Regensburg 2007 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 14: Spin Systems and Itinerant Magnets
TT 14.12: Talk
Tuesday, March 27, 2007, 17:15–17:30, H19
Magnetic properties of the layered cobaltates La2−xSrxCoO4 — •N. Hollmann, M.W. Haverkort, M. Benomar, M. Reuther, T. Lorenz, and J.A. Mydosh — II. Physikalisches Institut, University of Cologne
This talk presents a study on the magnetic properties of the layered perovskite La2−xSrxCoO4. This class of materials crystallises in the K2NiF4 structure as the high-TC superconductors La2−xSrxCuO4 or the corresponding nickelates La2−xSrxNiO4, the latter exhibiting stripe order of both charge and spin. In many cobaltates, the spin state of the cobalt ions is an extra degree of freedom. The non-layered compound LaCoO3 even shows a thermally driven spin-state transition. Much less is known about the spin states of the cobalt ions in La2−xSrxCoO4. We prepared a series of single crystals by the floating zone method, covering a strontium doping range of 0.3≤ x ≤ 0.8. We measured the magnetic susceptibility for a magnetic field applied parallel and perpendicular to the CoO2 planes. We find a clear deviation from Curie-Weiss behaviour and strong anisotropy. From the direction of the magnetic anisotropy we conclude that χ is dominated by Co2+ in the high-spin state, while Co3+ is in the low-spin state. These findings are confirmed by full-multiplet crystal field calculations which show that spin-orbit coupling and crystal field effects are essential for describing the magnetic behaviour.
Supported by the DFG through SFB 608