磁致伸缩/压电层叠复合材料磁电效应分析

采用有限元分析软件COMSOL5.0建立了三维悬臂梁模型,分析了磁致伸缩/压电/磁致伸缩叠层复合材料的磁电系数α_(ME),并就几何参数对复合结构磁电系数的影响进行了优化分析.首先,利用稳态求解器研究了磁电层状复合结构内部的应力、应变、位移以及电势分布情况,利用瞬态求解分析了磁电复合结构各变量动态分布规律;其次,应用小信号频域分析研究了该结构的谐振频率以及在不同偏置磁场对输出电压的影响,结果表明,随着直流偏置磁场的增加,输出电压逐渐减小.改变复合材料不同层的厚度,分析了磁电层与压电层厚度比t_m/t_p对磁电系数的影响,结果表明,随着厚度比增加,α_(ME)逐渐增大,其增加速率逐渐减小;最后,分析了磁电系数α_(ME)随复合结构面积、长宽比的变化情况.分析表明,α_(ME)随磁电复合结构面积的增加逐渐增加,其增加速率逐渐减小;当磁电复合结构面积恒定时,其磁电系数随长宽比L/W增加表现出先增加后减小的趋势,存在最优值.     

Large tunable FMR frequency shift by magnetoelectric coupling in oblique-sputtered Fe_(52.5)Co_(22.5)B_(25.0)/PZN-PT multiferroic heterostructure

In this study, we observe a strong inverse magnetoelectric coupling in Fe_(52.5)Co_(22.5)B_(25.0)/PZN-PT multiferroic heterostructure, which produces large electric field(E-field) tunability of microwave magnetic properties. With the increase of the E-field from 0 to 8 kV/cm, the magnetic anisotropy field Heffis dramatically enhanced from 169 to 600 Oe, which further leads to a significant enhancement of ferromagnetic resonance frequency from 4.57 to 8.73 GHz under zero bias magnetic field, and a simultaneous decrease of the damping constant α from 0.021 to 0.0186. These features demonstrate that this multiferroic composite is a promising candidate for fabricating E-field tunable microwave components.     

Electrical and dielectric characterization of Au/ZnO/n-Si device depending frequency and voltage

Au/Zn O/n-type Si device is obtained using atomic layer deposition(ALD) for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state(Nss), barrier height(Φb), series resistance(Rs), donor concentration(Nd), and dielectric characterization depending on frequency or voltage. These parameters are acquired by use of impedance spectroscopy measurements at frequencies ranging from 10 k Hz to 1 MHz and the direct current(DC) bias voltages in a range from-2 V to +2 V at room temperature are used. The main electrical parameters and dielectric parameters,such as dielectric constant(ε"), dielectric loss(ε"), loss tangent(tan δ), the real and imaginary parts of electric modulus(M and M), and alternating current(AC) electrical conductivity(σ) are affected by changing voltage and frequency. The characterizations show that some main electrical parameters usually decrease with increasing frequency because charge carriers at surface states have not enough time to fallow an external AC signal at high frequencies, and all dielectric parameters strongly depend on the voltage and frequency especially in the depletion and accumulation regions. Consequently, it can be concluded that interfacial polarization and interface charges can easily follow AC signal at low frequencies.     

