![]() ![]() It is found that the coercivity and the EB of the nanowires have been improved evidently by forming the α-Fe 2O 3 core-shell structure. The structure, morphologies, and magnetic properties of the resulted nanowires have been comprehensively studied. In this paper, α-Fe 2O 3 core-shell nanowires with novel fluffy-like α-Fe 2O 3 covered on the surface were synthesized. Therefore, the synthesis of one-dimensional Fe-based nanostructures and varying the magnetic properties via chemical control over the components could be important for the understanding of EB at the nanoscale level. The large aspect ratio, the high surface area to volume ratio, the shape anisotropy, and the interface play important roles in the magnetization dynamics of the core-shell structured systems. For the one-dimensional nanowires, the magnetic properties are even more complicated. However, the physical origin of EB is still poorly understood. Up to now, the EB effect of Fe-based nanostructures, for example, zero-dimensional core-shell NPs of Fe/ γ-Fe 2O 3, FeO/Fe 3O 4, and Fe/Fe 3O 4 have been systematically investigated. For example, for the typical ferromagnetic (FM)/antiferromagnetic (AFM) hybrid magnetic system, the EB appears when the sample is cooled down from above the AFM N éel temperature in an external field. It is characterized by the horizontal shift of the hysteresis loops after the hybrid magnetic systems cooled down through the critical temperature in an external field. The EB was first observed by Meiklejohn and Bean in oxide-coated Co particles in 1956. As a result, strong exchange magnetic coupling between the iron core and the oxide shell alters the magnetic anisotropy, giving rise to the modifications of the coercivity ( H C) and the appearance of the exchange-bias (EB) effect. To avoid such a situation, encapsulating Fe nanostructures through the passivation with a Fe-oxide layer is adopted to both protect and stabilize the Fe nanostructures and thus form the core-shell morphology. However, one of the crucial problems in obtaining Fe nanostructures is that they commonly burn up when they are put into contact with air due to the strong activity of Fe. Furthermore, due to the special morphology, it usually exhibits many novel and unique physical characters, including magnetoimpedance (MI) effect, nanoscale confinement, and nanomagnetism, etc.Īs the most commonly used magnetic element, iron (Fe)-based nanostructures have stimulated great interest for researchers in the past few decades. Comparing with other nanostructures, nanowires, especially ferromagnetic metal nanowires, have attracted more attention owing to their fundamental importance for various fields such as environmental remediation, biomedicine, magnetic sensors, and magnetic storage devices, etc. In recent decades, the synthesis and properties of nanostructures have been greatly motivated both by a large number of potential applications and by fundamental questions about the physics of nanoscale magnetism. The large values of coercivity and exchange field, as well as the high surface area to volume ratio, may make the fluffy α-Fe 2O 3 core-shell nanowire a promising candidate for the applications of the magnetic drug delivery, electrochemical energy storage, gas sensors, photocatalysis, and so forth. The magnetic measurements show that the effective anisotropy is increased with increasing the thickness of the α-Fe 2O 3 by annealing. Both the coercivity and the exchange field increase with increasing annealing time ( T A) and reach their maximum values of 1,042 and 78 Oe, respectively, at T A = 4 h. Through the annealing process in air, the coercivity and the exchange field are evidently improved. The coercivity of the as-synthesized nanowires is above 684 Oe in the temperature range of 5 to 300 K, which is significantly higher than that of the bulk Fe (approximately 0.9 Oe). Novel fluffy α-Fe 2O 3 core-shell nanowires have been synthesized using the chemical reaction of ferrous sulfate and sodium borohydride, as well as the post-annealing process in air. ![]()
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