Magnetic Properties of Single Crystalline Co2MnAl Heusler Alloy Thin Films

Ferromagnetic resonance measurements were carried out for single crystalline Co₂MnAl thin films as a function of the angle between applied external magnetic field and normal of the film surface. In- and out-of-plane angular dependence of the resonance field and only out-of-plane angular dependence of the linewidth of FMR spectra were analyzed using the Landau?CLifshitz?CGilbert equation. The easy and hard axes were determined by analyzing the in-plane angular dependence of resonant field. The films annealed at various temperatures showed four-fold magnetic anisotropy symmetry and the damping factor was estimated from the analysis of the angular dependency of FMR spectra.     

Heusler合金Co2MnAl1-xGex的电子结构、磁性和半金属性

基于密度泛函理论(DFT),使用广义梯度近似(GGA)和局域密度近似(LDA)研究了Heusler合金Co2MnAl1-xGex(x=0、0.25、0.5、0.75、1)的磁性和电子结构。随着掺杂浓度x的增加,合金的晶格常数和磁矩都线性增加,分别很好地满足Vegard和S-P规律。对于整个合金系列,随x的增加,自旋向下带带隙宽度略有减少,费米面向高能移动。由于Co2MnAl0.5Ge0.5合金的费米面恰好居于其自旋向下带带隙中部,此时合金具有最好的半金属稳定性,预期在磁隧道结器件中能实现高的自旋极化率。     

Influence of Annealing Temperatures on Structural and Magnetic Properties for Cr-Based Inverse Heusler Alloy Nanoparticles

Journal of Superconductivity and Novel Magnetism - The Cr2FeAl inverse-based Heusler alloy nanoparticle was synthesized using mechanical alloy method. The as-prepared sample was annealed at various...     

TEM study of the decomposition of the Heusler alloy Cu2MnAl

Investigation of the equilibrium phase precipitation in the alloy Cu_2.00Mn_1.00 Al_1.00 performed previously by X-ray diffraction, magnesometry, SEM and resistometry was continued by means of TEM. It was found that the and-Mn precipitation mechanism was cellular in most cases. No T-phase precipitates were detected. The new results were compared with the previous ones and the temperature dependence of the-phase decomposition mechanism was explained in terms of the classical phase diagram of the Cu-Mn-Al system.     

Effect of Annealing Temperature on Structural and Magnetic Properties of Zn0.94Co0.05Cu0.01O

The doped ZnO system Zn_0.94Co_0.05Cu_0.01O (ZCCO) was prepared as a nano-polycrystalline by a simple sol–gel process, then air annealed at different temperatures. Applying X-ray diffraction (XRD) and the Rietveld method, structural analysis showed that Co and Cu replace Zn substitutionally yielding ZCCO single phase. The refined u-fractional coordinate of Zn increases monotonically by an annealing temperature from 0.3546 at 500 °C reaching 0.3722 at 800 °C, very near from the ideal value 0.375. The Zn tetrahedrons become more symmetric and the distortion is gradually relieved by annealing up to 800 °C. Annealing at 900 °C introduces tetrahedron distortion in an opposite way. The zero field cooled (ZFC) and field cooled (FC) magnetization versus the temperature at different applied fields and the magnetization versus the applied field at different temperatures were carried out. The system exhibits a ferromagnetic behavior at room temperature. As the annealing temperature increases from 550 to 900 °C, the saturation magnetization at 300 K increases from 0.0507 to 0.1088 emu/g.     

