Particle-size effects on the suppression of charge ordering in Nd0.8Na0.2MnO3

Abstract

In this work, we have studied the suppression of the charge-ordered (CO) state in Nd0.8Na0.2MnO3 compound by varying the particle size and the applied magnetic field. The bulk samples with a particle size of D ≥ 140 nm exhibit different magnetic ground states, such as paramagnetic (PM), charge-ordering, ferromagnetic-cluster-glass (FM-CG), and reentrant-spin-glass-like (RSG) behavior. The complete suppression of charge ordering could be observed by reducing the particle size down to 50 nm. The field variation of magnetization curves at different temperatures show field-induced reversible transition from the antiferromagnetic (AFM) CO state to the FM state beyond a threshold field (HC). The M–H loops recorded at 5 K, show a distinct field-induced transition from a spin-frozen state to a FM state, especially on bulk samples with particle sizes of D ≥ 140 nm. T–H phase diagrams were constructed for samples with different particle sizes. The phase boundary between CO-AFM and FM states was found to shift toward higher temperature and lower magnetic fields with a decrease in particle size. Moreover, the phase-separation region was also found to narrow down with a decrease in particle size. The boundary of the spin-frozen state is found to shift toward lower temperature and magnetic field with decrease in particle size. The observed result could be explained based on the core-shell model.