Magnetic dynamics of two-dimensional itinerant ferromagnet Fe_3GeTe_2

Among the layered two-dimensional ferromagnetic materials(2 D FMs),due to a relatively high T_C,the van der Waals(vdW) Fe_3 GeTe_2(FGT) crystal is of great importance for investigating its distinct magnetic properties.Here,we have carried out static and dynamic magnetization measurements of the FGT crystal with a Curie temperature TC ≈ 204 K.The M-H hysteresis loops with in-plane and out-of-plane orientations show that FGT has a strong perpendicular magnetic anisotropy with the easy axis along its c-axis.Moreover,we have calculated the uniaxial magnetic anisotropy constant(K_1)from the SQUID measurements.The dynamic magnetic properties of FGT have been probed by utilizing the high sensitivity electron-spin-resonance(ESR) spectrometer at cryogenic temperatures.Based on an approximation of single magnetic domain mode,the K_1 and the effective damping constant(α_(eff)) have also been determined from the out-of-plane angular dependence of ferromagnetic resonance(FMR) spectra obtained at the temperature range of 185 K to T_C.We have found large magnetic damping with the effective damping constant α_(eff) ～ 0.58 along with a broad linewidth(ΔH_(pp) 1000 Oe at 9.48 GHz,H ‖ c-axis).Our results provide useful dynamics information for the development of FGT-based spintronic devices.     

Enhancement of microwave absorption of nanocomposite BaFe_(12)O_(19)/α-Fe microfibers

Nanocomposite BaFe12O19/α-Fe microfibers with diameters of about 1-5 μm are prepared by the organic gelthermal selective reduction process. The binary phase of BaFe12O19 and α-Fe is formed after reduction of the precursor BaFe12O19/α-Fe2O3 microfibers at 350℃ for 1 h. These nanocomposite microfibers are fabricated from α-Fe (16-22 nm in diameter) and BaFe12O19 particles (36-42 nm in diameter) and basically exhibit a single-phase-like magnetization behavior, with a high saturation magnetization and coercive force arising from the exchange-coupling interactions of soft α-Fe and hard BaFe12O19 . The microwave absorption characteristics in a 2-18 GHz frequency range of the nanocomposite BaFe12O19/α-Fe microfibers are mainly influenced by their mass ratio of α-Fe/BaFe12O19 and specimen thickness. It is found that the nanocomposite BaFe12O19/α-Fe microfibers with a mass ratio of 1:6 and specimen thickness of 2.5 mm show an optimal reflection loss (RL) of 29.7 dB at 13.5 GHz and the bandwidth with RL exceeding 10 dB covers the whole Ku-band (12.4-18.0 GHz). This enhancement of microwave absorption can be attributed to the heterostructure of soft, nano, conducting α-Fe particles embedded in hard, nano, semiconducting barium ferrite, which improves the dipolar polarization, interfacial polarization, exchange-coupling interaction, and anisotropic energy in the nanocomposite BaFe12O19/α-Fe microfibers.     

Control of spins in a nano-sized magnet using electric-current

With the development of spintronics,spin-transfer torque control of magnetic properties receives considerable attention.In this paper the Landau-Lifshitz-Gilbert equation including the torque term is used to investigate the magnetic moment dynamics in the free layer of the ferromagnet/non-magnetic/ferromagnet(FM1/N/FM2) structures.It is found that the reverse critical time τ_c decreases with the current increasing.The critical time τ_c as a function of current for the perpendicular and parallel easy magnetic axes are the same.The critical time τ_c increases with the damping factor α increasing.In the case of large current the influence of the damping factor α is smaller,but in the case of little torque the critical time τ_c increases greatly with the damping increasing.The direction of the magnetization in the fixed layer influences the critical time,when the angle between the magnetization and the z direction changes from 0.1π to 0.4π,the critical time τ_c decreases from 26.7 to 15.6.     

PrNi$lt;sub$gt;2$lt;/sub$gt;的磁和磁热性能研究

在一些磁性材料内, 磁性离子间交换作用和磁性离子的自旋涨落对材料磁性有影响. 本文根据磁比热实验值确定了晶场参数后, 利用包含自旋涨落的交换作用有效场H_m= n₀ (1 + γ T + β e^{ω T})M, 计算了PrNi₂晶体晶场能级的Zeeman劈裂. 在温度为3.8 K ≤T≤ 30 K范围内, 计算了该晶体多晶磁矩随外磁场的变化, 以及外磁场H=5000 Oe时磁化率倒数随温度的变化, 计算结果和实验值符合较好. 当外磁场在0–50000 Oe时, 计算的该晶体的磁熵变与已有文献的理论结果相似. 计算结果说明, 提出的包含自旋涨落的交换作用有效场不仅适合亚铁磁性晶体, 而且也适合顺磁性晶体. 关键词： 2')" href="#">PrNi₂ 磁比热 交换作用有效场 磁矩 磁熵变     

