Magnetic Sensor Bias Field Cancels Interlayer Coupling
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Solution Overview
Problem
Magnetic sensor systems employing spin-valve magnetoresistive elements face reduced sensitivity due to interlayer coupling magnetic fields, which affect the resistance change with external magnetic field direction, and existing solutions do not effectively mitigate this issue.
Innovation Solution
A magnetic sensor system with a spin-valve magnetoresistive element and a bias field generation unit, where the bias magnetic field includes components to cancel out interlayer coupling magnetic fields and stabilize the free layer's magnetization, comprising at least one magnet with magnetization components parallel and perpendicular to the end face, applied orthogonally to the sensor element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spin-valve magnetoresistive element is used in a magnetic sensor, then the sensor can detect external magnetic fields, but the free layer receives an interlayer coupling magnetic field from the magnetization pinned layer that causes the resistance change amount to vary depending on external magnetic field direction and reduces overall resistance change
Solution Approach 1:
A nonmagnetic layer is introduced as an intermediary between the magnetization pinned layer and the free layer. This nonmagnetic layer acts as a magnetic field shield that blocks the interlayer coupling magnetic field from reaching the free layer, thereby preventing the harmful effect while maintaining the necessary magnetic detection function.
Solution Approach 2:
The harmful interlayer coupling magnetic field effect is extracted and isolated by placing a nonmagnetic layer between the magnetization pinned layer and the free layer. This separation removes the unwanted magnetic interaction while preserving the functional magnetic field detection capability.
2Object-affected harmful factors
If the interlayer coupling magnetic field is reduced to zero, then the harmful effect is eliminated, but the output waveform of the magnetic sensor becomes unstable
Solution Approach 1:
The nonmagnetic layer is selectively positioned only between the magnetization pinned layer and the free layer, providing localized magnetic field blocking exactly where needed. This localized intervention eliminates the harmful interlayer coupling effect while preserving the overall stability of the magnetoresistive element structure and output waveform.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces the effect of interlayer coupling magnetic fields, stabilizes the magnetization direction, and enhances the sensitivity of the magnetic sensor system by ensuring consistent resistance changes with external magnetic field variations.
Implementation Method 1
the free layer receives an interlayer coupling magnetic field in a direction parallel to the first direction resulting from the magnetization pinned layer
Implementation Method 2
The bias magnetic field includes a first magnetic field component in a direction opposite to the direction of the interlayer coupling magnetic field
Implementation Method 3
a free layer having a magnetization whose direction and magnitude vary depending on an external magnetic field
Data Source
AI summary
A magnetic sensor includes an MR element and a pair of magnets. The MR element includes a magnetization pinned layer having a magnetization pinned in a direction parallel to an X direction, a free layer having a magnetization that varies depending on an X-direction component of an external magnetic field, and a nonmagnetic layer interposed between the magnetization pinned layer and the free layer. The magnetization pinned layer, the nonmagnetic layer and the free layer are stacked to be adjacent in a Y direction. The free layer receives an interlayer coupling magnetic field in a direction parallel to the X direction resulting from the magnetization pinned layer. The pair of magnets applies a bias magnetic field to the free layer. The bias magnetic field includes a first component in a direction opposite to that of the interlayer coupling magnetic field and a second component in a Z direction.