01), Gill et al.
patent: 5701223 (1997-12-01), Fontana et al.
patent: 5705973 (1998-01-01), Yuan
patent: 5717550 (1998-02-01), Nepala et al.
patent: 5742162 (1998-04-01), Nepela
Lai Chih-Huang
Min Tai
Tong Hua-Ching
Zhu Jian-Gang
Heinz A. J.
Lauer Mark
Read-Rite Corporation
LandOfFree
Spin valve sensor with antiferromagnetic and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spin valve sensor with antiferromagnetic and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spin valve sensor with antiferromagnetic and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2566853