Abstract
We investigate transport through 5–10 nm thin epitaxial GaAs(001) and (110)barriers sandwiched between polycrystalline iron films. It turns out thattunnelling is the dominant transport mechanism; this is indicated by a nonlinearI–V-characteristic, an exponential dependence of the tunnelling current on the barrier thicknessand the temperature dependence of the current. We observe a pronounced tunnellingmagnetoresistance (TMR) effect at low magnetic fields. Annealing decreases the TMReffect drastically and indicates the sensitivity of this effect to layer intermixing. At highmagnetic fields we observe a distinct negative magnetoresistance (MR) at low temperaturesand a positive MR at higher temperatures. This negative MR contribution is only observedfor ferromagnetic iron contacts and is absent if iron is replaced by copper or goldelectrodes.
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