Temperature dependence of exchange bias in NiFe2O4/BiFeO3 bilayers

Abstract

In BiFeO3-based ferromagnet/anitferromagnet (FM/AFM) bilayers, field cooling is required through the Néel temperature to achieve significant exchange bias (EB) at room temperature (RT). In this work, NiFe2O4/BiFeO3 (NFO/BFO) all-oxide bilayer films were selected and deposited on SrTiO3 substrates by pulsed laser deposition to avoid the possible interfacial oxidization during the field cooling process. In combination with X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM) characterizations, the NFO/BFO bilayers are shown to have good crystalline layered structure. After field cooling at various temperatures, the samples show sizable EB effect at low temperature region, which is attributed to spin-glass-pinned effect. More importantly, significant EB can be obtained at RT after the sample was field cooled from temperatures higher than 400 K. The maximal values of the exchange bias field (HE) and the ratio between HE and coercivity (i.e. HE/HC) are 48 Oe and 0.6 at RT, respectively. The EB effect at RT is considered to result from the pinned and uncompensated spins near the NFO-BFO interface.