The nature of the charge-ordered state in Y_0.5Ca_0.5MnO₃ with a very small average radius of the A-site cations

Abstract

A detailed investigation of Y_0.5Ca_0.5MnO₃ with a very small radius of the A-site cations (r_A)≈1.13 Å reveals the occurrence of a charge-ordering transition in the paramagnetic state, at a relatively high temperature of 260 K. The orthorhombic lattice distortion, as measured by the dimensionless index D, is large (∼1.75%) over the entire 300-100 K range, but the antiferromagnetic interactions become prominent only at low temperatures (<160 K). The charge-ordering gap in Y_0.5Ca_0.5MnO₃, measured by low-temperature vacuum tunnelling spectroscopy, is large (∼0.5eV) and the charge-ordered state is unaffected by the application of a magnetic field of 6 T. The study indicates that the nature of charge-ordering in Y_0.5Ca_0.5MnO₃ which is dominated by the cooperative Jahn-Teller effect and the associated lattice distortion is distinctly different from analogous manganates with larger (r_A).