Dome-Shaped Magnetic Phase Diagram of Thermoelectric Layered Cobaltites

Abstract

Using muon spin spectroscopy we have found that, for both NaxCoO(2) (0.6<or=x<or=0.9) and three- and four-layer cobaltites, a common low temperature magnetic state (which in some cases is manifest as an incommensurate spin density wave) forms in the CoO(2) planes. Here we summarize those results and report an almost dome-shaped relation between the transition temperature into the low-T magnetic state and the composition x for NaxCoO(2) and/or the high-temperature asymptotic limit of thermopower in the more complex three- and four-layer cobaltites. This behavior is explained using the Hubbard model on a two-dimensional triangular lattice in the CoO(2) plane.

Staging model of the ordered stacking of vacancy layers and phase separation in layeredNaxCoO2(xShu1, Huang2, Chu3 et al. 2009Phys. Rev. B1413402View full textAdd to dashboardCite

“…Although crude magnetic-phase mappings in this range before suggest that T N varies between 22-27 K, 3,14 Schulze et al recently found an additional 8 K phase for x ϳ 0.80 and 0.85, which can be obtained only after a slow cooling process. 10 With carefully tuned single crystals in the narrow range of 0.82-0.86, we are able to revisit the magnetic-phase diagram and untangle the mystery of T N variation.…”

Transport properties and magnetic-field-induced localization in the misfit cobaltite [Bi2Ba1.3K0.6Co0.1O4]RS[CoO2]1.97single crystal

“…[28,29,30] In most misfit-layered triangular cobaltitles, such as Ca 3 Co 4 O 9 , (Bi,Pb) 2 M 2 Co 2 O y (M =Ca and Sr), SDW is a common spin ordered state. [10] Determining from the µSR results, however, no SDW exists down to 1.8 K at zero or low field in updoped Bi 2 Ba 2 Co 2 O y , [10] Another point of view is the weak localization in 2D systems, [31,32] which theoretically predicts a logarithmic temperature dependence of the conductivity. [33] The misfit structure leads to the system to be 2-dimensional structurally.…”

“…[1, 2, 3, 4] The complex physical properties include the unconventional superconductivity in water-intercalated Na 0.35 CoO 2 , [5] temperature-dependent Hall effect, [3,6] large negative MR in (Bi,Pb) 2 M 2 Co 2 O y (M=Sr and Ca) and Ca 3 Co 4 O 9 ,[2, 6,7] large thermopower (TEP) with low resistivity,[1, 2] and complicated magnetic structure, [8,9,10] etc. These triangular cobaltites have the common structural unit of CdI 2 -type hexagonal [CoO 2 ] layer, which is composed of edge-shared CoO 6 octahedra.…”

Two dimensionality in quasi-one-dimensional cobalt oxides

“…[1,2,3,4,5] Several researchers reconfirmed later the existence of long-range magnetic order in the layered cobaltites by not only µ + SR [6] but also neutron diffraction experiments. [7] These cobaltites share a common structural component as a conduction path, i.e., the CoO 2 planes, in which a two-dimensional-triangular lattice of Co ions is formed by a network of edge-sharing CoO 6 octahedra.…”