A common behaviour of thermoelectric layered cobaltites: incommensurate spin density wave states in [Ca₂Co_4/3Cu_2/3O₄]_0.62[CoO₂] and [Ca₂CoO₃]_0.62[CoO₂]

Phase separation in theCoO2layer observed in thermoelectric layered cobalt dioxides

“…That is, a transition to a short-range order of the IC-SDW state at Ϸ180 K with decreasing T was found; then the long-range order and a 3D antiferromagnetic ͑AF͒ ͑or FR͒ order appeared below Ϸ140 and Ϸ85 K, respectively. 20 Quite recently, we have performed 59 Co nuclear magnetic resonance ͑NMR͒ measurements on the latter compound, and the observed 59 Co NMR spectra with varying T were in agreement with the phase diagram. 21 In the lattice of MLCO's, there are at least two Co sites, namely, one is in the CoO 2 layer and the other is in the rock-salt layer.…”

The effect of pressure on the spin density wave transition in the layered cobaltites [Ca2CoO3]0.62[CoO2] and [Ca2Co4/3Cu2/3O4]0.62[CoO2]

“…Nevertheless, the position of the first and second minima in the spectrum obtained at 0.1 MPa is approximately same to that at 1.3 GPa. Indeed, the value of n m Zu m /2p at 5 K is estimated as 66G3 MHz under 0.1 MPa and 65G2 MHz under 1.3 GPa; here, n m (0 K)Z64 MHz without pressure cell [11]. This suggests 1) and (2).…”

“…The polarization S m of the decay muon is antiparallel to the muon irajectory, and thus perpendicular to the c-axis aligned sample. This is important because the volume fraction of the magnetic phase was w100% in the c-aligned sample and a clear muon precession caused by the IC-SDW field is observed only when S m tc [10,11].…”

“…the CoO 2 planes, in which a two-dimensionaltriangular lattice (2DTL) of Co ions is formed by a network of edge-sharing CoO 6 octahedra. In previous positive muon spin rotation and relaxation (m C SR) experiments on a variety of layered cobaltites, we found that a common low temperature magnetic state (which in some cases is manifest as an incommensurate spin density wave, IC-SDW) forms in the CoO 2 planes [8][9][10][11][12][13]. Since the SDW state is induced by the competition between electron correlation and spin concentration in the CoO 2 2DTL [14][15][16], the nature of the SDW state is considered to be essentially same for all layered cobaltites.…”

“…½CoO 2 (3-layer cobaltite) [8,10] and w64 MHz for ½Ca 2 Co 4=3 Cu 2=3 O 4 RS 0:62 ½CoO 2 (4-layer cobaltite) [11]. The internal magnetic field (H int ) at the m C site is g m H int Zn m , where g m (Z13.55342 kHz/G) is the muon gyromagnetic ratio.…”