Muon Spin Relaxation Study of Partially Disordered State in Triangular-Lattice Antiferromagnet: Ca_3Co_2O_6 (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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A muon spin relaxation (μSR) experiment has been performed in zero-field (ZF) and longitudinal-field (LF) conditions for a Ca_3Co_2O_6 sample which has an antiferromagnetic triangular lattice on the ab-plane with Ising ferromagnetic chains along the c-axis. At 150K, far above the magnetic transition temperature T_<c1> (=25K) determined from magnetization data, exponential-like relaxation curves are observed in ZF-μSR time spectra, suggesting the development of intrachain ferromagnetic coupling even far above T_<c1>. Below the temperature T_<c2> (〜12K) where magnetization is saturated, the tail of the relaxation curve reaches 1/3 the value of the amplitude in ZF-μSR spectra and the decoupling phenomenon in LF-μSR, that is, a further rise of the tail due to the applied LF, can be observed, implying the appearance of the static internal magnetic field. However, between T_<c1> and T_<c2>, the above-mentioned phenomenon cannot be observed. This indicates that the internal magnetic field at each muon site is not static but rather dynamical with the fluctuation time τ_c (〜21ns) although the magnetization gives large values between these temperatures. This fact must indicate the presence of a partially disordered antiferromagnetic state peculiar to the frustrated magnetic system.
社団法人日本物理学会の論文
2006-03-15