The effects of thickness variation on the physical properties of Al-doped NdNiO3 thin films

Abstract

NdNiO3 is the prototype of RNiO3 (R=Rare earth ion) type strongly correlated systems which show metal-to-insulator transitions (MITs), mainly because of structural change. The RNiO3 class of materials demonstrates a fascinating phase diagram where NdNiO3 and PrNiO3 show simultaneous magnetic and electronic transitions along with a structural transformation, unlike other RNiO3 materials. At low temperatures below MIT, these materials show insulating behaviour due to a charge disproportion. The charge disproportion arises due to the conversion of Ni3+ to Ni2+ and Ni4+. An isovalent doping by Al3+ doping at the Ni3+ site should hinder this conversion and affect the electronic states. With this idea in mind, we previously studied Al-doped NdNiO3 thin films and found that a small level of doping, like 5%, is enough to show a reasonable effect. Based on our earlier studies, we chose to synthesize 5% Al-doped NdNiO3 thin films on LAO (001) single crystal substrate of varying thickness (10, 20, and 30 nm) using pulsed laser deposition (PLD) to understand the effects of thickness variation in the combination of Al-doping. We studied the films using X-ray diffraction (XRD) for phase formation, temperature-dependent Raman spectroscopy for structural modifications, and temperature-dependent resistivity for electronic behaviour. We present our results here in this thesis with detailed discussions.