Magnetic domain control for an embedded contact sensor for a magnetic recording head

A head for magnetic data recording that includes an embedded contact sensor. The embedded contact sensor detects head disk contact by detecting changes in temperature as a result of contact between the head and the disk. The embedded contact sensor includes a thermoresistive layer and a structure for pinning the magnetic domains of the thermoresistive layer. This pinning of the magnetic domains prevents the thermoresistive layer from changing resistance in response to magnetic fields (rather than temperature) so as to avoid unwanted signal noise as a result of a magnetic signal from the magnetic media.

FIELD OF THE INVENTION

The present invention relates to magnetic data recording and more particularly to a magnetic read head having an embedded contact sensor with magnetic domain stabilization for improved detection of head disk contact.

BACKGROUND OF THE INVENTION

The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.

The write head includes at least one coil, a write pole and one or more return poles. When a current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic disk, thereby recording a bit of data. The write field, then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.

A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor or a Tunnel Junction Magnetoresisive (TMR) sensor can be employed to read a magnetic signal from the magnetic media. The sensor includes a nonmagnetic conductive layer (if the sensor is a GMR sensor) or a thin nonmagnetic, electrically insulating barrier layer (if the sensor is a TMR sensor) sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. Magnetic shields are positioned above and below the sensor stack and can also serve as first and second electrical leads so that the electrical current travels perpendicularly to the plane of the free layer, spacer layer and pinned layer (current perpendicular to the plane (CPP) mode of operation). The magnetization direction of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetization direction of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.

When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering of the conduction electrons is minimized and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. In a read mode the resistance of the spin valve sensor changes about linearly with the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.

In order to maximize the performance of a magnetic data recording system it is important to minimize the magnetic spacing between the read and write heads and the magnetic medium. However, as this magnetic spacing decreases, the probability of head disk contact during operation also increases. Contact between the head and the magnetic medium (e.g. disk) can have catastrophic effects, including damage to the magnetic sensor and damage to the magnetic media resulting in loss of data and failure of the magnetic recording system. One way to monitor the spacing between the head and the disk is to incorporate an embedded contact sensor in order to determine when head disk contact has occurred or is likely to occur. However, such embedded sensor suffer from extreme signal noise, such as from magnetic signals from the magnetic media that can prevent the embedded contact sensor from accurately determining whether head disk contact has occurred or is imminent.

SUMMARY OF THE INVENTION

The present invention provides an embedded contact sensor that includes a thermoresistive layer; and a structure for pinning magnetic domains in the thermoresistive layer.

The structure for pinning the magnetic domains of the thermoresistive layer can be a hard magnetic structure formed at the sides of the thermoresistive layer or can be a layer of antiferromagnetic material that is exchange coupled with the thermoresistive layer.

The domain pinning structure of the present invention advantageously prevents the embedded contact sensor from inadvertently detecting magnetic fields through a magnetoresistive effect such as an anisotropic magnetoresistive (AMR) effect. This greatly reduces signal noise and prevents inadvertently mistaking a magnetic signal for a head disk contact.

These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

During operation of the disk storage system, the rotation of the magnetic disk112generates an air bearing between the slider113and the disk surface122which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension115and supports slider113off and slightly above the disk surface by a small, substantially constant spacing during normal operation.

With reference toFIG. 2, the orientation of the magnetic head121in a slider113can be seen in more detail.FIG. 2is an ABS view of the slider113, and as can be seen the magnetic head including an inductive write element202and a read element204, is located at a trailing edge of the slider. The magnetic head121also includes an embedded contact sensor206, which will be described in greater detail herein below. The embedded contact sensor206has an electrical resistance that changes in response to heat generated as a result of head disk contact. This change in electrical resistance can be detected by processing circuitry (not shown inFIG. 2). The above description of a typical magnetic disk storage system and the accompanying illustration ofFIG. 1are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders.

The magnetic write head202is an inductive write head that includes a magnetic write pole208and a magnetic return pole210. A write coil (not shown inFIG. 2) produces a magnetic field that causes a magnetic flux to flow through the write pole208that generates a magnetic write field that emits from the write pole208toward the magnetic medium112(FIG. 1). This magnetic write field is sufficiently strong to write a magnetic bit to the magnetic media. The magnetic flux returns the return pole210where it is sufficiently spread out and weak that it does not erase the previously recorded magnetic bit.

The read head204includes a magnetoresistive sensor212such as a giant magnetoresistive sensor (GMR) or a tunnel magnetoresistive sensor (TMR). The magnetoresistive sensor212is sandwiched between first and second magnetic shield214,216, which can be constructed of an electrically conductive magnetic material so that they can function as electrically conductive leads as well as magnetic shields.