张力退火感生各向异性对纳米晶合金磁性能的影响

对Fe_74.1Cu₁Nb₃Si₁₅B_6.9(%,原子分数)纳米晶合金进行连续张力退火,研究了张力退火感生各向异性对纳米晶合金磁性能的影响。结果表明,张力退火产生的感生各向异性常数(K_u)与退火张力(σ)满足线性关系。随着退火张力的增大合金在f =5 kHz和H=3 A/m测试点的有效磁导率(μ_e)先增大后减小,且随着磁场和频率的提高有效磁导率(μ_e)的衰减减小。退火张力为67 MPa时有效磁导率(μ_e)在磁场强度H为0~800 A/m和频率f为1 k~3 MHz范围内保持约800,表现出恒导磁特性。同时,合金的单位质量损耗(P_m)随着退火张力的增大而减小,当退火张力为67 MPa时损耗为68 W/kg (测试条件：B_m=300 mT,f =100 kHz),与无张力退火相比下降约67%。同时,通过磁光克尔效应观察到张力退火后合金内部形成垂直于张力方向的180°片形畴,随着退火张力的增大磁畴宽度减小且趋于一致,退火张力为67 MPa时片形畴的宽度约为85 μm。     

Heusler合金磁性纳米线的制备方法及磁性的研究进展

磁性纳米线发展至今,已在高密度垂直磁性存储器、传感器、生物医学、催化剂等领域得到广泛应用.其中,Heusler合金磁性纳米线(Heu-sler alloy magnetic nanowires,HAMNWs)因其优异的性能备受关注.然而,目前HAMNWs制备工艺尚未成熟,存在组分偏差、结构无序、形貌不均等问题,阻碍了其基本物理性质的研究和功能器件的应用设计.当前已有的HAMNWs制备方法包括扩散驱动退火法、模板辅助法、化学合成退火法、分子束外延法、静电纺丝法、电沉积法等,这些方法各有其优势和缺陷.其中,SBA-15模板辅助的化学合成退火法制备的HAMNWs组分精确、结构高度有序,但该模板与AAO模板相比,孔道均一性相对较差,导致纳米线形貌均一性和有序性较弱;分子束外延法可以实现纳米线以原子级精度生长,然而,其制备设备昂贵、操作复杂,难以推广普及;扩散驱动退火法主要针对二元核壳型HAMNWs,而对于三元HAMNWs,其适用难度较大;静电纺丝法对组分和结构的控制较好,但对纳米线的形貌均一性控制较弱,整体呈纤维状;电沉积法制备的纳米线形貌均一可控,但对于含有难共沉积元素的合金纳米线,其组分和结构控制都较差.本文综述了HAMNWs的制备方法,详细对比了各种方法的优缺点;重点针对直流、脉冲、交流电沉积法制备过程中不同的生长机理进行了讨论,并在此基础上分析了纳米线生长过程中各种因素的影响与调控.同时还对纳米线的基本物理性质和磁性参数进行了归纳总结,最后对未来HAMN-Ws的制备及应用发展进行了展望.     

基于第一性原理研究Heusler合金Fe2CuGa的结构和性能

采用基于密度泛函理论的第一性原理,系统研究了Heusler合金Fe2CuGa的结构、磁性、弹性性能和电子性质.计算结果表明:立方相的基态结构是铁磁态的Hg2CuTi结构.立方到四方的相变几乎是体积不变的,这是形状记忆合金的特性.奥氏体和马氏体的磁矩分别是4.48和4.56μB/f.u..另外,预测了Fe2CuGa的弹性系数.Fe2CuGa的立方结构在力学上是不稳定的而四方结构是稳定的.根据体模量和剪切模量的比值,发现Fe2CuGa在本质上是可延展的.利用态密度的方法解释了Fe2CuGa马氏体相变的来源.     

热处理对Tb0.27Dy0.73Fe2巨磁致伸缩薄膜性能的影响

本文研究了热处理对Tb0.27Dy 0.73Fe2薄膜磁性及巨磁致伸缩性能的影响.XRD分析表明制备态的Tb0.27Dy 0.73Fe2薄膜为非晶态,并且在450℃退火仍然保持非晶态,制备态的Tb0.27 Dy0.73Fe2薄膜显示垂直磁各向异性,在退火后向平行磁各向异性变化.热处理提高了Tb0.27Dy0.73Fe2薄膜在低磁场下的磁致伸缩特性.     

