超薄Ni81Fe19薄膜的各向异性磁电阻及磁性能

利用磁控溅射方法制备了一系列超薄Ta(5nm)/Ni81Fe19(20nm)/Ta(3nm)磁性薄膜。着重研究了基片温度、缓冲层厚度对Ni81Fe19薄膜各相异性磁电阻(AMR)及磁性能的影响。利用X射线衍射仪分析了薄膜结构、晶粒取向;用四探针技术测量了薄膜的电阻率和各向异性磁电阻;用FD-SMOKE-A表面磁光克尔效应试验系统测量了薄膜的磁滞回线。结果表明:在基片温度为400℃时制备的Ni81Fe19薄膜具有较大的各向异性磁电阻效应和较低的磁化饱和场,薄膜最大各向异性磁电阻为3.5%,最低磁化饱和场为739.67A/m。基片温度为500℃制备的薄膜,饱和磁化强度Ms值最大。随着缓冲层厚度x的增加,坡莫合金薄膜的AMR值先变大后减小,在x=5nm时达到最大值。     

MnFe2O4纳米薄膜的反常磁性研究

采用磁控溅射法制备MnFe2O4薄膜,利XPS、XRD和MPMS分别对薄膜的成分、结构和磁性进行研究,结果表明,温度导MnFe2O4薄膜中金属离子在A位和B位的分布发生变化,从而导致A亚晶格与B亚晶格磁矩随温度变化规律不同,造成MnFe2O4薄膜出现反常的热磁曲线 负剩磁现象与锰铁氧体的亚晶格磁各向异性与磁场导致的磁矩翻转之间的竞争效应有关。     

溅射法制备Mn-Zn铁氧体薄膜的磁性与微结构

以交替真空溅射的方法使用成分分别为MnFe2O4与ZnFe2O4的双靶制备了成分变化的系列Mn1-xZnxFe2O4铁氧体薄膜,衬底为Si(100)。薄膜的成分通过控制不同靶的溅射时间来进行调整。沉积态的薄膜呈非晶结构,在真空炉中以适当的温度对薄膜进行退火之后能够得到多晶Mn-Zn铁氧体薄膜。组成成分为Mn0.5Zn0.5Fe2O4的薄膜呈现了相对最高的饱和磁化强度。同时还研究了制备条件对薄膜结构与磁性的影响,如溅射氧分压,退火真空度,退火温度及薄膜厚度等等。制备的薄膜相对于块状材料具有较高的矫顽力,进而讨论了应力对薄膜矫顽力的影响。     

Synthesis and magnetic properties of nanocolumnar nickel films deposited in argon-nitrogen atmosphere

Ferromagnetic nickel films with a structure comprising nanocolumns grown perpendicular to a substrate have been obtained by magnetron sputtering of a nickel target in argon atmosphere containing 2 vol % nitrogen. Measurements of X-ray diffraction and investigation of magnetic properties showed that the obtained films consist of a solid solution of nitrogen in nickel. The saturation magnetization of the films is 1.5?C2 times smaller and their Curie temperature is 30 K lower than the corresponding values for pure nickel. The film material exhibits a dimensional effect: as the grain size decreases below 10 nm, the magnetization sharply drops; at a grain size of 0.5 nm, the film possesses no magnetic order.     

具有多层结构的聚合物复合薄膜的介电和磁性能

采用旋涂法制备了 Fe3 O4/聚偏氟乙烯(PVDF)复合薄膜(A)、多壁碳纳米管(MWCNT)/PVDF复合薄膜(B)以及纯PVDF薄膜(P)。利用热压法制备具有3层结构的AAA、ABA及APA 复合薄膜。为了探究层状结构对复合薄膜介电和磁性能的影响,制备了单层膜A作为对比(厚度与AAA复合薄膜相同)。分别研究了薄膜的介电和磁性能。结果表明：由于界面效应,同等厚度的AAA复合薄膜较A膜而言具有较高的介电常数;以B和P薄膜替代AAA结构中间层薄膜后,其中ABA复合薄膜的介电常数高于AAA及APA复合薄膜,同时保持较低的介电损耗。对于磁性能,层状结构对复合薄膜的饱和磁化强度及矫顽力均无明显的影响,而ABA复合薄膜的饱和磁化强度高于AAA及APA复合薄膜,且ABA和APA复合薄膜的矫顽力增加。层状结构设计不仅能够调节复合材料的介电性能和磁性能,而且有利于不同纳米填料的分散,为制备多功能聚合物复合材料提供了一定的借鉴作用。     

