Abstract book - phy

P-3 45
NMR study of incommensurate helical
magnetic order in the spin-chain
cuprates LiCu 2 O 2 and NaCu 2 O 2
A.A. Gippius 1 , N. Buettgen 2 , W. Kraetschmer 2 , M. Baenitz 3 ,
L.E. Svistov 4 , A.S. Moskvin 5 , A.A. Bush 6
1 Moscow State University, 119991 Moscow, Russia
2 University of Augsburg, D-86135 Augsburg, Germany
3 MPI for Chemical Physics of Solids 01187 Dresden Germany
4 Institute for Physical Problems, 119334 Moscow, Russia
5 Ural State University, 620083 Ekaterinburg, Russia
6 Moscow Institute of Radiotechnics, 117464 Moscow, Russia
A 7 Li NMR study of a LiCu 2 O 2 single crystal without twinning was performed
in the temperature range around the transition into the magnetically
ordered state. The transition into the incommensurate (IC) low-temperature
helical phase occurs in two successive stages at temperatures T c1 = 24.7 K
and T c2 = 22.8 K. The 7 Li NMR line shape evolution was studied in detail
in the temperature range 22 K – 25 K in an external field around 7.7 T applied
along the main crystallographic axes. The observed 7 Li NMR spectra
in the intermediate temperature range differ considerably from those obtained
in the low-temperature phase (T < T c2 ). This yields a clear signature
of the different character of the IC magnetic structures of Cu 2+ spins in
the intermediate and low-temperature phases, respectively. The 7 Li NMR
results are compared with the 23 Na NMR spectra obtained in a NaCu 2 O 2
single crystal [1] and are discussed in terms of both helical and collinear IC
magnetic structures of Cu 2+ spins.
[1] A.A. Gippius et al., Physical Review B 77 (2008) 180403R