The present invention is a magnetoresistive (MR) sensor. More specifically, the present invention is an MR sensor having a permanent magnet stabilization layer with a magnetization vector at 45.degree. with respect to an air bearing surface of the sensor, and vertical current contacts
MR sensors are used to detect magnetic flux levels stored on magnetic media. In an MR sensor, the resistance of the sensor varies with the magnitude of the flux passing through the sensor. Typically, a constant current is passed through the sensor and the magnitude of the flux passing through the sensor is represented by a change in the voltage across the sensor, which of course is a function of the resistance of the sensor Likewise, a constant voltage source can be applied to the MR sensor, in which case the magnetic flux magnitude is represented by a change in the current through the sensor.
In an MR sensor, maximum sensitivity is achieved when a static magnetization vector is applied at 45.degree. with respect to the direction of current flow through the MR sensor. This relationship exists because the output voltage of the MR sensor for any given input current is proportional to COS.sup.2.theta., where .sup..theta. is the angle between the static magnetization vector and the current vector. At 45.degree., this function provides maximum equal and opposite changes in output for corresponding equal and opposite deviations in magnetic flux.
In one typical configuration, referred to as the canted current configuration, the magnetization vector lies along a line between the first and second contacts such that the current flows through the magnetoresistive material at 45.degree. with respect to the line. To achieve this, the contacts are canted, or slanted, across the magnetoresistive material at a 45.degree. angle with respect to the line. In addition, the resistance of the contacts is significantly less than the resistance of the magnetoresistive material.
In the canted current configuration, the current flows out of the first canted contact perpendicular to the boundary between the first contact and the magnetoresistive layer. The current then flows across the magnetoresistive layer at the desired 45.degree. angle and encounters the second contact perpendicular to the boundary between the second contact and the magnetoresistive layer, which again is 45.degree. with respect to the line connecting the first and second contacts. To enhance the stability of the device, permanent magnet material may be positioned proximate the contacts such that the permanent magnet material provides a magnetic field H in the magnetoresistive layer along a line between the contacts. In addition, if Permalloy is formed into a long narrow strip, the magnetization vector M of the Permalloy will naturally point along the long axis of the strip.
One limitation of the canted current configuration is that the width of the detection region of the sensor is limited by the height of the sensor. For example, assume that the current is flowing in a sensor from right to left, and the right contact is canted at 45.degree., with the lower portion of the right contact more to the left than the upper portion. In this configuration, the current will tend to flow from the bottom of the magnetoresistive material to the top of the material. Accordingly, at 45.degree. the maximum width of the detection region equals .sqroot.2 times the magnetoresistive layer height.
Another problem associated with canted contact MR sensors is that the read sensitivity window shifts with respect to the integral write gap of the write element as the air bearing surface of the transducer is lapped. This makes it more difficult to control the read-to-write alignment of a transducer having a canted contact MR sensor and a separate write element.