2024/10/24 by Mingyu Xu, Haozhe Wang, Xu, Mingyu +29
Physics and Astronomy · Materials Science · #Advanced Condensed Matter Physics #Magnetic and transport properties of perovskites and related materials #Physics of Superconductivity and Magnetism
paper · pdf · doi:10.48550/arxiv.2410.18826
The interplay between crystal electric field splitting of d states and Hund's rule exchange energy in cobalt-based perovskites offers a promising avenue for inducing spin-state transitions. This study reports a new body-centered tetragonal (BCT) phase of BaCoO3 (BCT-BaCoO3), synthesized under high pressure (15 GPa) and high temperature (1200 °C) conditions. BCT-BaCoO3 adopts a double perovskite structure of EuTiO3-type (space group I4/mcm, #140), confirmed by high-resolution scanning transmission electron microscopy. X-ray photoelectron spectroscopy reveals a rare Co4+ valence state. Magnetization and X-ray absorption measurements reveal a low-spin to high-spin transition that takes place between 200 and 300 K. While spin crossovers are relatively common among common oxides, the one observed in BCT-BaCoO3 is remarkable in that it proceeds in the opposite direction from conventional spin transitions. BCT-BaCoO3 exhibits a low-spin (S = 1/2) state at high temperatures and transitions to a high-spin (S = 5/2) state at low temperatures. Within the high-spin state, hard ferromagnetic order onsets at TC = 107 K. Electrical resistivity indicates weak magnetoresistance and insulating behavior. Overall, BCT-BaCoO3 presents an exceptional model for the exploration of spin-state transitions and the study of Co spin states in cobalt-based perovskites.