Ballistic Spin Transport in Four-Terminal NiFe/In_<0.75>Ga_<0.25>As Structure : Semiconductors

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Spin-injection experiments in NiFe/two-dimensional electron gas (2DEG)/NiFe four-terminal devices are described. The 2DEG was confined at a modulation-doped In_<0.75>Ga_<0.25>As/In_<0.75>Al_<0.25>As heterojunction interface. NiFe source-drain electrodes were located 〜 1 /μm apart and two voltage probes were fabricated between them. The separation between the NiFe electrodes was thus almost less than both the mean free path (〜2 μm) and the spin-diffusion length (> 1 μm) of the 2DEG. In nonlocal four-terminal measurements, where a constant current (i) was sent through one NiFe to one ohmic electrode, the two-terminal magnetoresistance (R_<2t> = V_<2t>/i) exhibited a spin-valve-like effect, while R_<4t> = V_<4t>/i showed a resistance hysteresis. The amplitude of the latter amounted to almost 12% of the R_<4t> (B = 0) at 1.5 K, the extent of which was one order of magnitude larger than those so far reported. These results suggest the importance of a quasi-ballistic as well as a spin-coherent coupling between the two NiFe electrodes, which may crucial in the future operation of spin field-effect transistors (FETs).
社団法人応用物理学会の論文
2001-10-15