Neutron diffraction investigation of the metamagnetic transition in Y2Cu2O5

Y2Cu2O5 shows two successive metamagnetic transitions for magnetic fields (B) parallel to the b-axis, one at Bc1∼2.8 T and one at Bc2≅4.7 T. Above Bc2 the magnetisation gradually increases and saturates at Bs ∼ 7.3 T. Generally such metamagnetic transitions are not expected in a Cu2+ spin system because of the small anisotropy and hence have never before been observed in this type of compounds. We performed neutron diffraction experiments in zero an applied fields parallel to the b-axis to shed some light on the nature of these metamagnetic transitions. An unexpected magnetic structure with tripling of the unit cell in the b-direction has been observed for applied fields of Bc1 < B < Bc2. The possible magnetic structures compatible with the crystal structure symmetry have been determined by means of symmetry analysis and these results are compared to the neutron diffraction and magnetisation data. (author)