The second generation spintronic materials and devices

In this seminar, we will first present the growth, interface magnetism and magnetotransport of several important magnetic-semiconductor hybrid spintronic structures, in particular, with half metallic magnetic oxides and Heusler alloys. The hybrid spintronic structures integrating half-metallic magnetic oxides and Heusler alloys are particularly exciting for the second generation spintronics as a 100% spin polarisation is expected for high efficient spin injection. We have synthesized for the first time single crystal half metallic Fe₃O₄ on GaAs, and further found a moderate Schottky barrier in this system ideal for spin-injection. The ultrathin single crystal Fe films were first grown on the GaAs substrate by MBE, and the sample was exposed to O₂ in the growth chamber, maintaining the O2 partial pressure at 5x10^-5 mbar with a leak valve. Similar to the discussion of Fe on the GaAs(100) substrate, the oxide exhibits a four-fold symmetry in the film plane, which gives rise to similar RHEED patterns with the electron beams along the [Oil] and [0-11] directions. The sharper RHEED patterns confirm a uniform Fe₃O₄ growth. Using the elementary specific XMCD technique, we have found that the reduced spin moments of the Heusler alloy films on GaAs come from the Mn rather than the Co, but the orbital moments are not reduced. In the metal based system, our XMCD study demonstrated that the Fe atoms on GaAs (100) are ferromagnetic with bulk-like spin moments down to nanometer and atomic scale. For device applications, we have fabricated a novel vertical magnetic/semiconductor spintronic device with a GaAs membrane, and a large change of MR was observed which indicates a large room temperature electric spin injection and detection in the hybrid spintronic structures.