FOR 1464: ASPIMATT: Advanced Spintronic Materials and Transport Phenomena
Physics
Final Report Abstract
Aim of the Research Unit “Advanced spintronic materials and transport phenomena (ASPIMATT)” was the development of materials and devices for a future spintronics with the potential to complement and succeed conventional CMOS. The specific approach lies on the development and characterization of new spintronic materials for applications at room temperature and the study of new spin transport phenomena, in particular lateral spin current phenomena. The research subject was in the field of nanoelectronics, specifically in the research area “Nanospintronics and related materials and structures”. Based on Mn3Ga, further new materials were developed that are for example the Heusler type compounds: Mn3-xGa, Mn3-xCoxGa, Mn2RhSn, or Mn2-xPtxGa. With Mn2CoAl, the first spingapless semiconductor was experimentally verified. The record magnetoresistance (MR) ratio of 74% at room temperature (RT) in CPP-GMR devices being achieved with Heusler compound electrodes by the ASPIMATT team attracted already the interest of the hard disc industry. The highest tunneling magnetoresistance (TMR) ratio (2610% at LT, 429% at RT) was achieved in a magnetic tunnel junction (MTJ) with Mn rich Heusler electrodes. The requirements for STT-RAM, low damping with low magnetization and high spin polarization are found in the new class of manganese rich Heusler compounds. ASPIMATT discovered the unique properties of bulk Mn3Ga and thin films and related systems to be used for STT-RAM and STT Oscillators. In addition it was shown that high frequency oscillation can be realized. Spin precession with frequencies up to 280 GHz was observed in Mn3-xGa alloy films with a high perpendicular magnetic anisotropy. The damping constant, characterizing macroscopic spin relaxation and being a key factor in spin-transfer-torque systems, is not larger than 0.008. In the area of lateral spin transport the CPP-GMR with continuous Co75Fe25 free layer prepared on a coplanar wave guide with low microwave transmission loss for BLS measurement was a further high light. Spin torque oscillation was observed electrically without harmonic signal. Spin injection into semiconductor (GaAs and Si) was observed even at RT. The results are published in detail in overall more than 200 papers in refereed journals.
