Fabrication And Magnetic Properties Research Of Co Nanowires And Sm-Mn Alloy Nanotubes

The research on fabrication and magnetic properties of magnetic nanowires or nanotubes array has gradually become a hot project. In this paper, Co nanowires and Sm-Mn nanotubes have been successfully fabricated in nano-pores of the anodic aluminum oxide (AAO) templates by DC electrochemical deposition method. The AAO templates include commercial templates and self-made templates. The crystalline structure and morphology of samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), and the compositions were confirmed by energy dispersive spectrometry (EDS). The magnetic properties of samples were measured by vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID).In this experiment, well-ordered porous anodic alumina template is obtained by the two-step anodic oxidation method. We would obtain the templates with different diameter by adjusting the opening and expanding pores time. When the time is about180min, the pore diameter is about54nm. When the time is approximately390min the pore diameter is close to the limit,105nm.Using the AAO templates with different pores diameter, the Co nanowires were fabricated with the diameter of76nm,105nm,215nm and300nm, respectively. With the deposition voltage changing from-0.95V to-1.15V, the crystal structure of Co nanowire arrays have a transition from the single crystalline to polycrystalline state. Magnetic measurement shows Co nanowire arrays have the obvious magnetic anisotropy, and the easy magnetization axis is perpendicular to the axis of the nanowires. The anisotropy is determined by the competition among the shape anisotropy, magnetostatic interaction and magnetocrystalline anisotropy. Here, the magnetostatic interaction plays an important role, which induces the easy axis perpendicular to the nanowires. The Co nanowires appear the exchange bias phenomenon after high temperature annealing treatment in air. It is due to anti ferromagnetic oxide layer formed in the surface of Co nanowires.Sm-Mn nanotubes with the diameter of76nm,105nm,215nm and300nm, respectively, have been fabricated in AAO templates. The EDS analysis indicates that nanotubes are composed of Sm and Mn element. XRD, HRTEM and SEAD analysis prove that the crystal structure of the nanotubes is amorphous, without preferential growth orientation. Magnetic measurement shows that Sm-Mn nanotube arrays have the obvious magnetic anisotropy, and the easy magnetization axis is parallel to the axis of nanotubes. This is mainly determined by the shape anisotropy. The coercivity gradually increases, the magnetostatic interaction decreases and the shape anisotropy become stronger as the diameter of Sm-Mn alloy nanotubes decreases.