Giant-magnetoresistance in hybrid semiconductor/ferromagnetic nanodevices
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This thesis describes an experimental study a new class of hybrid ferromagnetic/semiconductor device that demonstrates a nonvolatile memory function, and which may permit large-scale integration of logic and memory on the same chip. In our prototype device, a narrow quantum wire etched in a high mobility GaAs/AlGaAs heterostructure acts as the channel, and is gated by a ferromagnetic strip. This strip generates spatially inhomogeneous magnetic fields that can modify the conductance, in combination with the usual electrostatic action of the gate. In the tunneling regime, the magneto-resistance of this device exhibits a giant, hysteretic modulation (600% at liquid helium temperature and 20% at 150 K). A theoretical model that considers wave-vector dependent transmission through the barrier is able to account for our observations. In related work, we also explore the interplay of semi-classical and quantum transport phenomena for determining the transmission properties of pure magnetic barriers. Our results demonstrate the existence of two different regimes of behavior in which these respective phenomena are dominant. Overall, our results reveal the important considerations for successful implementation of hybrid devices.