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
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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.
KeywordsInterfacial Structure Exchange Bias Exchange Bias Effect Exchange Bias Field Nuclear Energy Loss
The authors would like to acknowledge the help received from Pelletron group, Inter University Accelerator Centre (IUAC), New Delhi, India during the irradiation experiments. The authors are thankful to Dr. D. K. Avasthi and Dr. D. Kabiraj for their involvement during irradiation experiments and Dr. Indra Sulania, Scientist (IUAC, New Delhi, India) for performing MFM/AFM measurements. The authors are also thankful to Dr. T. Shripathi (Scientist ‘H’, UGC-DAE-CSR, Indore, India) for providing the access to XPS measurement and related fruitful discussions. One of the authors (N. Srivastava) is grateful to Council of Scientific and Industrial Research (CSIR), New Delhi, India for providing the financial support in the form of Senior Research Fellowship (CSIR-SRF).
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