Dresden 2011 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 41: Topical Session Diffussionless Transformations II
MM 41.5: Talk
Thursday, March 17, 2011, 17:15–17:30, IFW D
Competing structural ordering tendencies in new high-TC ferromagnetic Fe-Co-based Heusler alloys from ab initio investigations — •Antje Dannenberg1, Markus Gruner1, Manfred Wuttig2, and Peter Entel1 — 1Faculty of Physics, University of Duisburg-Essen, 47048 Duisburg, Germany — 2Department of Materials Science and Engineering,University of Maryland, College Park, MD 20742, USA
Fe-Co-based Heuslers are candidates for new ferromagnetic shape memory alloys (FSMA) as they promise higher operation temperatures compared with prototype Ni2MnGa. Of interest are also the corresponding binary systems FeZn and Fe3Ga which show a huge magnetostriction. We present results of ab initio and Monte Carlo calculations regarding structural, magnetic, and electronic properties of Fe2CoGa1-xZnx alloys in conventional X2YZ and inverse (XY)XZ Heusler structures. All systems exhibit high Curie temperatures TC. The preference of the cubic inverse structures is believed to originate from the bcc-like environment of two inequivalent Fe atoms and their strong hybridization with the Co- states. Weakening the Co-Fe hybridization by substitution of Ga by Zn reduces this preference and leads to higher TC but simultaneously reduces the miscibility. Despite the strong spin-dependent Fe-Co hybridization we find a localized character of the spin moments. Extraordinary Z-elements like Cu, Ag, and Au or further enhancement of the Zn content induces a martensitic instability also in the inverse structures. Thus, we conclude that it is possible to find new FSMA with rather high Curie temperatures.