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MA: Fachverband Magnetismus

MA 16: Poster I

MA 16.13: Poster

Dienstag, 12. März 2013, 10:30–13:30, Poster D

Understanding the phase sequence of Fe-Pd alloys from first principles — •Markus Ernst Gruner¹, Sandra Kauffmann-Weiß², Sven Hamann³, Peter Entel¹, Sebastian Fähler², and Alfred Ludwig³ — ¹Faculty of Physics and CeNIDE, University of Duisburg-Essen, 47048 Duisburg — ²IFW Dresden, P.O. Box 270116, 01171 Dresden — ³Institute of Materials, Ruhr-Universität Bochum, 44801 Bochum

Just as the prototypical Ni-Mn-Ga Heusler system also the disordered face centered Fe₇₀Pd₃₀ alloy shows large magnetic field induced strains in a slightly tetragonal fct martensite. Recent experiments achieved epitaxial growth of Fe₇₀Pd₃₀ thin films with c/a = 1.09, thus extending the classical Bain path beyond the fcc end [PRL 107, 206105 (2011)]. The combination of XRD spectroscopy and DFT modelling reveals that this process is related to an alternative relaxation mechanism, which leads to a nanotwinned pattern constructed from fct building blocks. The extremely low formation energy of the fct twins results in a finely twinned superstructure in the simulation cell along [110], which corresponds to the experimentally observed soft transversal acoustic phonon in this direction. This is also a central feature of the Ni-Mn-Ga magnetic shape-memory Heusler compound and allows us to interpret the fct phase analogously as a metastable adaptive martensite, where the increasing twin defect energy at larger distortions prevents the relaxation to the bcc ground state. The close interrelation between electronic and structural properties can be exploited to tailor the phase sequence in magnetic shape-memory ternary alloys.