MAGNETISM IN THE RARE-EARTH CUPRATES R2CU2O5 (R=Y,HO,ER,YB,TM)

The magnetic structures at 1.5 K of R2Cu2O5-type compounds appear to be commensurate having propagation vectors k = [0, 0, 0] for Y, Er and Tm, k = [0, 1/2, 0] for Ho and k = [0, 1/2,1/2] for Yb. In all cases, except for Yb, we found that both Cu and R sublattices order simultaneously. The magnetic moments for Cu sites show the same relative arrangement. The ordering of magnetic moments in the R sublattices differs strongly between the different compounds, indicating the existence of a strong competition between the crystal-field and the exchange interactions. From the magnetic structures determined we explain the metamagnetic-like transitions observed in the magnetization curves.