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TT: Fachverband Tiefe Temperaturen
TT 13: Symposium “Superconductivity and Magnetism in Lamellar Cobaltates”
TT 13.4: Talk
Tuesday, March 27, 2007, 15:40–16:05, H18
Magnetic phase separation in highly Na doped NaxCoO2 with x > 0.75. — •Christian Bernhard1, Li Yu1, Alexander Boris2, Dapeng Chen2, Chengtian Lin2, Bernhard Keimer2, and Christof Niedermayer3 — 1Universität Fribourg, Chemin du Musee 3, CH-1700 Fribourg, Switzerland — 2Max-Planck-Insitut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany — 3Paul-Scherrer-Institut, CH-5232 Villigen-PSI, Switzerland
We report muon spin rotation and infrared ellipsometry measurements on NaxCoO2 single crystals with 0.75<x<1 that provide evidence for an intrinsic phase separation scenario. At the highest Na content of x=0.97 we observe isolated magnetic clusters which have a small total spin of about S=1 and undergo a spin freezing transition around Tsf ∼ 20 K. With decreasing Na content the cluster begin to overlap developing extended antiferromagnetic patches with TN=22 K. A bulk long-range ordered state occurs near x=0.75. The optical data establish a highly anomalous charge transport with signatures of a strong spin charge coupling which is explained in terms of a hole doping induced spin state transition of the Co3+ ions.