Ferrimagnetic correlations in paramagnetic ErCO2.

We have performed X-ray magnetic circular dichroism experiments on ErCo2 in order to measure the Er and Co net magnetic moments above and below its ferrimagnetic transition. The results demonstrate the occurrence of an unexpected antiparallel alignment of Co and Er sublattices almost 30 K above the magnetic transition. We attribute this antiparallel alignment to magnetic short-range order. We have characterized the temperature dependence of the magnetic correlation length (xi) with small angle neutron scattering measurements. We observe the expected divergence of xi right above T-c and, a wide region well within the paramagnetic phase, where the correlation length has an almost constant value of 7 angstrom. We have further observed a direct correlation between Co magnetic moment and xi: at the onset of the long range order both magnitudes experience an abrupt increase, while the temperature range at which xi has a constant value coincides with the change of sign of the Co magnetic moment. (c) 2006 Elsevier B.V. All rights reserved.