ZnFe2O4纳米晶的性能

用ＰＥＧ凝胶法合成出不同平均粒径的ＺｎＦｅ２Ｏ４纳米晶。用ＴＥＭ和ＸＲＤ分析其结构、粒径和形貌。用磁天平仪和红外光谱仪（ＩＲ）等手段研究其性能。结果表明ＺｎＦｅ２Ｏ４纳米晶在室温下有磁性，表面不饱和离子配位数降低。     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Aging effect on coercivity of iron oxide thin films

Changes in magnetic properties for Fe_3-x□_x O₄ (x: oxidation degree) thin films made by reactive sputtering and subsequent heat treatments have been examined under room temperature aging and constant temperature annealing. Aging causes variations in coercivity of insufficiently oxidized films which have a specific resistance of less than 1×10¹ Ω·cm, while the coercivity of γ-Fe₂O₃ (x=1/3) did not change. This phenomenon did not depend on additive elements or preparation method. Other magnetic properties such as saturation magnetization, residual magnetization, squareness ratio and coercive squareness, were not affected by aging for any Fe_3-x □_xO₄ composition. The activation energy for a coercivity change is 0.72-0.95 eV near room temperature for films with a specific resistance below 1×10¹ Ω·cm. It was confirmed that only the coercivity varied at 20°C, while both coercivity and the degree of oxidation changed with annealing at 100°C     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Magnetic measurements with Lorentz microscopy

The electron microscope may be operated in a mode which permits the exploration of the magnetization configurations in thin magnetic films. This mode of operation, known as Lorentz microscopy, is a powerful technique for investigating thin NiFe films because it offers high resolution, because it provides an unequivocal identification of the local magnetization direction, and because it permits correlations to be made between the magnetic structure and the underlying physical (crystallographic) structure of the film. In the past, Lorentz microscopy has found fruitful employment in the analysis of the magnetization configurations of domain walls, in studies of various magnetization reversal processes, and in specialized investigations of unusual magnetic structure. Besides these primarily qualitative investigations, however, some quantitative measurements may be made with this instrument. Such measurements are useful not only because they permit direct evaluation of basic magnetic parameters of films being studied by Lorentz microscopy, but because they afford insight into the fundamental processes which occur in the standard macroscopic magnetic measurements of NiFe films deposited on glass substrates. The following measurements are discussed: 1) determination of the Curie temperature; 2) measurement of the anisotropy field Hkby the standard hysteresigraph and the Feldtkeller techniques; 3) quantitative studies of wall motion by labyrinth propagation and by wall creep; 4) the investigation of anisotropy dispersion by the Crowther and Torok techniques. The accuracy of these measurements is, in general, lower than that of the analogous measurements made by macroscopic methods on films deposited on glass substrates. Nevertheless, macroscopic measurements performed on a film on a glass substrate showed good agreement with Lorentz measurements performed on a simultaneously-deposited film which was suitable for Lorentz microscopy.     

Synthesis of single nanocrystal phase γ′-Fe4N on NaCl substrate by DC magnetron sputtering

The single-phase γ′-Fe₄N nanocrystal magnetic films with grain size of d = 40–60 nm were synthesized on single crystal NaCl (1 0 0) substrate by DC magnetron sputtering at 150 °C. The structure, morphology of the single-phase γ′-Fe₄N films were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and the magnetic properties of samples prepared at different substrate temperatures were investigated by superconducting quantum interference device (SQUID). It is shown that substrate temperature has a significant influence on the crystalline structure and magnetic properties for Fe–N films. As substrate temperature was increased, the saturation magnetization for the deposited films increased, but the coercivity reduced.     

