Morphology and magnetic properties of island-like Co and Ni films obtained by de-wetting

The morphological, structural, and magnetic properties of Co and Ni films of different thicknesses grown by RF sputtering on a Si-SiO substrate and submitted to controlled diffusion of atoms on the substrate (de-wetting) are studied through X-ray diffraction (XRD), atomic force microscopy, X-ray photoelectron spectroscopy, and alternating-gradient magnetometry. For both metals, de-wetting treatment leads to the growth of non-percolating, metallic nanoislands characterized by a distribution of sizes and aspect ratios. XRD spectra reveal a polycrystalline multi-component structure evolving by effect of de-wetting and directly affecting the magnetic properties of films. The magnetic response after de-wetting is consistent with the formation of a nanogranular magnetic phase characterized by a complex, thickness-dependent magnetic behavior originating from the simultaneous presence of superparamagnetic and blocked-particle contributions. At intermediate film thickness (around 10 nm), a notable enhancement in magnetic coercivity is observed for both metals with respect to the values measured in precursor films and in their bulk counterparts.