Neutron diffraction study of metamagnetic phases in ErNi2B2C

Neutron diffraction has been used to determine the magnetic order in the me tamagnetic phases of ErNi2B2C, with the magnetic field applied parallel to the [0 1 0] and [1 1 0] crystallographic axes. Below 6 K, ErNi2B2C has an i ncommensurate antiferromagnetic structure with a modulation along the a-axi s of wavevector delta = (0.55, 0, 0). For both orientations three first-ord er metamagnetic transitions are observed below 6 K as the applied field is increased. The first two transitions are to incommensurate antiferromagneti c states with different values of the a-axis modulation, and the third tran sition is to a saturated paramagnetic state in which the spins are aligned ferromagnetically by the applied field. With the field applied parallel to the [0 1 0] direction, which is the magnetically easy axis, the upper incom mensurate state has an additional ferromagnetic component which is not obse rved with the field applied parallel to the [1 1 0] direction. (C) 2000 Els evier Science Ltd. All rights reserved.