Europhys. Lett.
Volume 70, Number 5, June 2005
Page(s) 677 - 683
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 04 May 2005
Europhys. Lett., 70 (5), pp. 677-683 (2005)
DOI: 10.1209/epl/i2004-10519-4

Observation of magnetic excitons in $\chem{LaCoO_3}$

S. R. Giblin1, I. Terry1, S. J. Clark1, T. Prokscha2, D. Prabhakaran3, A. T. Boothroyd3, J. Wu4 and C. Leighton4

1  Department of Physics, University of Durham - South Road, Durham, DH1 3LE, UK
2  Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut CH-5332, Villigen, PSI, Switzerland
3  Department of Physics, University of Oxford - Oxford, OX1 3PU, UK
4  Department of Chemical Engineering and Materials Science, University of Minnesota 421 Washington Ave SE, Minneapolis 55455, USA

received 25 November 2004; accepted in final form 14 April 2005
published online 4 May 2005

An impurity-driven magnetic phase transition has been investigated in $\chem{LaCoO_3}$ at temperatures below that of the thermally induced spin state transition of the $\chem{Co^{3+}}$ ion. We have discovered a saturating component of the magnetisation, which we attribute to previously unobserved interactions between magnetic excitons. These conclusions are confirmed by muon spin spectroscopy which indicates an ordering temperature of 50$\un{K}$ in both the transverse and zero-field configurations. Low-energy muon measurements demonstrate that the magnetic behaviour is independent of implantation energy and hence a property of the bulk of the material. The magnetic exciton formation is attributed to the interaction between electrons bound at oxygen vacancies and neighbouring cobalt ions, and is proposed as the precursor to the magneto-electronic phase separation recently observed in doped lanthanum cobaltite.

76.75.+i - Muon spin rotation and relaxation.
75.30.Hx - Magnetic impurity interactions.

© EDP Sciences 2005