With reference now toFIG. 3, an embedded contact sensor206according to an embodiment of the invention will be described. The embedded contact sensor206includes a thermoresistive layer304that is constructed of a material that has an electrical resistance that changes in response to a change in temperature. This layer304can be formed on a substrate302that can be a non-magnetic, electrically insulating material such as alumina. The thermoresistive layer304detects the heat generated by contact between the head and the disk as a change in resistance value. Contact leads306,308can be provided in order to supply a voltage across the thermoresistive layer304and these leads306,308can be connected with processing circuitry316that can detect the change in resistance across the layer304as a result of a head/disk contact induced rise in temperature. Unlike a GMR or TMR magnetoresistive sensor, which can have include a magnetic pinned layer, a magnetic free layer, a non-magnetic layer sandwiched between the free and pinned as well as other layers arranged specifically to produce a change in resistance in response to a magnetic field, the layer304is preferably a simple, single layer of material that is specifically chosen to produce a change in electrical resistance in response to a change in temperature.

The temperature coefficient of this layer304determines the sensitivity of the sensor206during contact. Generally, a metal material having a large temperature coefficient such as nickel (6.7*10−3/° C.), iron (6.6*10−3/° C.), or cobalt (6*10−3/° C.) is used. Therefore, the layer304can be constructed of Ni, Co, Fe or a combination of these materials. However, in addition to having thermoresistive properties, these materials also have magnetoresistive properties. This can be based on the anisotropic magnetoresistive (AMR) effect. This means that the resistance of the layer304changes in response to a magnetic field. When the contact sensor206is close to the magnetic media, the magnetic signal from the magnetic media results in a change in resistance in the layer304. Ideally, the embedded contact sensor should only produce a signal in response to contact with the disk/media. This magnetic response is the result of magnetic domain movement in the layer304. Therefore, the resistance change resulting from the magnetic field from the media produces noise in the signal from the contact sensor602and can lead to a false positive head/disk contact indication. In addition, transitions arise in the resistance of layer304by the motion of the magnetic domain caused by changes in stress or heat during contact. These changes become noise components in the contact detection between the magnetic head and the magnetic disk and become a source of incorrect contact indication.

The present invention overcomes this problem by pinning the magnetic domain of the layer304to prevent heat, stress or external magnetic fields from causing changes in the magnetic domain of the layer304, which would result in an inadvertent change in resistance of the layer304.

In the embodiment ofFIG. 3, in order to pin the magnetic domains of the layer304, hard magnets310,312are provided at either side of the thermoresistive layer304. These layers can be a high magnetic coercivity, magnetic material that preferably has a desired magnetic anisotropy, such as a shape induced magnetic anisotropy. Suitable materials for the layers310,312could be, for example, CoPt or CoPtCr. In addition, certain seed layers (not shown) could be provided to induce a desired grain structure and desired magnetic properties in the layers310,312. This allows the layers310,312to produce a magnetic pinning field314that pins the magnetic domain of the thermoresistive layer304in a direction parallel with the layer304and parallel with the ABS as indicated by arrows314. With the magnetic domains of the thermoresistive layer304pinned in this manner, the resistance of the layer304will only respond to head disk contact induced heat spikes and not to external magnetic fields, such as those from the magnetic media.

FIG. 4shows an embedded contact sensor402according to another embodiment of the invention. As with the previously described embodiment, the sensor402has a thermoresistive layer304that can be constructed of a material such as Ni, Fe, Co or a combination of these materials. The sensor402also has leads306,308and processing circuitry316for detecting a change in resistance of the layer304as a result of a head/disk contact induced heat spike.

However in the sensor402, rather than using hard magnetic layers at either side of the layer304(e.g. in series), the sensor402employs a layer of antiferromagnetic material404to pin the magnetic domains of the layer304. The layer404can be constructed of an antiferromagnetic material such as IrMn, PtMn etc. and can be formed upon a substrate302such as alumina. One or more seed layers (not shown) can also be provided at the bottom of the layer404to insure desired magnetic properties in the layer404.

The layer of antiferromagnetic material404is formed directly beneath the thermoresistive layer304and is exchange coupled with the thermoresistive layer304. An antiferromagnetic material such as IrMn or PtMn does not have a magnetic moment in and of itself. However, when it is exchange coupled with a magnetic material (such as the layer304) it very strongly pins the magnetization of the magnetic layer to which it is exchange coupled. Therefore, this layer404can strongly pin the magnetic domains of the thermoresistive layer304. This very effectively prevents the resistance of the layer304from changing in response to a magnetic field such as that from the magnetic media.