A study on exchange coupled structures of Fe/NiO and NiO/Fe interfaced with n- and p-silicon substrates

Abstract

Interfacial structures of ferromagnetic (FM)/antiferromagnetic (AF) (Fe/NiO) and AF/FM (NiO/Fe) on n- and p-Si substrates have been realized by sequential deposition of FM and AF layers on the silicon substrates by electron beam evaporation technique. The structures have been characterized from x-ray diffraction (XRD), atomic force microscopy (AFM), magnetic force microscopy (MFM), and M-H characteristics. It has been found that there is a strong interfacial intermixing to form the various oxide and silicide phases of Fe2O3, β-Fe2O3, β″-Fe2O3, NiSi, Ni3Si, and Fe5Si3. AFM micrographs show the granular morphology of the top layer of the structure, with a large grain size of ∼400 nm, however, the XRD data show the crystallite size of ∼20 to 70 nm. It seems that the crystallites are clustered to form larger grains. MFM features show a large domain size corresponding to AFM grain size for Fe/NiO/Si structure and very small domain of nanometer size for NiO/Fe/Si structure (having NiO as a top layer). M-H characteristics show that the magnetic behavior is only significant for Fe/NiO/nSi structure with a significant coercivity and exchange bias than for all other interfacial structures of Fe/NiO/pSi, NiO/Fe/pSi, and NiO/Fe/nSi. Thus, it has been found that Fe/NiO/nSi structure can be used in magneto-electronic device applications. It seems that the observed result of significant exchange bias and coercivity is due to the microstructural and chemical structure changes in the antiferromagnetic layer along with the roughness (data as obtained from AFM).