Structural and electronic effects in GdCu alloy.

We have studied structural and electronic phenomena in GdCu using x-ray diffraction (xrd), photoemission spectroscopic (PES) techniques and band structure calculations. Our structural studies show that the as prepared GdCu sample does not stabilise completely in cubic CsCl phase even at room temperature (RT). The thermal hysteresis is observed in the lattice parameter that appears to be due to strain and dislocations at the surface. The behaviour of the intensity of the most intense xrd peak suggests phase coexistence and structural link with magnetic properties. After undergoing thermal cycling to RT, with an increase in polishing depth, the GdCu sample shows different surface and bulk crystal structures at RT. This behaviour is in contrast to the behaviour of the asprepared one. The surface is predominantly cubic while the bulk exposes more its hidden orthorhombic FeB phase with an increase in the depth of polishing. To understand the manifestation of phase separation on the electronic structure, we have used DFT and DFT + U calculations and PES studies. Our results show the importance of on-site Coulombic interaction in Gd 4f and Cu 3d orbitals. At the Fermi edge, in addition to the significant contribution of Gd 5d and Cu 3d, there is also a contribution of Cu 4p states. The PES studies exhibit chemical potential shift as one compares the asprepared GdCu and the GdCu that has undergone thermal cycling. We have discussed the effect of the chemical potential shift on the valence band and core- level spectra. We believe our results will be helpful in providing insight into the generic property displayed by systems that exhibit strain dominated phase separation.