Investigation of magnetic ordering and origin of exchange-bias effect in doped manganite, Sm0.4Ca0.6MnO3

We have carried out detailed investigations of magnetic ordering and the origin of exchange-bias phenomenology in polycrystalline (Sm0.4Ca0.6MnO3)-Sm-154 perovskite compound by employing dc and ac magnetizations, neutron depolarization, and neutron diffraction techniques. The neutron diffraction study reveals a broad charge ordering transition in the temperature range of 275-150K, manifested by gradually varying structural distortions. DC magnetization and neutron diffraction studies infer a magnetic ordering around 110K. Below similar to 40K, this compound exhibits a large enhancement of the magnetization and an exchange-bias effect (similar to 18kOe at 5K). The exchange-bias effect shows a characteristic temperature and cooling field dependence and a training effect. The compound undergoes a CE-type (checker-board type) antiferromagnetic (AFM) ordering of Mn3+/Mn4+ spins below 110K. The large magnetization below similar to 40K arises from the ferrimagnetic (FIM) ordering of a minority (similar to 5vol.%) non-perovskite phase of Mn3O4. The appearance of exchange bias is ascribed due to the presence of an interface, formed between the FIM (Mn3O4) phase and the main AFM perovskite phase. Our study has implications in giving new directions in the search of large exchange-bias effects in mixed FIM/AFM bulk systems.