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

doi:10.1103/PhysRevB.78.144108

Significant softening of c₆₆ and hidden order parameter in the magnetic ordered state of La_2-xCa_xCoO₄ (0.4≤x≤0.7)

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

Research output: Contribution to journal › Article › peer-review

4 Citations (Scopus)

Abstract

We have measured the longitudinal and transverse sound velocities of La_2-xCa_xCoO₄ (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 T_N in the whole doping range, while c₁₁-c₁₂/2 exhibits a clear hardening below Co ³⁺ spin-ordering temperature T_N2 only when x=0.5. To explain the observed anomaly, the Landau free energy for the La _2-xCa_xCoO₄ 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 language	English
Article number	144108
Journal	Physical Review B - Condensed Matter and Materials Physics
Volume	78
Issue number	14
DOIs	https://doi.org/10.1103/PhysRevB.78.144108
Publication status	Published - Oct 27 2008
Externally published	Yes

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Condensed Matter Physics

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

abstract = "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 [{\=1} 10]. We argued that this represents orbital order, and it is this order that leads to the softening of c66.",

author = "K. Horigane and T. Kobayashi and M. Suzuki and K. Abe and K. Asai and J. Akimitsu",

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T1 - Significant softening of c66 and hidden order parameter in the magnetic ordered state of La2-xCaxCoO4 (0.4≤x≤0.7)

AU - Horigane, K.

AU - Kobayashi, T.

AU - Suzuki, M.

AU - Abe, K.

AU - Asai, K.

AU - Akimitsu, J.

PY - 2008/10/27

Y1 - 2008/10/27

N2 - 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.

AB - 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.

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Significant softening of c₆₆ and hidden order parameter in the magnetic ordered state of La_2-xCa_xCoO₄ (0.4≤x≤0.7)

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