Weak ferromagnetism above TN in Gd 2CuO 4

Abstract

In this work we report magnetization and Raman measurements performed in single crystals of Gd 2CuO 4. The data show the presence of two forbidden Raman modes (fRm), B 1g ∗ and B 2g ∗ , and weak ferromagnetism (WF) in the CuO 2 planes up to temperatures well above T N Cu ∼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∼650 and 520 K, respectively. Recent neutron diffraction experiments observed a tetragonal to orthorhombic phase transition at T≅650 K . These results are interpreted in terms of structural distortions within the CuO 2 planes that lead to the existence of a distribution of coexisting tetragonal and orthorhombic crystallographic domains in this system.