Electrochemical Preparation, Structure And Magnetic Magnetic Nanowires

Magnetic nanowires display extremely superior performance in comparison to macroscopic material due to their large aspect ratio. They have been widely investigated not only due to their intriguing magnetic properties but also their potential applications in ultra-high density data storage and spintronics.Magnetic anisotropy is one of the most important factors to determine the magnetic properties of ferromagnetic nanowires, which primarily includes magnetocrystalline anisotropy and shape anisotropy. For Fe, Ni and fee Co nanowires, the magnetocrystalline anisotropy is considerably smaller than the corresponding shape anisotropy and can be neglected, thus the shape anisotropy plays a dominant role in magnetic properties. While for hcp Co nanowires, the magnetocrystalline anisotropy is comparable to the shape anisotropy and may play an important role in magnetic properties of Co nanowires. Consequently, magnetic anisotropy of Co nanowires can be adjusted in a large extent.Several kinds of methods can be used to fabricate nanowires, such as lithographic patterning and template synthesis. Low-cost electrodeposition through anodic aluminum oxide (AAO) templates is widely employed due to its convenience. In this work, Co nanowires have been fabricated into AAO templates by dc electrodeposition. The microstructure of Co nanowires is adjusted by controlling the deposition temperature and deposition voltage.The structure of the Co nanowires was carried out by X-ray diffraction with Cu-Ka radiation, high resolution transmission electron microscopy and selected area electron diffraction. At a given electrodeposition temperature, the dc electrodeposition at lower and higher voltages results in the hep structure with preferred [100] orientation along the nanowire axis and fee structure with a preferred [220] orientation along the nanowire axis, respectively. Two structures coexist for a medium voltage (transition voltage). A high electrodeposition temperature leads to the increase of the transition voltage.A vibration sample magnetometer and VersaLab magnetometer were used to measure the magnetic properties of the samples. For hcp Co nanowires, the competition between magnetocrystalline anisotropy and shape anisotropy results in a weaker effective anisotropy along the nanowire axis and the magnetization reversal is mainly dominated by curling-like mode. With temperature increasing from50K to390K, easy axis switches towards the nanowire axis due to the decreasing magnetocrystalline anisotropy and a minimal coercivity is observed. In turn, fcc Co nanowires exhibit longitudinal uniaxial anisotropy. The magnetization reversal at room temperature undergoes a change from curling-like mode at small angles to coherent-like mode at larger angles. Moreover, shape anisotropy is predominant in the whole temperature range. Thus, the decreasing magnetocrystalline anisotropy leads to the increasing of the coercivity along the nanowires at higher temperatures.The magnetic properties of ferromagnetic metal can be significantly changed by introducing non-magnetic metals. CoxAg1-x nanowires have been fabricated into AAO templates with a wide range of deposition voltage by dc electrodeposition. The XRD results show that the samples are amorphous. When deposition voltage higher than1.6V, easy axis is aligned along the nanowire axis. While for1.6V, the sample is paramagnetic. The magnetic properties of the system have been greatly improved due to the presence of Ag, compared to Co nanowires deposited at the same voltage (2.0V).