Antiphase boundary-driven large exchange bias and negative magnetoresistance in NiCo2O4

Abstract

Nickel-based spinel oxide has recently attracted significant attention due to its remarkable magneto-transport properties, promising various spintronic applications. In this study, we observe an exchange bias effect, where the magnetic hysteresis loop shifts both horizontally and vertically when single-phase nanocrystalline NiCo2O4 is cooled in the presence of an external magnetic field. The magnitude of the exchange bias field is approximately 375 Oe at 5 K, and this effect disappears around 300 K. Furthermore, NiCo2O4 shows semiconducting behaviour in longitudinal resistivity and demonstrates a substantial negative magnetoresistance of ~31.5% at 10 K. The magnetoresistance exhibits a butterfly-shaped behaviour at low magnetic fields and becomes almost linear at high magnetic fields. A detailed analysis of the negative magnetoresistance and exchange bias reveals that both phenomena originate from the formation of antiphase boundaries in the as-synthesized NiCo2O4 sample, as confirmed by the high-resolution transmission electron micrograph.