Effect of Annealing Temperature on the Microstructure and Magnetic Properties of MnGa Films

MnGa films are the promising magnetic recording materials and spintronic materials owing to their intrinsic properties, such as large magnetic anisotropy, high coercivity, moderate magnetization, and high spin polarization. In this paper, MnGa films with high coercivity and low surface roughness have been successfully fabricated onto MgO substrates by magnetron sputtering and post-annealing. Moreover, the effects of post-annealing temperature (T _a) on crystalline structure, surface morphology, and magnetic performances of MnGa films have also been investigated. It is found that the crystallization temperature for MnGa films is 400 ^°C. With increasing T _a, the crystallization degree enhances and an in-plane texture is formed. The grain size and surface roughness of MnGa films increase slowly when T _a is below 500 ^°C, but they exhibit a rapid rise when T _a is above 500 ^°C. As T _a increases, the coercivity (H _c) and remanence squareness ratio (S) for MnGa films improve monotonically, whereas saturation magnetization (M _s) increases firstly and then drops. The increases in H _c, S, and M _s with T _a are attributed to the grains’ growth and the improvement of crystallinity, and the decrease of M _s at higher T _a possibly is due to the partial oxidation of Mn.     

退火效应对非晶TbFeCo薄膜磁性能的影响

详细研究了退火效应对非晶TbFeCo薄膜磁滞回线的影响。 10 0℃退火表明 ,薄膜保留较大的垂直磁各向异性、矫顽力和很好的矩形比 ,磁致伸缩各向异性是引起矫顽力下降的主要原因。经 13 0℃退火显示 ,矫顽力和垂直磁各向异性明显下降 ,薄膜仍展示垂直于膜面的矫顽力和磁滞回线 ,但是薄膜显示一清晰的平面内磁各向异性。实验表明 ,矫顽力和垂直磁各向异性的大大降低只是与退火温度的升高有关 ,而长时间的退火并不能有效影响薄膜的磁性和矫顽力。     

Effect of Vacuum and O2 Annealing Treatments on Structural and Magnetic Properties of La0.5Ca0.5MnO3 Thin Films

La_0.5Ca_0.5MnO₃ films with a nominal thickness of 80 nm were epitaxially grown on (001) SrTiO₃ and SrLaAlO₄ substrates by the pulsed laser deposition technique. The magnetic moment of the films was observed to depend strongly on the oxygen stoichiometry, tuned by heat treatments in vacuum and O₂ environments. A distinctly larger out-of-plane lattice parameter was measured for the vacuum-annealed films due to transformation of some Mn⁴⁺ ions to Mn³⁺. Both the variations in the magnetic moment and out-of-plane lattice parameter during vacuum annealing can be recovered by subsequent heat treatments in O₂ environment. In this study, it is shown that the enhancement of the magnetic moment via O₂ annealing is considerably less prominent than the respective improvement obtained by the application of compressive epitaxial strain.     

Surface Morphology, Structural and Magnetic Properties of Electrodeposited NiFeCu/Cu Films

The magnetic and structural properties of the NiFeCu/Cu films electrodeposited on polycrystalline titanium (Ti) substrates and their characterizations were studied. The structural analysis by X-ray diffraction (XRD) has revealed that all films have face-centred cubic (FCC) structure. On the other hand, the XRD analysis showed that the degree of (111) texture is dependent on the Cu content within the film. The composition analysis was carried out by energy-dispersive X-ray spectroscopy (EDX). The result of EDX indicated that the Cu content within the film increases with increasing of non-magnetic Cu layer thickness. The hysteresis loops of the films measured by vibrating sample magnetometer (VSM) showed that all films have a small coercivity typical for soft magnetic materials. The surface morphological structure of the films was investigated by atomic force microscopy (AFM). AFM images indicated that all films have main grains (globular islands) and smaller secondary grains on the main grains with different sizes. The differences observed in the magnetic properties of the films were attributed to the Cu content within the films.     

