METAMAGNETIC TRANSITION IN Y2CU2O5

Neutron diffraction experiment has been performed to determine the mag netic structures in magnetic fields up to 6 T on a single crystal of Y 2Cu2O5 which shows strange metamagnetic transitions at H-e1 = 3.0 T an d H-c2 = 4.8 T for H parallel to b. At H = 0, the determined magnetic structure is identical with that obtained for the powder sample, but n ew diffraction peaks appear at completely unexpected positions between H-c1 and H-c2, which means a three-lattice period modulation along th e b-axis but this structure change is mysterious from the crystallogra phic point of view. (C) 1998 Elsevier Science B.V. All rights reserved .