Psi-k - Ab initio (from electronic structure) calculation of complex processes in materials

Working Group 9 - Magneto-electronics (WG9 Web pages)

Paul Kelly, U Twente, Netherlands

A new area of research in magnetism, called "Spin Electronics" or "Magnetoelectronics" started with the discovery of the "Giant Magnetoresistance" (GMR) effect in 1988. A new electronics is envisioned in which the electron transport is manipulated using not only the charge of the electron as in conventional electronics, but also using the intrinsic electron spin. Thanks in large part to the work of the European theory groups, which collaborate in this Network, the problem posed by the original GMR effect is now quite well understood. However, new effects continue to be found, even in metallic systems. Current-induced magnetization reversal ("spin transfer") was proposed on theoretical grounds but only recently observed. Understanding it requires studying spin transport in non-collinearly aligned magnetic systems. Tunneling magnetoresistance (TMR) is found in transport through magnetic tunnel junctions with amorphous or epitaxial barriers. Such functions could form the basis for a new non-volatile magnetic random access (MRAM) storage technology. Although leading industrial companies have already working MRAM prototypes and are planning market introduction in 2003/2004, the physical understanding of the effect is still in its infancy. Our ambition for the coming years is to understand the TMR effect well enough to be able to make reliable materials-specific predictions.

To form a link between conventional semiconductor-based electronics and transition metal based spin-electronics, it is necessary to find a way to inject a spin-polarized current from a ferromagnet into a semiconductor. Here reliable calculations for the ferromagnet/semiconductor interface would be very important to understand the nature of the interface states, which determine the Schottky barrier and govern the injection process. Collaboration with WG7 on semiconductors and nano-technology will clearly be important and will be undertaken. An ab-initio search for new half-metallic ferromagnetic alloys with 100% spin polarization at E_f and of their interfaces with semiconductors could be very fruitful. Ab-initio calculations could also play an important role in the search for new dilute ferromagnetic semiconductors with Curie temperatures well above room temperature and/or which can be doped n-type. This could enable an all-semiconductor spin electronics (at present the record Curie temperature stands at 110K for GaMnAs). Finally, understanding the spin dependent transmission at the Ferromagnet/Superconductor interface, i.e. the Andreev reflection,in terms of realistic bandstructures is another ambitious aim. All these problems can be addressed using standard density functional calculations for the ground state, and calculations based on the Kubo-Greenwood or Landauer-Buettiker formalism for the spin-dependent transport.

MEMBERS OF THE WORKING GROUP [12 + 8 others interested]

OTHERS INTERESTED