Competing interactions and dimensional crossover in (Er0.5Y0.5)2Cu2O5 studied by EPR

Copper spin dynamics in (Er0.5Y0.5)2Cu2O5 solid solution has been investigated by electron paramagnetic resonance (EPR) technique. The temperature dependence of the EPR integrated intensity of the resonance line has showed a pronounced maximum at low temperatures and has vanished at the transition to the antiferromagnetic ordering at TN = 11 K. The temperature at which the EPR integrated intensity reaches maximum was different for the heating and cooling runs. Study of the product of integrated intensity and temperature has allowed determination of the dominating interactions in a particular temperature range. A model used previously to describe the AFM modes in the antiferromagnetic state of Y2Cu2O5 was applied to explain the observed changes in the EPR spectra. A dimensional crossover from 2D to 3D magnetic behaviour was observed at 55 K and interpreted in terms of the spin correlation length.