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Schematic representation of the following: (a) heterostructure of quantum well spin modulator with ferromagnetic MnAs as spin injector. The entire heterostructure is grown by molecular beam epitaxy; (b) biasing arrangement for the measurements which are done by applying a constant current bias across the MnAs polarizer and analyzer contacts of the spin valve and varying the gate bias between the gate and polarizer terminals. The variation of magnetoresistance with is determined by measuring the difference in voltage for parallel and antiparallel magnetization of the polarizer and analyzer.
Magnetoresistance measured at 10 K in a conventional spin valve fabricated with an identical heterostructure [Fig. 1(a)], without gate bias. The channel length for the device is . The inset shows peak magnetoresistance vs bias current measured in the same device at different temperatures. The dashed lines are guides to the eye.
Measured modulation of magnetoresistance with gate bias at 10 and 20 K in an quantum well spin valve for (a) spin transport normal to direction of magnetization; and (b) spin transport parallel to direction of magnetization. The direction of magnetization is always along the direction, which is the easy axis of magnetization of type B MnAs contacts. The insets show the measured output voltage as a function of normalized for parallel and antiparallel magnetization (maximum actual gate voltage applied for this measurement is 8 V).
Measured output voltage for parallel and antiparallel magnetizations of the polarizer/analyzer, and magnetoresistance as a function of gate bias for a GaAs spin valve with a gate terminal as shown in Fig. 1(b) (maximum actual gate voltage applied for this measurement is 5 V).
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