Berlin 2015 – scientific programme
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MA: Fachverband Magnetismus
MA 49: POSTER II
MA 49.30: Poster
Thursday, March 19, 2015, 15:00–18:00, Poster A
Order-disorder transitions in Co2FeAl0.5Si0.5 probed via in-situ neutron diffraction — •Ahmad Omar1, Matthias Frontzek2, Alexey Alfonsov1,3, Bernd Büchner1,4, and Sabine Wurmehl1,4 — 1IFW Dresden, 01069, Germany — 2Paul Scherrer Institute, 5232 Villigen, Switzerland — 3Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan — 4Institut für Festkörperphysik, TU Dresden, 01062, Germany
The Co2FeAl0.5Si0.5 Heusler compound is predicted to be a half-metallic ferromagnet in the ordered L21 structure [1], and a high TMR ratio has been reported [2]. Heusler compounds are prone to anti-site disorders which strongly affect the physical properties. It is thus pertinent to understand the existential regimes of different disorders and order-disorder transitions. Here we present neutron diffraction measurements performed in-situ during annealing of powder samples. We have also measured pre-annealed powder samples at room temperature to compare the effect of annealing. We do not observe any sharp transition between the L21-B2 and B2-A2 disorders, which is in contrast to literature [3]. The transitions seem to be predominantly entropy-driven, although the TCurie and the transition temperature seem coupled. Also, zero-field NMR on powder with alternate annealing, as per neutron data, shows a higher L21 ordering. In summary, we gain an understanding of the order-disorder transitions and propose an alternate annealing for improved ordering. Ref.: [1] Fecher et al. J. Phys. D: Appl. Phys. 40 (2007) 1582-1586 [2] Tezuka et al. Appl. Phys. Lett. 94 (2009) 162504 [3] Balke et al. Appl. Phys. Lett. 90 (2007) 242503