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Abstract:
We present an extensive microscopic magnetic study of the
quasi-one-dimensional frustrated s = 1/2 spin-chain compound linarite.
Angular-dependent susceptibility and H-1-NMR measurements were performed
at various temperatures in the paramagnetic state. All relevant NMR
parameters, viz., the chemical, the dipolar, and the Fermi-contact
contribution, were extracted to analytically calculate the local
magnetic fields at the H-1 sites. From this analysis, a significant spin
transfer of similar to 11% from the magnetic copper ions onto the two
oxygen ligands was derived. This result is compared to LSDA+U
calculations, which further can explain the significant reduction of the
coupling constants of the compound compared to other edge-sharing CuO
chains due to the presence of specific OH bonds in linarite. The
magnetically ordered spin-spiral ground state for T < 2.8 K was
investigated by H-1-NMR for fields mu H-0 = 2.0 T along the three
crystallographic main directions. With the derived NMR parameters in the
paramagnetic regime it is possible to model the NMR spectrum of the
magnetically ordered state for H parallel to c. A deviation observed
between the NMR data and the evaluated spectrum for H parallel to b is
discussed in terms of a significant rearrangement of the spiral state in
an applied field of mu H-0 = 2.0 T for this direction.
