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Center for Nonlinear Studies |
We study a frustrated quantum Ising model relevant for Ca3Co2O6 that comprises a triangular lattice of weakly coupled ferromagnetic chains. Our quantum Monte Carlo simulation shows that the chains become ferromagnetic and form a three-sublattice “up-up-down” structure in the lowest-T regime below T=T_{CI}. In contrast, long-period spin-density-wave (SDW) modulations along the chains are stabilized for T_{CI} < T < Tc in agreement with recent experiments by Agrestini et al [1]. We also discuss a simple mean-field theory revealing quasi-continuous change of the modulation periodicity as a function of T, implying the existence of metastable states in the SDW phase, which explains the slow low-temperature dynamics that has been observed in Ca3Co2O6 [2]. Closely related multiferroic material Ca3MnCoO6 [3] will also be discussed. References: [1] S. Agrestini et al., Phys. Rev. Lett., 101, 097207 (2008) [2] T. Moyoshi and K. Motoya, J. Phys. Soc. Jpn., 80, 034701 (2011) [3] Y. J. Jo et al., Phys. Rev. B. 79, 012407 (2009)
Host: Kipton Barros, T-4 and CNLS