【作者】 刘者；

【导师】 费维栋；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2013， 博士

【摘要】 纳米金属软磁材料因具有优异的磁学和电学性能而被广泛研究。影响纳米软磁材料磁性能的关键因素之一是其磁各向异性。本文利用化学镀方法制备了CoFeB薄膜及纳米阵列,利用电镀方法制备了Ni纳米线阵列。研究了磁场对制备态及热磁处理态材料组织和磁性能的影响。利用能谱(EDS)分析、扫描电子显微镜(SEM)观察以及X射线衍射(XRD)分析等手段研究了一维纳米阵列的成分、微观组织和相组成。利用振动样品磁强计(VSM)测试了材料的磁性能。通过研究获得了热磁处理引起的结构弛豫过程对非晶薄膜及纳米管阵列磁性能的影响规律。通过研究可逆与不可逆磁化过程,揭示了一维纳米阵列磁化反转模式的演变规律以及外加磁场对一维纳米阵列磁各向异性的影响机制。由热磁处理引起的原子短程序的改变导致CoFeB非晶薄膜表面出现颗粒状析出物。热处理磁场与膜面法线方向成60°角时,退火态非晶CoFeB薄膜具有最优的综合软磁性能,其饱和磁化强度达到850emu/cm3,矫顽力为25Oe。随着纳米线直径的增加,CoFeB纳米线阵列的磁化反转机制由卷曲(Curling)模式逐渐向卷曲与畴壁横向扩展(Transverse)的混合模式转变。化学镀工艺研究表明,增加敏化-活化的次数可以提高模板的填充率,敏化-活化工艺对纳米线阵列的形貌有很大影响。化学镀过程中施加大于1200Oe的轴向磁场可以使直径200nm的非晶CoFeB纳米线阵列的易磁化方向由垂直轴向转变为平行轴向。这种磁各向异性的转变来源于取向沿轴向的原子对增加而引入的一种“伪”磁晶各向异性。加磁场化学镀使纳米线阵列的磁化反转机制由卷曲与横向畴壁扩展的混合模式转变为单纯的卷曲模式。CoFeB纳米管阵列的轴向磁各向异性随化学镀过程中外加磁场的增加而增强。制备态CoFeB非晶纳米管阵列经过不同温度的热磁处理,磁性能起伏不超过10%,在小磁场下的热稳定性很好。电镀过程中施加轴向磁场可以显著加强Ni纳米线阵列的轴向磁各向异性。外加磁场为600Oe时,纳米线阵列的晶粒最大,(110)织构最强,轴向磁各向异性最强。化学镀(电镀)过程中施加磁场是调控一维纳米阵列磁各向异性的有效手段。非晶纳米线阵列的磁化反转机制随纳米线直径和外加磁场变化而改变。更多还原

【Abstract】 Magnetic materials with low dimensional (such as thin films and nanowires arrays) have been widely studied, for their potential applications in modern high-frequency magnetic devices with smaller size and lower energy consuming. In most cases, magnetic materials with out-of-plane anisotropy are essential. It is focused on the way to control the magnetic anisotropy of low-dimensional magnetic materials. For their high resistant, high saturation magnetization, and low coercivity, Co-based amorphous materials have received much attention. But their properties are sensitive to large and sudden change in temperature, because they are in the sub-stability state commonly. This confined their range of applications. In this thesis, amorphous CoFeB thin films, nanotube arrays, and nanowire arrays are obtained by electroless plating, Ni nanowire arrays are obtained by electrode plating. By applying a magnetic field during the plating process, the magnetic anisotropy of nanowire arrays can be tuned. The structure relaxation of amorphous CoFeB thin film and nanotube arrays are studied by thermo-magnetic treatment (annealing under a magnetic field). The phase composition is determined by X-ray diffraction. The morphology is observed by scanning electron microscope, and the elements ratio is analyzed by energy disperse spectroscopy. co-scan mode is used to analyze the textures in Ni nanowire arrays. The magnetic properties are tested by vibrating sample magnetometer. Combined with hysteresis loops, angular dependent He, and first order reversal curves, the effect of applying a magnetic field during the plating process on the reversal mechanism of nanowire arrays is discussed, and the structural relaxation during the thermomagnetic treatment process of amorphous thin films and nanotube arrays is revealed.Thermomagnetic treatment at different angles between the normal direction of film and the annealing magnetic field affect the properties of amorphous CoFeB films. Thermomagnetic treated at certain angle can improve the magnetic properties of the amorphous film. XRD results show that, the short-range directional order of atoms is increased by the annealing thermomagnetic treatment. This structural relaxation process induced decrement of free volume, some particles appeared on the surface of the films.The axial magnetic anisotropy of amorphous CoFeB nanotube arrays can be enhanced by applying a magnetic field parallel to the long axis during electroless plating process. When the applied field increased, the axial magnetic anisotropy of nanotube arrays is enhanced with the atomic short-range ordering increased. The deposited CoFeB nanotubes have very good thermal stability under small magnetic field。The reversal mechanism of CoFeB nanowire arrays is relevant to the nanowire diameter. The results of angular dependent Hc tests showed that, the reversal mechanism of nanowire array is changed from curling mode to the compound mode of curling and transverse with the diameter increased. CoFeB nanowires with different morphologies are obtained with different electroless plating process. The filling ratio is increased with the sensitization and activation treatment times increased. Blown to dry after rinsed in sensitize and activation solutions, under moderate stiring, with suitable reducing agent concentration, and adding moderate PEG into the electroless plating solution can prevent the premature blocking of pores, which is benefit to fabricate nanowire arrays with high quality. The magnetic anisotropy of amorphous CoFeB nanowire (D>200nm) array can be tuned by applying a magnetic field during plating process. The easy magnetization direction of nanowire array turned from parallel to perpendicular to the long axis with the applied magnetic field increased. The results of first order reversal curves showed that, the irreversible part in nanowire arrays increased by the applied magnetic field. The arrangement of magnetic moments in nanowires is changed. The ordering degree of atom-pairs along the axial direction is increased, and a kind of pseudo-magnetocrystalline anisotropy is formed then. The direction of easy magnetization direction is determined by the shape anisotropy, the pseudo-magnetocrystalline anisotropy, and the interwire magnetostatic interaction.The Ni nanowire arrays obtained in AAO templates with20nm diameter have strong (110) texture. The diffusion degree of (110) texture is increased with the length of nanowire is increased. By applying a axial magnetic field during the plating process, the magnetic anisotropy of Ni nanowire arrays along the direction of field is enhanced, the diffusion degree of (110) texture is changed also. Nanowire arrays plated under the magnetic field of600Oe obtained the lowest diffusion degree of (110) texture, the largest grain size, and the strongest axial magnetic anisotropy.更多还原