Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 10: Spinelectronics/Spininjection in Heterostructures
MA 10.7: Talk
Monday, March 26, 2007, 16:45–17:00, H23
First-principles prediction of high Curie temperature for ferromagnetic bcc-Co and its relation to Co/MgO/Co magnetic tunnel junctions — •Phivos Mavropoulos, Marjana Ležaić, and Stefan Blügel — IFF, Forschungszentrum Jülich, Jülich, Germany
We determine from first principles the Curie temperature of bulk Co in the ground state hcp phase and the metastable fcc and bcc phases. For fcc-Co we found a Curie temperature of TC(fcc-Co)=1280 K, in reasonable agreement with experimental results. For bcc-Co, a Curie temperature of TC(bcc-Co)=1400 K is predicted. This suggests that bcc-Co/MgO/bcc-Co tunnel junctions offer high tunneling magnetoresistance ratios even at elevated temperatures, giving them an advantage over Fe/MgO/Fe junctions. TC(bcc-Co) appears robust under tetragonalization upon epitaxial growth on MgO, in contrast to Fe for which TC(bcc-Fe) is found to drop by more than 20% (from 970 K to 750 K) upon such a tetragonalization. We find that FeCo alloys have an even higher TC, as high as 1660 K for ordered FeCo. We discuss the origin of these effects in terms of the electronic structure and densities of states. The Curie temperatures are calculated by mapping ab initio results to a Heisenberg model, which is solved by a Monte Carlo method.