Suppression of charge order and exchange bias effect in Nd_0.5Ca_0.5MnO₃nanocrystalline

An Nd0.5Ca0.5MnO3 (NCMO) sample (average diameter similar to 45 nm) is synthesized by the sol-gel method. The temperature dependence of magnetization indicates that the charge order state is suppressed and a ferromagnetic (FM) transition occurs at similar to 100 K. In addition, the magnetic hysteresis loop at 10K under a cooling field of 10 kOe shifts to both the horizontal and the vertical directions when the measure field is 10 kOe. With an increase in the measure field, both the horizontal and the vertical shifts decrease. When the measure field is 50 kOe, the vertical shift vanishes but the horizontal shift still exists. The observed exchange bias effect is attributed to the exchange coupling between the antiferromagnetic core and the FM shell which embodies spin glass-like surface layers.