Weak ferromagnetism above TN in Gd2CuO4

In this work we report magnetization and Raman measurements performed in single crystals of Gd2CuO4. The data show the presence of two forbidden Raman modes (fRm), B-1g(*) and B-2g(*), and weak ferromagnetism (WF) in the CuO2 planes up to temperatures well above T(N)(Cu)similar to 280 K. We have studied the T-dependence of the intensity of these fRm and the WF component between 2 and 800 K. The WF component and the relative intensity of the two fRm decrease with increasing T and they vanish at T similar to 650 and 520 K, respectively. Recent neutron diffraction experiments observed a tetragonal to orthorhombic phase transition at T congruent to 650 K. These results are interpreted in terms of structural distortions within the CuO2 planes that lead to the existence of a distribution of coexisting tetragonal and orthorhombic crystallographic domains in this system. (C) 2001 Elsevier Science B.V. All rights reserved.