STUDY OF SPIN CONFIGURATIONS IN SC2CU2O5 BY MEANS OF POWDER NEUTRON-DIFFRACTION

The crystal structure parameters of paramagnetic Sc2Cu2O5 corresponding to space group P2(1)nb have been refined from 25 K powder neutron diffraction measurements. Similar investigations performed at temperature 1.5 K,well below T-N=15 K, have revealed that the ordered magnetic state is at variance with earlier conclusions drawn from susceptibility data, being more complex. The magnetic unit cell is doubled along the c-direction, corresponding to the propagation vector k = {0,0,1/2}. Among the variety of models considered, three appear to be close to the experimental data: ferromagnetically coupled FM dimers, alternating in the ab plane with ferromagnetic chains, exhibiting 'stacking faults': +++-+++-+++ (model 1 with best fit R(M) = 31%); ferromagnetically coupled AF dimers alternating in the nb plane with ferromagnetic chains (model 2) and chains of ferromagnetically coupled FM dimers (model 3). For all models, the easy axis of the magnetic moments is along [100]. The first two models yield almost the same magnetic moment for Cu2+: mu=(0.92+/-0.06)mu B, whereas for the model 3, mu=(0.73+/-0.06)mu B was obtained.