FOR 559:  New Materials with High Spin Polarisation

• Subject Area: Physics
• Term: from 2004 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5471292

The objective of the Research Unit is the development and investigation of new Heusler compounds and double perovskites with high spin polarisation at room temperature. On one hand, many Heusler compounds and double perovskites are predicted to be half-metallic ferromagnets, on the other hand there exists no tunneling magneto resistive device (TMR) exhibiting the magneto resistance expected from theory, up to now. First promising results were found by groups involved in the Research Unit. Based on a chemical model, materials with a potential for high magneto resistance were selected and synthesised. Attention was attracted by the prediction and discovery of a very high magneto resistance of the Fe doped Heusler compound Co2CrAl. A high value was reached at room temperature in granular pressed powder pellets. These results were confirmed by measurements of M. Coey's group at the Trinity-College in Dublin. Recently, a single-sided TMR junction based on Co2Cr0.6Fe0.4Al was build by a Japanese group. It shows an effect of 19% at room temperature. This does not correspond to 100% spin polarisation, but was the first TMR device based on a Heusler compound. Double perovskites with molybdenum or rhenium exhibit high magneto resistance already at room temperature, too. This makes them promising candidates for spintronics. The expertise of the Research Unit is on the first place the possibility to synthesise the rhenates, being otherwise hardly accessible. These compounds exhibit some similar behaviour like the Heusler compounds.
The improvement of the fundamental physical knowledge about such materials is the scientific objective of the Research Unit, in particular, the understanding of their magneto resistance based on the peculiarities of their electronic structure. Another main goal is the investigation of surface and interface effects in order to gain knowledge about how to improve materials and devices.
The success in the development of material specific models is guaranteed by the collaboration of groups from physics and chemistry.

• DFG Programme: Research Units

Projects

• Characterization of the surface electronic, magnetic and dynamical properties of new materials with high spin polarization (Applicant Aeschlimann, Martin )
• Double perovskites with high spin polarization (Applicant Tremel, Wolfgang )
• Investigation of the electronic and magnetic structure of materials with high spin polarization by means of experimental and theoretical methods (Applicant Felser, Claudia )
• Magnetic interface properties of new materials with high spin polarization (Applicant Elmers, Hans-Joachim )
• Magneto-optical investigations and ion beam-induced modification of materials with high spin polarization (Applicant Hillebrands, Burkard )
• Mikroskopische Theorie der Doppelperowskite: LDA+DMFT mit Auswertung durch QMC (Applicant Blümer, Nils Michael )
• Mößbauer-Spektroskopie zur Charakterisierung neuer Materialien mit hoher Spinpolarisation: Hochtemperatur- und CEMS-Untersuchungen (Applicant Ksenofontov, Vadim )
• Preparation and investigation of interfaces of Heusler thin films (Applicant Jourdan, Martin )
• Synthesis of new materials with high spin polarization and high Curie temperatures (Applicant Felser, Claudia )
• Thin films of new materials with high spin polarization (Applicant Jakob, Gerhard )
• Zentralprojekt (Applicant Felser, Claudia )

• Spokesperson: Professorin Dr. Claudia Felser
• Deputy: Professor Dr. Burkard Hillebrands