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arXiv · 0909.4964

Magnetic order and dynamics of the charge-ordered antiferromagnet La1.5Sr0.5CoO4

L. M. Helme·A. T. Boothroyd·R. Coldea·D. Prabhakaran·C. D. Frost·D. A. Keen·L. P. Regnault·P. G. Freeman·M. Enderle·J. Kulda
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Abstract

We describe neutron scattering experiments performed to investigate the magnetic order and dynamics of half-doped La1.5Sr0.5CoO4. This layered perovskite exhibits a near-ideal checkerboard pattern of Co2+/Co3+ charge order at temperatures below ~ 800 K. Magnetic correlations are observed at temperatures below ~ 60 K but static magnetic order only becomes established at 31 K, a temperature at which a kink is observed in the susceptibility. On warming above 31 K we observed a change in the magnetic correlations which we attribute either to a spin canting or to a change in the proportion of inequivalent magnetic domains. The magnetic excitation spectrum is dominated by an intense band extending above a gap of approximately 3 meV up to a maximum energy of 16 meV. A weaker band exists in the energy range 20-30 meV. We show that the excitation spectrum is in excellent quantitative agreement with the predictions of a spin-wave theory generalized to include the full magnetic degrees of freedom of high-spin Co2+ ions in an axially distorted crystal field, coupled by Heisenberg exchange interactions. The magnetic order is found to be stabilized by dominant antiferromagnetic Co2+ -- Co2+ interactions acting in a straight line through Co3+. No evidence is found for magnetic scattering from the Co3+ ions, supporting the view that Co3+ is in the S = 0 state in this material.

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L. M. Helme, A. T. Boothroyd, R. Coldea, D. Prabhakaran, C. D. Frost, D. A. Keen, L. P. Regnault, P. G. Freeman, M. Enderle, J. Kulda. 2009-09-28. Magnetic order and dynamics of the charge-ordered antiferromagnet La1.5Sr0.5CoO4. https://doi.org/10.1103/physrevb.80.134414

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