Weak ferromagnetism above T-N in Gd2CuO4

In this work we report magnetization and Raman measurements performed in si ngle 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 stu died the T-dependence of the intensity of these fRm and the WF component be tween 2 and 800 K. The WF component and the relative intensity of the two f Rm decrease with increasing T and they vanish at T similar to 650 and 520 K , respectively. Recent neutron diffraction experiments observed a tetragona l to orthorhombic phase transition at T congruent to 650 K. These results a re interpreted in terms of structural distortions within the CuO2 planes th at lead to the existence of a distribution of coexisting tetragonal and ort horhombic crystallographic domains in this system. (C) 2001 Elsevier Scienc e B.V. All rights reserved.