【作者】 张志城；

【导师】 黄志高；

【作者基本信息】 福建师范大学 ， 凝聚态物理， 2007， 硕士

【摘要】 本文从磁性纳米线有序阵列的制备、性能测试到模拟计算、理论解释等一系列的工作研究纳米线的磁特性与磁化反转过程。主要工作如下：(1)实验上，采用两步阳极氧化法制备了有序孔洞的阳极氧化铝(Anodic Aluminum Oxide，AAO)模板。原子力显微镜和扫描电镜测试结果表明实验室获得的AAO模板孔径一致、孔间距均匀，适合于做一维纳米材料的模板。(2)在有序孔洞的AAO模板上交流电沉积磁性纳米线阵列，重点研究了纳米线孔径大小和外场与纳米线线轴夹角θ对矫顽力的影响。实验结果表明：不同直径的Co纳米线有序阵列的矫顽力随着θ的增大而减小；纳米线直径的增大引起其矫顽力的减小，而纳米线天然的形状各向异性则引起三种直径的Co纳米线均表现出明显的垂直各向异性，易磁化轴平行于纳米线轴线方向，不同直径的Co纳米线易轴方向具有高矫顽力和高矩形比的特点，适合于超高密度磁记录。(3)引进超声振荡技术对AAO模板进行处理，在AAO模板中无电沉积铁镍合金纳米材料，振动样品磁强计测量结果表明样品具有明显的垂直各向异性，易磁化轴垂直于模板表面，而且各向异性随着沉积时间的增加而变得更加明显。而矫顽力不随外场方向改变的结果可能是由于制备态的铁镍合金为非晶结构的缘故。(4)理论上，应用Monte Carlo模拟研究纳米线的磁化反转机制。首先，分别用一致转动模型、不考虑磁晶各向异性和考虑磁晶各向异性3个模型模拟了单根纳米线的磁滞回线，得到矫顽力对角度θ的依赖关系。理论和实验的对比结果表明经典的一致转动模型对于解释纳米线的磁化反转过于简单，应考虑磁晶各向异性对Co纳米线磁性的重大影响。磁化反转组态说明，对单根纳米线，小角度时磁化反转主要以局域化成核—传播为主；而大角度时，单根纳米线磁化反转更接近于一致转动模式。更多还原

【Abstract】 In this thesis, ordered magnetic nanowire arrays were fabricated and studied. Theoretically, number simulation was conducted to figure out the magnetic properties and the mechanism of magnetization process. The contents were summarized as following:Firstly, ordered porous Anodic Aluminum Oxide (AAO) template was prepared by two-step anodization method. The results from atom force microscope (AFM) and scanning electron microscope indicated that our home-made AAO templates have uniformed diameters and interpore distances. The AAO template was very suitable to fabricate 1 D (one dimension) nanostructure materials.Secondly, ordered magnetic nanowire arrays were deposited into AAO by alternating current electrodeposition (AC electrodeposition). Emphasis was imposed on the relations between coercivities field and different magnetic field orientations as well as nanowire diameters at room temperature. The measured coercivity as a function of angle (θ) between the field and wire axis revealed that the coercivity decreased with increasing the value ofθfor various Cobalt nanowires electrodeposited into AAO template. Although the coercivity decreased with increasing the nanowire diameter, all the Co nanowire displayed evident perpendicular magnetic anisotropy, with its easy axis along the nanowire. The point was ascribed to the natural shape anisotropy of nanowire. In addition, all the Co nanowires shared the characteristics of large coercivities and high squareness ratio, which revealed that the naonwire arrays have potential application on ultrahigh density magnetic recording.Then, with the introduction of ultrasonic vibrating technique into the pretreatment of AAO template, the iron and nickel alloy nanostructure materials were electrolessly plated in AAO templates. Vibrating sample magnetometer (VSM) tests indicated the alloys also displayed evident perpendicular magnetic anisotropy, with its easy axis parallel to the nanowire. What’s more, the longer the plating time extended, the more the perpendicular anisotropy was. The independence of coercivities with external field orientation was due to the amorphous structure of as-deposit alloy.At last, based on Monte Carlo simulation, we investigated the magnetization reversal modes of the Co nanowire. The hysteresis loops and, so the angle dependence of coercivity were obtained by three models, e.g. coherent rotation, with and without the consideration of magnetocrystalline anisotropy. Comparing the simulated with the experimental results, it was found that the magnetocrystalline anisotropy played an important role on the magnetic properties of Co nanowires, and the magnetization reversal process in the Co nanowires could not easily be understood by the classical coherent rotation mode. Magnetization reversal configurations revealed that the magnetization reversal in Co nanowires with small angles was nucleation-propagation process, while in large angles it was similar to coherent rotation.更多还原