Suppression Of Charge Ordering Transition By The Reduction In Particle Size In The Manganite Bi0.2ca0.8mno3

We have prepared a series of Bi0.2Ca0.8MnO3 samples with different particle sizes ranging from 60 to 1500 nm by the sol-gel method and systematically investigated their static and dynamic magnetic properties through dc magnetization, ac susceptibility, and electron spin resonance measurements. It was found that the reduction in particle size suppresses the charge ordering (CO) transition in this composition, resulting in the occurrence of the spin glass state in low temperatures. The observations have been interpreted in terms of martensitic strain and surface effect. Moreover a scenario has been posed for the waning process of the CO transition. With the reduction in the particle size, the CO phase transition survives only in the core regions until its complete disappearance, and connected with this, the magnetic cluster phenomenon becomes more pronounced.