Berlin 2015 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 49: POSTER II

MA 49.30: Poster

Donnerstag, 19. März 2015, 15:00–18:00, Poster A

Order-disorder transitions in Co₂FeAl_0.5Si_0.5 probed via in-situ neutron diffraction — •Ahmad Omar¹, Matthias Frontzek², Alexey Alfonsov^1,3, Bernd Büchner^1,4, and Sabine Wurmehl^1,4 — 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 Co₂FeAl_0.5Si_0.5 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 T_Curie 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