Significant softening of c66 and hidden order parameter in the magnetic ordered state of La2-xCaxCoO4 (0.4≤x≤0.7)

K. Horigane, T. Kobayashi, M. Suzuki, K. Abe, K. Asai, J. Akimitsu

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4 Citations (Scopus)


We have measured the longitudinal and transverse sound velocities of La2-xCaxCoO4 (0.4≤x≤0.7) propagating along [100], [110], and [001] from 200 K down to 3 K with a frequency of 10 MHz. It was found that c66 shows a remarkable softening below Co 2+ spin-ordering temperature TN in the whole doping range, while c11-c12/2 exhibits a clear hardening below Co 3+ spin-ordering temperature TN2 only when x=0.5. To explain the observed anomaly, the Landau free energy for the La 2-xCaxCoO4 system has been constructed, including the coupling energy between elastic strains and a two-dimensional order parameter (Q1, Q2), having a spatial modulation along [110] or [1̄ 10]. We argued that this represents orbital order, and it is this order that leads to the softening of c66.

Original languageEnglish
Article number144108
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number14
Publication statusPublished - Oct 27 2008
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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