CRYSTAL-STRUCTURE REFINEMENT AND MAGNETIC-ORDERING IN HO2CU2O5, TM2CU2O5, YB2CU2O5 COMPOUNDS

The crystal structures of R2Cu2O5(R=Ho, Tm, Yb) compounds have been refined by the powder neutron diffraction method. All compounds investigated are isostructural and crystallize in the orthorhombic Ho2Cu2O5 type of crystal structure corresponding to space group Pn21a. The long-range magnetic ordering existing at low temperature in Ho2Cu2O5 and Yb2Cu2O5, predominantly associated with rare earth ions has been determined. In Ho2Cu2O5 the magnetic unit cell is doubled along the c-axis, corresponding to k=[0, 0, 1 2]. In Yb2Cu2O5 the magnetic cell is doubled along the b and c directions i.e. k=[0, 1 2, 1 2]. The magnetic moments at saturation are: in Ho2Cu2O5 either μHo=(8.2±0.1)μB (μHo | b, Cu moments not ordered) or μHo=(8.2±0.1)μB, μCu=(1.2±0.1)μB, both aligned along the b-axis. In Yb2Cu2O5 the magnetic moments μCu=(0.7±0.1)μB of copper are aligned along the a-axis. The magnetic moment of ytterbium has x and z components, equal to (1.3±0.1)μB and (0.7±0.1)μB, respectively. © 1990.