Heavy ion induced modifications on morphological, magnetic and magneto-transport behaviour of exchange-biased Fe/NiO and NiO/Fe bilayers with Si substrate for spintronic applications

Abstract

Exchange-coupled interfacial structures of Fe/NiO and NiO/Fe with pSi substrate have been studied and also the effect of swift heavy ion irradiation on the morphological, structural, transport and magnetic behaviour is reported. The interfacial structures have been characterised from X-ray diffraction (XRD), magnetic force microscopy/atomic force microscopy, X-ray photoelectron spectroscopy and magnetisation characteristics. XRD and X-ray photoelectron spectroscopy studies have shown the formation of various silicide and oxide phases due to the interfacial intermixing across the interfaces which is found to affect the transport and magnetic behaviour. A significant enhancement in exchange bias field and coercivity has been observed for Fe/NiO/pSi interfacial structure on the irradiation (as compared to unirradiated ones). The observed enhanced exchange bias and coercivity on the irradiation has been understood due to creation of uncompensated surface/pinned interfacial spins. Magnetic field-induced enhanced current has been observed at low temperatures (50–250 K) for the irradiated structure suggesting the spin-mixing effect. Low temperature magneto-transport study across the irradiated interface has shown negative magnetoresistance (MR) as compared to unirradiated ones for which positive MR is observed. The observed change in MR at low temperatures has been understood in terms of diffuse scattering at grain boundaries/spin-disorder scattering and/or magnetic polarons. Role of interfacial modification/changes in chemical environment across the interfaces is invoked for the observed changes in magnetic and transport behaviour of the structures. A possible explanation for the observed changes is given.