Transparent large-strain thermoplastic polyurethane magnetoactive nanocomposites

Organically modified superparamagnetic MnFe(2)O(4)/thermoplastic polyurethane elastomer (TPU) nanocomposites (0.1-8 wt %) were prepared by solvent mixing followed by solution casting. Linear aliphatic alkyl chain modification of spherical MnFe(2)O(4) provided compatibility with the TPU containing a butanediol extended polyester polyol-MDI. All MnFe(2)O(4)/TPU nanocomposite films were superparamagnetic and their saturation magnetization, σ(s), increased with increasing MnFe(2)O(4) content. All nanocomposite films exhibited large deformations (>10 mm) under a magneto-static field. This is the first report of large actuation of magnetic nanoparticle nanocomposites at low-loading levels of 0.1 wt % (0.025 vol %). The maximum actuation deformation of the MnFe(2)O(4)/TPU nanocomposite films increased exponentially with increasing nanoparticle concentration. An empirical correlation between the maximum displacement, saturation magnetization, and magnetic nanoparticle loading is proposed. The cyclic deformation actuation of a 6 wt % surface modified MnFe(2)O(4)/TPU, in a low magnetic field 151 < B(y) < 303 Oe, exhibited excellent reproducibility and controllability. MnFe(2)O(4)/TPU nanocomposite films (0.1-2 wt %) were transparent and semitransparent over the wavelengths from 350 to 700 nm.     

Reversible ferromagnetism study in un-doped ZnO thin films

Room temperature ferromagnetism in pure ZnO thin films prepared by spin-coating method was observed. X-ray photoelectron spectroscopy and inductively coupled plasma-mass spectrometry showed no or extremely little presence of impurities, which were unlikely to be responsible for the large magnetization moment observed. In order to study the origin of ferromagnetism, ZnO thin films were rapidly annealed in N2 and O2 ambient in a repetitive way. Electrical and magnetic performance after each annealing was measured. It is found that ferromagnetism is diminished and re-appeared, in accordance with the decrease and increase of conductivity. Cathodoluminescence spectra show evidence of reversible variation of oxygen vacancy defect in the annealing process. These results provide strong evidence that oxygen vacancies play a significant role in inducing ferromagnetism in ZnO thin films.     

退火温度对NiZn铁氧体薄膜性能的影响

采用射频磁控溅射法在Si(100)基片上制备了NiZn铁氧体薄膜,研究了退火温度对薄膜性能的影响.采用XRD分析仪分析了薄膜的相结构,原子力显微镜分析了薄膜的表面形貌,振动样品磁强计测量了薄膜的磁性能,结果表明,随着退火温度的升高,薄膜的结晶状态越好,晶粒尺寸越大,饱和磁感应强度越高,面内矫顽力越小.     

Effect of vacuum magnetic annealing on the structural and physical properties of the Ni and Al co-doped ZnO films

About 300 nm-thick Zn_0.87Al_0.06Ni_0.07O, Zn_0.83Al_0.06Ni_0.11O and Zn_0.81Al_0.04Ni_0.15O films were deposited on glass substrates at 300 K by co-sputtering ZnO:Al and Ni targets. The films were annealed in vacuum at 673 K for 2 h under a magnetic field of 4.8 × 10⁴ A/m applied along the film plane and then were cooled down to room temperature without magnetic field. All the films have a wurtzite structure and consist of thin columnar grains perpendicular to the substrate. The annealing promotes the (002) orientation growth in the film growing direction for the Zn_0.87Al_0.06Ni_0.07O and Zn_0.83Al_0.06Ni_0.11O films as well as the (100) orientation growth for the Zn_0.81Al_0.04Ni_0.15O film. The annealing results in a slight increase in the grain size. A weak Ni diffraction peak was detected for the annealed films with high Ni content. The annealing enhances the room temperature ferromagnetism of the films. A temperature dependence of magnetization confirms that the Curie temperature is above 400 K for the annealed films. The films magnetically annealed exhibit an anisotropic magnetization behavior. The annealed Zn_0.87Al_0.06Ni_0.07O film has the lowest resistivity (8.73 × 10⁻³ Ω cm), the highest free electron concentration (1.73 × 10²⁰ cm^− 3) and Hall mobility (4.16 cm²V^− 1 s^− 1). A temperature dependence of the resistivity from 50 K to 300 K reveals that the carrier transport mechanism is Mott's variable range hopping in the low temperature range and thermally activated band conduction in the high temperature range.     

