Regensburg 2016 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 17: Poster Session I

MA 17.64: Poster

Dienstag, 8. März 2016, 09:30–12:30, Poster B1

Understanding the ordering phenomena in Co₂FeAl_0.5Si_0.5 through in situ neutron diffraction — •Ahmad Omar¹, Matthias Frontzek², Alexey Alfonsov¹, Bernd Büchner^1,3, and Sabine Wurmehl^1,3 — ¹IFW Dresden, 01069, Germany — ²Paul Scherrer Institute, 5232 Villigen, Switzerland — ³Institut 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 but it is difficult to obtain a pure L2₁ order due to anti-site disorder. Hence, 100% spin polarization has not been observed in general. Therefore, it is important to understand the ordering phenomena with temperature in the material so as to optimize the ordering post-synthesis. We present in situ neutron diffraction measurements performed during high temperature annealing of powder samples along with powder neutron diffraction at room temperature on pre-annealed polycrystalline samples in order to compare the effect of various annealing procedures. We show that the annealing procedures commonly followed in literature do not offer significantly large improvement in the L2₁ order. A sharp L2₁-B2 ordering transition is not observed, in contrast to what is commonly understood. We also discuss the ordering phenomena in the light of existence and evolution of antiphase domains and domain boundaries though detailed line profile analysis of the neutron diffraction data. Based on our understanding, we have been able to optimize the annealing procedure. A higher L2₁ ordering, as compared to conventional annealing, has been obtained which was confirmed using zero-field NMR measurements.