| Ferromagnetic metal nanowires have high saturation magnetization and obvious anisotropy,so they have been considered as potentially valuable materials for magnetic storage.The measurement of magnetization and coercive force of ferromagnetic nanowire arrays is affected by the magnetic behavior inside each nanowire.The study of magnetic moment reversal and microdynamics inside a single nanowire is of great significance to the development and application of magnetic storage and the establishment of magnetization mechanism.In recent years,electron holography has been used to study the magnetization vector distribution,domain structure and magnetization flip mechanism in low dimensional nanometer magnetic samples.In this paper,ferromagnetic metals Fe,Co and Ni nanowires were prepared by alternating current deposition using anodic aluminum oxide(AAO)as template.The macroscopic magnetism,microstructure,magnetization vector distribution and magnetization reversal mechanism of these nanowires were studied.The results are as follows:1.Based on AAO template,ferromagnetic metal Fe,Co,Ni nanowire arrays were prepared by alternating current deposition method.The nanowire arrays were investigated by X-ray diffraction(XRD).The results show that Fe nanowires are body-centered cubic crystals and grow preferentially along the [110] direction.Ni nanowires are face-centered cubic crystals and grow preferentially along the [111]crystal direction.Co nanowires have a hexagonal close-packed crystal structure with[1000] crystal orientation and polycrystalline orientation.2.The ferromagnetic nanowires were tested by MPMS at room temperature.The results show that the shape anisotropy has a significant effect on the magnetic properties of nanowires.3.Transmission electron microscope(TEM)showed that the diameter of the nanowires was about 40 nm,which was consistent with the diameter of the template hole,indicating that the nanowires grew along the hole and filled it.The composition of the nanowires was determined by energy dispersive X-ray spectroscopy(EDS).The results show that the elemental Fe,Co and Ni nanowires were obtained by alternating current deposition.4.The crystal structure of nanowires was characterized by high resolution(HRTEM)mode of transmission electron microscopy and selected area electron diffraction(SAED)mode.The results show that the crystal orientation of single nanowires is consistent with the XRD test results.The crystal structure of the nanowires was obtained and verified by simulation software5.The domain structure of nanowires in demagnetization is obtained by using the Fresnel model of Lorentz microscope.The domain structure is related to magnetic anisotropy energy.Off-axis electron holography(EH)was used to obtain the hologram of nanowires,and the phase map containing magnetic information was obtained by reconstruction of the hologram.The distribution of magnetic induction lines in the nanowires under demagnetization was obtained by the phase map.6.Based on the theory of micromagnetism,the simulation of single nanowire and nanowire array is carried out by using OOMMF software: 1.The magnetization process of nanowires is simulated theoretically,and the simulated results are in good agreement with the experimental results.2.The magnetization process of nanowires with different aspect ratios was simulated,and the results showed that the coercive force was affected by the change of aspect ratio.3.The magnetization process of a single nanowire was simulated,and the magnetization reversal behavior of the magnetic moment inside the nanowire driven by the external field was recorded.The reversal mechanism of the nanowire was determined to be the crimp mode by combining with the magnetic phase diagram obtained from the experiment.The simulated results are in good agreement with the measured magnetization process of nanowire arrays. |
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