Local lattice distortions and metal-insulator transition in Nd_0.5Sr_0.5MnO₃ perovskite manganite

High energy temperature-dependent x-ray diffraction coupled with the Atomic Pair Distribution function was employed to reveal the structure model of Nd_0.5Sr_0.5MnO₃ manganite. The system exhibits substantial disorder effects leading to local lattice distortions due to the coexistence of Nd⁺³ and Sr⁺² ions at the same A-atomic site. Surprisingly, the high symmetry model was inadequate to explain local lattice distortions even observed at room temperature. To address this, we explored that low symmetry Monoclinic model S.G. P2₁/m was able to explain the distortions in the present sample. Our results show evidence of charge, orbital ordering CO/OO around 140 K corresponding to metal-insulator transition T_MI followed by a second-order insulator-metal transition T_IM around 261 K. Additionally, the effect of the external magnetic field was examined on our sample which initially was in an antiferromagnetic state AFM, therefore magnetic field was strong enough to melt CO/OO state, rendering system to ferromagnetic state FM state, coinciding with metamagnetic phase transition. I will address how a present work displays a complex interplay between spin, charge, and lattice degree of freedom, and a low symmetry model with constraints was able to explain local lattice instabilities which makes this work unique and interesting. Additionally, how the experiments done in a magnetic field were able to melt the charge ordering/orbital ordering state exhibiting metamagnetic phase transition.