Spin Jahn-Teller effect in the antiferromagnet CoTi2O5

ORAL

Abstract

We have used a combination of neutron powder diffraction and muon spin rotation experiments, complemented with DFT calculations, to solve the magnetic structure of orthorhombic CoTi2O5, which we find adapts a long-range ordered, antiferromagnetic state below 26 K with a moment of 2.72(1)μB per Co2+ ion and propagation vector k=(±1/2,1/2,0) [1]. Interestingly, in the experimentally determined crystal structure all the magnetic exchange couplings are completely frustrated by the underlying symmetry. Therefore, we conclude that the magnetic transition must driven by a Spin Jahn-Teller effect, in which the large spin degeneracy is relieved by a distortion of the crystal structure and an associated lowering of the structural symmetry. We investigate this distortion using high resolution x-ray experiments and DFT calculations. Furthermore, we discuss recent experimental studies of FeTi2O5 and the observed similarities to CoTi2O5, which leads us to conlcude that spin-phonon coupling can induce magnetic order in lower symmetry systems than previously reported.

[1] arXiv:1808.01387v1

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Presenters

  • Franz Lang

    University of Oxford

Authors

  • Franz Lang

    University of Oxford

  • Franziska Kirschner

    University of Oxford, Oxford University, Department of Physics, University of Oxford

  • Stephen Blundell

    University of Oxford, Oxford University, Department of Physics, University of Oxford

  • Roger Johnson

    University of Oxford, ISIS Pulsed Neutron Source, Rutherford Appleton Laboratory, Clarendon Laboratory, University of Oxford, Department of Physics, University of Oxford, Physics, University of Oxford

  • Dharmalingam Prabhakaran

    University of Oxford, Physics, University of Oxford, Department of Physics, University of Oxford, United Kingdom