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 Neelabh Srivastava 1,2 • P. C. Srivastava 1 Received: 7 July 2015 / Accepted: 31 July 2015 / Published online: 12 August 2015 Ó Springer Science+Business Media New York 2015 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 mor- phological, 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 spec- troscopy and magnetisation characteristics. XRD and X-ray photoelectron spectroscopy studies have shown the for- mation 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 signifi- cant 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 sug- gesting the spin-mixing effect. Low temperature magneto- transport study across the irradiated interface has shown negative magnetoresistance (MR) as compared to unirra- diated 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 polar- ons. 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. Introduction Exchange coupling phenomenon between magnetic thin films/multilayers in which the magnetisation of one layer is influenced by the proximity of another layer can be exploited to make spin-dependent electronic devices such as spin valves, magnetoresistive random access memory and giant magnetoresistance read heads [1, 2]. The phe- nomenon of exchange bias has been extensively studied since its discovery for more than 50 years ago by Meik- lejohn and Bean in ferromagnetic (FM) Co particles sur- rounded by a layer of antiferromagnetic (AF) CoO [3]. It is well known that when a system of FM/AF is cooled through the Neel temperature (T N ) of AF with Curie tem- perature, T C [ T N , exchange bias (EB) is induced in the system. In spite of several intensive experimental and theoretical investigations, several aspects of the underlying mechanism are still lacking due to the lack of information about the structural and chemical environments across the interface which may affect the interface magnetic structure. Different models [4–8] have been proposed earlier to explain the exchange bias phenomenon which claims that the exchange bias effect is of interfacial origin, but it also involves several layers of AF moments. Therefore, it is very sensitive to the microstructure of the bilayer and also to its interface. So, the arrangement of spins at the interface often plays a very crucial role in determining their & Neelabh Srivastava neelabh.mdl@gmail.com 1 Department of Physics, Banaras Hindu University, Varanasi, UP 221005, India 2 Institut fu ¨r Halbleiteroptik und Funktionelle Grenzfla ¨chen (IHFG), Allmandring 3, Universita ¨t Stuttgart, 70569 Stuttgart, Germany 123 J Mater Sci (2015) 50:7610–7626 DOI 10.1007/s10853-015-9321-5