Spontaneous exchange bias in a nanocomposite of BiFeO$_3$-Bi$_2$Fe$_4$O$_9$

TL;DR

This study reports a significant, path-dependent spontaneous exchange bias in a BiFeO$_3$-Bi$_2$Fe$_4$O$_9$ nanocomposite, with temperature-dependent asymmetry, which could impact future magnetic device applications.

Contribution

It demonstrates the existence of a large, path-dependent spontaneous exchange bias in a specific nanocomposite, revealing new insights into exchange bias phenomena at various temperatures.

Findings

Large exchange bias of 30-60 mT observed

Path dependency of exchange bias depending on measurement history

Peak asymmetry around 200 K with nonmonotonic temperature variation

Abstract

We have observed a large as well as path-dependent spontaneous exchange bias (H$_{SEB}$) ($\sim$30-60 mT) in a nanocomposite of BiFeO$_3$-Bi$_2$Fe$_4$O$_9$ 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 - $\Delta$H$_{SEB}$ - is found to be decreasing nonmonotonically across 5-300 K with a peak around 200 K. The $\Delta$H$_{SEB}$ together with large H$_{SEB}$ could have significant ramification in tuning the exchange bias driven effects and consequent applications.