Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 32: Postersession II: Spinstruct./Phase Trans. (1-10); Spinelectronics (11-15); Thin Films (16 - 36); Particles/Clusters (37-45); Multiferroics (46-54); Spindynamics/Spin Torque (55 - 76); Post Deadlines (77-79)

MA 32.2: Poster

Freitag, 29. Februar 2008, 11:15–14:00, Poster E

Magnetic properties of the (Co_xMn_1−x)₄Nb₂O₉ solid solution series. — •Björn Schwarz¹, Daniel Kraft², Ralf Theissmann³, and Helmut Ehrenberg¹ — ¹Institute for Complex Materials, IFW Dresden, Helmholtzstrasse 20, D-01069 Dresden, Germany — ²Institute for Materials Science, Darmstadt University of Technology, Petersenstrasse 23, D-64287 Darmstadt, Germany — ³Institute for Nano Structures and Technology (NST), University of Duisburg-Essen, Bismarckstr. 81, D-47057 Duisburg, Germany

α-Fe₂O₃ (Hematite) is an antiferromagnetic material below the Morin transition at 260 K, and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Néel temperature at 948 K, above which it is paramagnetic. (Co,Mn)₄Nb₂O₉ crystallizes isostructural to α-Fe₂O₃ and the end members order collinear antiferromagentically, whereas the results of magnetization measurements (powder samples and single crystals) and powder neutron diffraction experiments for samples of the solid solution series indicate the realization of weak ferromagnetism, too. A Morin transition induced by a change in cation composition in this system would have presented a qualitatively new approach for understanding the fundamentals of the Morin-transition. Comparative experiments performed on samples of the (Co,Mn)₄Nb₂O₉ solid solution series that were prepared by arc melting instead of subsolidus reaction reveal, however, that the experiments performed on samples prepared by the latter method, even on single crystals, were decisively affected by additional (Co,Mn)₃O₄ phases possessing complex magnetic properties.