非晶Co-Pt合金纳米线有序阵列的制备及其磁学性质

通过直流电沉积方法，以多孔阳极氧化铝(AAO)为模板，在室温下成功制备出一维非晶态Co-Pt合金纳米线有序阵列. SEM和TEM分析表明：纳米线长度均约10 μm，直径35 nm；纳米线在阳极氧化铝模板孔内互相平行. XRD结果表明，制备的纳米线为非晶态结构，经过700 ℃退火处理后则转变为面心立方(FCC)多晶结构. 采用VSM(振动样品磁强计)对退火处理前后样品的矫顽力和剩磁比进行研究，结果表明：当外加磁场与纳米线平行时，非晶态Co-Pt合金纳米线的矫顽力高达1700 Oe，剩磁比为0.83，表现出明显的垂直磁各向异性；而退火处理则使其优秀的磁学性质消失. 退火前后不同的磁学性质源于其不同的微观结构. 非晶态的Co-Pt合金纳米线由于无磁晶各向异性竞争，进而使得由纳米线一维形态引起的形状各向异性起主导作用，使其显示了很好的垂直磁各向异性；而多晶样品由于磁晶各向异性与形状各向异性竞争，导致矫顽力和剩磁比迅速降低.

Preparation and Magnetic Properties of Amorphous Co-Pt Alloy Nanowire Arrays

Highly ordered amorphous Co-Pt alloy nanowire arrays are prepared by electrodepositing it into anodized aluminum disks with nanosized pores. SEM and TEM images reveal that the nanowires of array are uniform, well isolated, and parallel to each other. The average length of the Co-Pt alloy nanowires is about 10 μm and the typical diameter is about 35 nm. Its microstructures and magnetic properties are also investigated by XRD and VSM (vibrating sample magnetometer), respectively. The sample prepared by the electrodeposition shows perpendicular anisotropy, but the as-annealed sample does not show. These different magnetic behaviors before and after annealing can be attributed to their different microstructures. X-ray diffraction evidences show that the sample before annealing is amorphous, but it changes to be polycrystalline after annealing. In the poly-crystalline sample, due to the competition of shape anisotropy and magnetocrystal anisotropy, the sample does not display perpendicular anisotropy. But magnetocrystal anisotropy is very small in amorphous sample， there-fore, shape anisotropy plays a dominant role which leads to strong perpendicular anisotropy.