Hidden magnetic transitions in the thermoelectric layered cobaltite [ Ca 2 CoO 3 ] 0.62 [ CoO 2 ]

摘要: A positive muon spin rotation and relaxation $({\ensuremath{\mu}}^{+}\mathrm{SR})$ experiment on $[{\mathrm{Ca}}_{2}{\mathrm{CoO}}_{3}{]}_{0.62}[{\mathrm{CoO}}_{2}]$ (i.e., ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9},$ a layered thermoelectric cobaltite) indicates the existence of two magnetic transitions at $\ensuremath{\sim}100\mathrm{K}$ 400--600 K; former is transition from paramagnetic state to an incommensurate (IC) spin-density wave (SDW) state. The anisotropic behavior zero-field ${\ensuremath{\mu}}^{+}\mathrm{SR}$ spectra 5 K suggests that IC-SDW propagates in $a\ensuremath{-}b$ plane, with oscillating moments directed along c axis; also found exist not $[{\mathrm{Ca}}_{2}{\mathrm{CoO}}_{3}]$ subsystem but $[{\mathrm{CoO}}_{2}]$ subsystem. In addition, it long-range order completes below $\ensuremath{\sim}30\mathrm{K},$ whereas short-range appears 100 K. latter interpreted as gradual change Co ions above 400 These detected by are correlate closely transport properties $[{\mathrm{Ca}}_{2}{\mathrm{CoO}}_{3}{]}_{0.62}[{\mathrm{CoO}}_{2}].$