Dresden 2011 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 63: Poster II (Surface Magnetism/ Magnetic Imaging/ Topological Insulators/ Spin Structures and Magnetic Phase Transitions/ Graphene/ Magnetic Thin Films/ Magnetic Semiconductors/ Magnetic Half-metals and Oxides/ Spin-dependent Transport/ Spin Excitations and Spin Torque/ Spin Injection and Spin Currents in Heterostructures/ Spintronics/ Magnetic Storage and Applications)
MA 63.55: Poster
Freitag, 18. März 2011, 11:00–14:00, P2
Investigations of the ordering in Co2Mn(Si,Ge) and Co2FeSi via transport, magnetization, XRD and Mößbauer measurements — •Britta Willenberg1, Dirk Schulze Grachtrup1, Jochen Litterst1, Stefan Süllow1, Jens Röder2, and Dirk Menzel1 — 1Institut für Pysik der Kondensierten Materie, TU Braunschweig, Germany — 2Physikalische und Theoretische Chemie, TU Braunschweig, Germany
Heusler alloys like Co2MnSi, Co2MnGe and Co2FeSi have attracted interest, because some theoretical works predicted half-metallicity with 100 % spin polarization. So far, this high value has not been observed experimentally. Some calculations indicate that the lack of total spin polarization should be due to structural defects, which destroy the half-metallicity. We have investigated the effect of annealing on the quality of these compounds via transport, magnetization, XRD and Mößbauer measurements. Thermal annealing of Co2MnSi and Co2MnGe leads to an increase of the residual resistivity ratio. Furthermore, powder x-ray measurements on Co2MnSi showed that a second phase occurs in the annealed sample due to a phase segregation during annealing. In contrast to this behavior the residual resistivity ratio for Co2FeSi decreases during annealing. Moreover, by means of Mößbauer studies we found out that the disorder between some atomic sites increased during annealing and additionally a second phase arises. Thus, thermal annealing of this compound degrades the quality of the crystal.