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 32.9: Poster

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

Crystal structure and magnetic fluctuations in La_1−xA _xCoO₃ (A = Ca, Sr, Ba) — •Thomas Finger¹, Marco Reuther¹, Daniel Senff¹, Matthias Cwik¹, Thomas Lorenz¹, Markus Braden¹, Klaudia Hradil², Anatoliy Senychyn³, and Yvan Sidis⁴ — ¹II. Physikalisches Institut, Universität zu Köln — ²Georg-August Universität Göttingen / FRM2 Munich — ³Technische Universität Darmstadt / FRM2 Munich — ⁴LLB, Saclay

The phase diagram of perovskite cobaltites is closely related to those of the CMR-manganites as they both show ferromagnetism and metallic behaviour at intermediate doping. We have studied the crystal structure of the series with Ca and Ba doping and will discuss the corresponding phase diagrams. Furthermore, magnetic excitations were studied by inelastic neutron scattering for A = Sr at different doping levels. We report on the magnetic correlations in the ferromagnetic and in the spin-glass phase and present the magnon dispersions which are remarkably different. In the metallic compound we find a very steep ferromagnetic dispersion, with a stiffness constant twice higher than that in La_0.7Sr_0.3MnO₃ and a small anisotropy gap, without any evidence for a splitting of the magnon branches. In contrast the magnetic excitations in the spin-glass phase exhibit a sizeable spin gap and a much more complex low-energy magnetic excitation spectrum. This is the first clear evidence that the spin-glass phase cannot be considered as a short-range analogue of the ferromagnetic phase.