Volume 80, Number 2, October 2007
Article Number 27005
Number of page(s) 6
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 20 September 2007
EPL, 80 (2007) 27005
DOI: 10.1209/0295-5075/80/27005

Muon-spin rotation study of magnetism in NaxCoO2 single crystals with 0.78 $\leqslant$ x $\leqslant$ 0.97

C. Bernhard1, 2, Ch. Niedermayer3, A. Drew1, G. Khaliullin2, S. Bayrakci2, J. Strempfer2, R. K. Kremer2, D. P. Chen2, C. T. Lin2 and B. Keimer2

1  University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials (FriMat) Chemin du Musee 3, CH-1700 Fribourg, Switzerland
2  Max-Planck-Institute for Solid State Research - Heisenbergstrasse 1, D-70569 Stuttgart, Germany
3  Paul-Scherrer-Institut - CH-5232 Villigen PSI, Switzerland

received 19 July 2007; accepted in final form 1 September 2007; published October 2007
published online 20 September 2007

By muon spin rotation we investigated the magnetic properties of a series of highly Na-doped NaxCoO2 single crystals with 0.78(1) $\leqslant$ x $\leqslant$ 0.97(1). Our data provide evidence for an intrinsically inhomogeneous magnetic state which can be described in terms of hole-doping (Na vacancy)-induced magnetic clusters that percolate at 1-x $\gtrsim$ 0.04 until they yield a bulk magnetic state near x = 0.78. Evidence for a strong (likely geometrical) frustration of the magnetic order is obtained from the anomalous doping dependence of the spin fluctuation rate (above the ordering temperature) which is strongly enhanced at x = 0.78 as compared to x = 0.97.

71.27.+a - Strongly correlated electron systems; heavy fermions.
75.25.+z - Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.).
76.75.+i - Muon spin rotation and relaxation.

© Europhysics Letters Association 2007