A common behavior of thermoelectric layered cobaltites: anincommensurate spin density wave state detected by muon spin rotation andrelaxation


J. Sugiyama1, H. Itahara1, J. H. Brewer2,E. J. Ansaldo3, K. Dohmae1, C. Xia1, Y. Seno1,

B. Hitti4, T. Tani1


1Toyota Central Research and Development Labs. Inc.,Nagakute, Aichi 480-1192, Japan

2TRIUMF, CIAR and Department of Physics and Astronomy,University of British Columbia, Vancouver, BC, V6T 1Z1 Canada

3Department of Physics, University of Saskatchewan,Saskatoon, SK, S7N 5A5 Canada

4TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 Canada


Magnetism of misfit layeredcobaltites, [Ca2CoO3]0.62RS[CoO2]and [Ca2Co4/3Cu2/3O4]0.62RS[CoO2](RS means a rocksalt-type block), was investigated by a positive muon spinrotation and relaxation (m+SR) experiment. For [Ca2CoO3]0.62RS[CoO2],a transition to an incommensurate (IC) spin density wave (SDW) state was foundbelow 100 K (= TSDWon)and a clear oscillation due to a static internal magnetic field was observedbelow 30 K (= TSDW), while TSDWon = 180 K and TSDW = 140 K for [Ca2Co4/3Cu2/3O4]0.62RS[CoO2].The large transition width (= 40 - 70 K) suggested that a short-range IC-SDWorder appeared below TSDWon anda long-range order completed below TSDW. Furthermore, an anisotropic behavior of the zero-field m+SR spectra on the c axis aligned samples indicated that the IC-SDWpropagates in the a-b plane, with oscillatingmoments directed along the c axis. Theseresults suggest that the IC-SDW exist not in the rocksalt-type block but in theCoO2 plane.