The Influence of KrF Excimer Laser Annealing on Magnetic and Structural Properties of FePt/PtIr Thin Films

A series of 60-nm FePt thin films were deposited by RF magnetron sputtering system on Si/SiO₂ substrate. Platinum–iridium alloy was deposited as a buffer film between the FePt thin film and Si/SiO₂ substrate. These films were annealed by KrF excimer laser annealing with 248 nm of wavelength. The number of laser pulses which were applied on the film was varied from 3 to 20. The A₁ to L₁₀ phase transformation of FePt was confirmed by X-ray diffraction. Three pulses of laser were not sufficient for A₁ to L₁₀ phase transformation. A maximum order parameter of 0.91 was obtained after applying 18 pulses of laser. The roughness of films changed in different pulses, and the films were in the best condition after applying 18 pulses; the roughness was 3.51 nm and its morphology that was observed from AFM was 129 nm. The maximum coercivity was 0.61 MA/m. The coercivity increased with the application of different pulses of laser. Increasing coercivity to the maximum value of 0.61 MA/m related to grain growth. Coercivity of samples in 3, 6, 9, 12, 18, and 20 pulses was 0.24, 0.402, 0.488, 0.522, 0.64, and 0.6 MA/m respectively. Determining the grain growth under condition of annealing was done by field emission scanning electron microscopy (FESEM). Growth of all specimens was calculated with imager software. Grain size in as deposited and 3, 6, 9, 12, and 18 pulses of laser was 15, 20, 29, 44, 47, and 59 respectively.     

退火对Y2O3薄膜结构和电学性能的影响

采用射频磁控反应溅射法,成功地在n-Si衬底上制备了高k栅介质Y2O3薄膜.对薄膜在不同温度退火后的结构、成分和电学性能进行了分析研究.结果表明,沉积态薄膜为非晶态,退火后薄膜开始晶化;沉积态薄膜中Y和O元素的原子浓度比基本符合化学计量比;薄膜具有较低的漏电流,退火后薄膜的漏电流降低.高频C-V曲线表明,退火后由于界面层的生长导致积聚电容减小.     

Annealing Effect in GaDyN on Optical and Magnetic Properties

The annealing effect on the optical and magnetic properties of the GaDyN layers was studied. The PL intensities of yellow and green bands as well as the intra-4f orbital transition of Dy³⁺ ions were found to decrease for the samples annealed at 900 and 1000 °C. It is supposed that the intra-4f orbital transition is related to the broad peak luminescence coming from defects. Increasing the annealing temperature, the magnetization becomes smaller. It is considerable that the number of electrons coming from defects was reduced by the annealing treatments and that the ferromagnetism in GaDyN is attributed as carrier induced ferromagnetism.     

Effects of Magnetic Annealing on Structure and Magnetic Properties of L10-FePt/Ag Films

The structural and magnetic properties of L1₀-FePt/Ag films were studied by X-ray diffraction and a vibrating sample magnetometer. The FeAg/Pt films were obtained by depositing FeAg thin films on thermally oxidized Si (001) substrates via magnetron sputtering and Pt layers on their surface after annealing FeAg thin films at 400 °C with and without an out-of-plane magnetic field of 10 kOe. These films were further annealed at various temperatures to obtain L1₀-FePt phase. The results indicated that the pre-annealing of FeAg thin films under 10 kOe magnetic field caused (001) orientation of Fe particles, and the deposition of Pt layer on such orientated underlayers reduced the ordering temperature of FePt in FeAg/Pt films, realizing the L1₀-FePt phase at 400 °C. The higher coercivity and ordering degree were also observed in the samples, compared with those pre-annealed without magnetic field at the same annealing condition.     

溅射FeSiAl合金薄膜的结构及软磁性能

Ｓｅｎｄｕｓｔ合金是制做薄膜磁头和ＭＩＧ磁头的理想材料，本工作用射频溅射法了备了Ｓｅｎｄｕｓｔ成分的ＦｅＳｉＡｌｗ合金薄膜，研究了制备对膜结构和软磁性能的影响，并对其机理进行了讨论。