Multilayered core/shell nanostructures
Magnetic monolayer nanostructures are limited in their functions. The trend toward multifunctional and high-density devices requires fabrication of multilayer core/shell nanostructures. Because of their geometry, the internal and external structures can be close enough to interact via a strong dipolar coupling. This interaction can produce new magnetic states of the cylindrical particle as a whole , which can be used for potential applications in spintronics, multiferroics, etc. Besides, we can expect the appearance of new magnetic properties, like dipolar magnetic bias . The possibility of achieving such a spin-valve-like hysteresis loop is very attractive because of potential applications in sensing magnetic fields in magnetic recording systems.
Recently, Daly et al. reported the synthesis and characterization of highly ordered cobalt–magnetite nanocable arrays. Chong et al. synthesized Fe3O4/SiO2/Ni core/shell nanowires by using ALD and electrodeposition methods. They observed two distinct magnetic switching events, confirmed theoretically by Sarli et al. Chen et al. reported the synthesis and magnetic characterization of Co/NiO/Ni core/shell nanotube arrays by direct electro-deposition. Besides, GaN/Fe core/shell nanowires have been investigated for nonvolatile spintronics on Si. Also, a method for synthesizing Ge1−xMnx/a-Si core/shell nanowires using a supercritical fluid deposition technique has been reported by Barth et al. Zierold et al. have demonstrated a template-based synthesis route for preparing novel, multilayered magnetic nanotubes for suspension in liquids. Finally, Soroka et al. produced double and triple-walled TiO2/iron oxide nanotubes with well defined interfaces in nanoporous alumina templates using ALD.
On this topic, we have studied the magnetic configurations present in these systems . Besides, we investigated the magnetostatic interaction between the inner and outer tube when both are axially magnetized  and when one of them is reversing its magnetization . Furthermore, we have shown that the dipolar field of the external layer originates a bias of the hysteresis loop . The inhomogeneity of this field is responsible for the existence of different reversal processes, which lead to non-symmetrical hysteresis loops.
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