Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 10: Magnetic Materials

MA 10.5: Vortrag

Montag, 25. Februar 2008, 16:15–16:30, H 1028

Magnetism in Pb₃Mn₇O₁₅ — •J. C. E. Rasch^1,2, D. Cheptiakov², M. Boehm¹, J. Schefer², N. V. Volkov³, K. A. Sablina³, and G. A. Petrakovskii³ — ¹Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble, Cedex 9, France — ²Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland — ³L.V. Kirensky Institute of Physics SB RAS, Krasnoyarsk 660036, Russia

The wide variety of physical properties in perovskite manganites stimulates the study of other Mn oxide families without perovskite structure, but a mixed valence state of the Mn ions (Mn³⁺/Mn⁴⁺).The material under investigation is the quasi 2D compound Pb₃Mn₇O₁₅. Both existing models describing the crystal structure [1,2] were disproved and a new model based on the orthorhombic space group Pnma could be identified. Magnetisation measurements give evidence of strong antiferromagnetic correlations. A huge step at T=70 K indicates a 3D long range ordered state and a second smaller step at T=20 K is interpreted as reorientation of some moments due to a variation of the magnetic anisotropy with temperature. Neutron single crystal and powder diffraction measurements revealed two magnetic phases in PbO-MnO₂-Mn₂O₃ indicating the presence of different oxidation states. The disappearance of magnetic peaks at T=20 K and T=70 K coincides with the magnetisation measurement. [1] R. E. Marsh, and F. H. Herbstein, Acta Cryst. B 39, 280 (1983). [2] Y. Le Page, and L. D. Calvert, Acta Cryst. C 40, 1787 (1984).