University of Delaware - College of Engineering



Spintronic Sensors and Microwave Phase Detection

James Kolodzey

This project addresses the application of magneto-resistive sensors to detect biochemicals, including DNA and proteins. The operating principle is that magnetic particles of nanometer size are prepared as markers that tag biomolecule targets by chemical binding. A complementary probe biochemical, which specifically bonds to the sought target, is anchored to the surface of the magneto-sensors by chemical surface treatment. The magneto-sensor is placed in close proximity to a test sample of biochemicals, by micropipette. If the target molecule matches its complementary probe anchored to the sensor surface, the molecules will bind, along with their nanomagnet tags, and stay fixed to the sensor surface without being washed away. If the magneto-resistance sensor shows a change in resistance by the fringing field of the nanomagnet, the presence of that particular target is indicated. If the probe and target do not match, the target molecules get washed away with their nano-tags, and there is no change in magnetoresistance. The magneto-resistive sensors have been shown to detect a single magnetic particle of micron-size.

A microwave magnetic field can precess the free magnetic layer in spin valve devices and magnetic tunnel junctions. Consequently, the magnetoresistance changes, leading to an average resistance change with respect to the initial state (parallel or antiparallel). A dc current applied through the device picks up the resistance change and converts it into an ac voltage signal which can be detected using a lock-in technique. We found that the ac voltage signal is related to the microwave power.

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