Magnetic properties of Yb2Cu2O5 by powder neutron diffraction

The powder neutron diffraction study performed at low temperatures has revealed that the ordered magnetic state is at variance with earlier conclusion and is more complex. At 4.2 K, assuming a single propagation vector k = {0, 1/2 , 1/2 }, the best fit has been achieved for the model with the following arrangement of Yb3+ and Cu2+ moments: Yb: {Cx(1) Cx(2)}, Cu: {Ay(1) Ay(2), -Az(1) -Az(2)}. The detailed analysis of experimental data indicates that for a better description of magnetic ordering, two propagation vectors are needed. No magnetic ordering was detected at 10 K. Bearing in mind the specific structural features of this system, in particular the chain structure of copper dimers and weak interchain coupling, it is concluded that below 15 K copper moments order first in lower dimension, whereas the 3D ordering occurs with further lowering of temperature below 7.5 K.