Ag底层对TbFeCo薄膜磁性能的影响

采用射频磁控溅射法在玻璃基片上制备了TbFeCo/Ag非晶垂直磁化膜，研究了Ag底层厚度对TbFeCo薄膜磁性能的影响。原子力显微镜、振动样品磁强计与磁光盘测试仪测量结果表明：薄的银底层具有较高的表面粗糙度可以显著增大TbFeCo薄膜的矫顽力，改善TbFeCo薄膜的磁光温度特性，该薄膜有望用作高密度垂直记录介质与光磁混合记录介质。     

掺杂Mg对纳米CoFe2O4/SiO2复合薄膜结构和磁性的影响

采用溶胶-凝胶旋涂法制备了纳米Co_1-xMg _xFe₂O₄/SiO₂(x = 0, 0.2, 0.4, 0.6, 0.8) 复合薄膜。利用XRD、SEM、原子力显微镜、振动样品磁强计对薄膜的结构、形貌和磁性进行了分析, 研究了Mg²⁺含量对样品结构和磁性的影响。结果表明, 样品中Co_1-xMg _xFe₂O₄具有尖晶石结构, 晶粒尺寸在38~46 nm之间。随着Mg²⁺含量的增加, Co_1-xMg _xFe₂O₄的晶格常数减小, 样品的饱和磁化强度减小, 矫顽力先增大后减小。样品Co_0.4Mg_0.6Fe₂O₄/SiO₂垂直和平行膜面的矫顽力分别为350.7 kA·m^-1和279.4 kA·m^-1, 剩磁比分别为67.2%和53.9%, Co_1-xMg _xFe₂O₄/SiO₂复合薄膜具有较明显的垂直磁各向异性。     

Magnetic and structural properties of Co ion-implanted GaN

A GaN epilayer was grown on Al/sub 2/O/sub 3/ substrate by metal-organic chemical vapor deposition, and Co/sup -/ ions with a dose of 3/spl times/10/sup 16/ cm/sup -2/ were implanted into GaN at 350/spl deg/C. The implanted samples were postannealed at 700/spl deg/C-900/spl deg/C to recrystallize the samples and to remove implantation damage. We have investigated the magnetic and structural properties of Co ion-implanted GaN by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and X-ray photoelectron spectroscopy (XPS). XRD results did not show any peaks associated with the second phase formation, and only the diffraction from the GaN layer and substrate structure were observed. The temperature dependence of magnetization taken in zero-field-cooling and field-cooling conditions showed the features of superparamagnetic system in films annealed at 700/spl deg/C-900/spl deg/C. The magnetization curves at 5 K for samples annealed at 700/spl deg/C-900/spl deg/C exhibits ferromagnetic hysteresis loops, and the highest residual magnetization (M/sub R/) and coercivity (H/sub c/) of M/sub R/=1.5/spl times/10/sup -4/ emu/g and H/sub c/=107 Oe were found in the 800/spl deg/C annealed sample. XPS measurement showed the metallic Co 2p core levels and the metallic valence band spectra for as-implanted and 700/spl deg/C-900/spl deg/C annealed samples. From these, it could be explained that the magnetic property of our films originated from Co and CoGa magnetic clusters.     

退火处理Fe(Co)Al(Zr)O系薄膜磁性能的研究

采用射频磁控溅射装置在氩气氛下制备了Fe(Co)Al(Zr)O系薄膜.用X射线衍射仪、透射电镜及其选区衍射来分析薄膜的微结构.用振动样品磁强计、磁导计等测量了矫顽力Hc、饱和磁化强度Ms及磁导率等磁性参数.通过退火处理研究了Fe(Co)Al(Zr)O系薄膜的磁性能.Fe(Co)Al(Zr)O系薄膜磁各向异性是由形状各向异性引起的.