Magnetoresistive linear displacement sensor, angular displacement sensor, and variable resistor using a moving domain wall

A sensor for measuring the displacement between a first workpiece and a second workpiece, comprising:

• a magnetoresistant strip fixed to said first workpiece, comprising a plurality of hard ferromagnetic or antiferromagnetic layers alternating with a plurality of magnetic layers comprising a softer magnetic material, wherein each of said ferromagnetic or antiferromagnetic layers and said layers comprising said softer magentic material contact with and are separated by nonmagnetic conductive layers interposed between said magnetic layers, for preventing essentially all exchange coupling between said magnetic layers,
• means for inducing domain walls, at measurand positions, between regions of magnetic fields in said softer magnetic layers, wherein said magnetic fields are not aligned with each other, wherein said inducing means is fixed to said second workpiece;
• and
• means for measuring electrical resistance between points on said magnetoresistant strip, thereby measuring said positions of said domain walls, thereby measuring the position of said second workpiece relative to said first workpiece.

A variable resistor, comprising:

• a magnetoresistant strip, comprising at least one laminate structure, wherein said laminate structure comprises a first hard ferromagnetic or antiferromagnetically-pinned layer having a fixed magnetic state, a second magnetic layer over said first magnetic layer, and a nonmagnetic conductive layer interposed between and contacting said magnetic layers, wherein said second magnetic layer comprises a softer magnetic material than said first magnetic layer;
• means for inducing a domain wall, at a selected point, between regions of nonaligned magnetic field in said second magnetic layer, thereby setting the resistance across said magnetoresistant strip to a selected value;
• and
• means for moving said means for inducing said domain wall to a selected position, thereby changing the resistance across said magnetoresistant strip.

A sensor for measuring the relative movement in a selected direction between a first workpiece and a second workpiece, comprising:

• a giant magnetoresistant strip fixed to said first workpiece, wherein said magnetoresistant strip comprises at least one laminate structure, wherein said laminate structure comprises a first hard ferromagnetic or antiferromagnetically-pinned layer, a second magnetic layer over said first hard ferromagnetic or antiferromagnetic layer, wherein said second magnetic layer comprises a softer magnetic material than said first layer, and a conductive layer interposed between and contacting said first and second layers, for preventing essentially all exchange coupling between said first and second layers;
• inducing means for inducing a domain wall, between regions of magnetic fields in said second magnetic layer, wherein said magnetic fields are not aligned with each other, wherein said inducing means is fixed to said second workpiece;
• and
• measuring means for measuring changes in electrical resistance between points on said magnetoresistant strip, thereby measuring the movement of said domain wall in said selected direction, thereby measuring the movement of said second workpiece relative to said first workpiece in said selected direction.