Spontaneous exchange bias in a nanocomposite of BiFeO₃-Bi ₂Fe₄O₉

We have observed a large as well as path-dependent spontaneous exchange bias (H_SEB) (∼30-60 mT) in a nanocomposite of BiFeO ₃-Bi₂Fe₄O₉ across 5-300 K when it is measured in an unmagnetized state following zero-field cooling and appropriate demagnetization. The path dependency yields a variation in the exchange bias depending on the sign of the starting field and the path followed in tracing the hysteresis loop. The asymmetry thus observed-ΔH_SEB-is found to be decreasing nonmonotonically across 5-300 K with a peak around 200 K. The ΔH_SEB together with large H_SEB could have significant ramification in tuning the exchange bias driven effects and consequent applications.