Exchange bias of NiO/FeNi ordered nanocaps on curved substrate

The magnetic NiO / Fe 19 Ni 81 nanostructure bilayer is deposited onto the colloidal spheres grown on a Si wafer by the self-assembly technology. The nanocap and the nanodot arrays form on the spherical surface and the Si substrate, respectively, which are confirmed by scanning electron microscopy and transmission electron microscopy measurements. Compared to the flat bilayer with the same composition deposited on the Si substrate, the exchange bias field H E from the nanocap is twice as large. The enhancement of H E in the nanocap is ascribed to the decreased thickness of the ferromagnetic layer induced by the sphere surface. The size and space of the biased caps are estimated based on the thickness variations induced by the sphere surfaces.