Magnetic and electronic structure of the frustrated spin-chain compound linarite PbCuSO₄(OH)₂

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