We have fabricated fully epitaxial single-crystal MnAs/AlAs/MnAs magnetic tunnel junctions (MTJs) grown by molecular-beam epitaxy on vicinal GaAs(111)B substrates. After the bottom MnAs layer was grown at 250 °C, the successive AlAs tunnel barrier and the top MnAs layer were grown at a lower temperature of 200 °C in order to suppress the surface segregation of Mn atoms. High-resolution transmission electron microscopy revealed that a monocrystalline MnAs/AlAs/MnAs trilayer heterostructure with atomically flat and chemically abrupt interfaces was realized. Tunneling magnetoresistance (TMR) was clearly observed in fully epitaxal MTJs made up of this trilayer heterostructure. The TMR ratio was 1.4% at 10 K and it decreased with increasing the bias voltage and with increasing temperature, but the TMR effect still remained at room temperature.
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Sugahara et al. (2002) studied this question.
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