PECVD分层结构对提高氢化非晶硅TFT迁移率的影响

为了进一步提高氢化非晶硅薄膜晶体管 (a-Si:H TFT) 的场效应电子迁移率, 研究了批量生产条件下对欧姆接触层和栅极绝缘层进行多层 制备, 不同的工艺参数对a-Si:H TFT场效应电子迁移率的影响. 研究表明随着对欧姆接触层 (n⁺层) 分层数的增加, 以及低速生长的栅极绝缘层 (GL层) 和高速生长的栅极绝缘层 (GH 层) 厚度比值提高, a-Si:H TFT的场效应迁移率得到提升. 当n⁺层分层数达到 3层, GL层和GH层厚度比值为4:11 时, 器件的场效应电子迁移率达到0.66 cm²/V·s, 比传统工艺提高了约一倍, 显著改善了a-Si:H TFT 的电学特性, 并在量产线上得到了验证. 关键词： 非晶硅薄膜晶体管 电子迁移率 欧姆接触层 栅极绝缘层     

硒化锑薄膜太阳电池的模拟与结构优化研究

采用wx-AMPS模拟软件对硒化锑(Sb_2Se_3)薄膜太阳电池进行建模仿真,将CdS, ZnO和Sn02的模型应用到Sb_2Se_3太阳电池的电子传输层中.结果显示,应用CdS和ZnO都能实现较高的器件性能,并发现电子传输层电子亲和势(Xe-ETL)的变化能够调节Sb_2Se_3太阳电池内部的电场分布,是影响器件性能的关键参数之一.过高或者过低的Xe-ETL都会使电池的填充因子降低,导致电池性能劣化.当Xe-ETL为4.2eV时,厚度为0.6μm的Sb_2Se_3太阳电池取得了最优的7.87%的转换效率.应用优化好的器件模型,在不考虑Sb_2Se_3层缺陷态的理想情况下,厚度为3μm的Sb_2Se_3太阳电池的转换效率可以达到16.55%(短路电流密度J_(SC)=34.88 mA/cm~2、开路电压V_(OC)=0.59 V、填充因子FF=80.40%).以上模拟结果表明,Sb_2Se_3薄膜太阳电池在简单的器件结构下就能够获得优异的光电性能,具有较高的应用潜力.     

二维圆盘颗粒体系声学行为的数值研究

数值测量了卸载过程中二维单分散圆盘颗粒系统的横波、纵波声速、声衰减系数、非线性系数随压强的变化以及声衰减系数随频率的变化.结果表明,二维(2D)圆盘颗粒体系的横波、纵波声速均随压强呈分段幂律标度:当压强P10~(-4)时,横波、纵波声速随压强的增大而减小;当P10~(-4)时,有v_t~P~(0.202),v_l~P~(0.338).进一步得到其剪切模量和体积模量的比值G/B也随压强呈幂律标度,G/B~P~(-0.502),暗示在低压强下,与三维(3D)球形颗粒体系类似,2D圆盘颗粒体系也处于L玻璃态.水平激励和垂直激励下2D圆盘颗粒系统的衰减系数随频率变化也呈现分段行为:当频率f0.05时,衰减系数不随f变化;当f0.05时,横波纵波的衰减系数α~f;当f0.35时,横波衰减系数α_T~f~2,纵波衰减系数α_L~f~(1.5).此外,竖直水平激励下的2D圆盘颗粒系统的非线性系数和衰减系数随压强也呈现与声速类似的分段规律:当P10~(-4)时,横波非线性系数β_T~P~(-0.230),其余都不随压强变化.当P10~(-4)时,两者均随压强增大呈幂律减小:β_T~P~(-0.703),β_L~P~(-0.684),α_T~P~(-0.099),α_L~P~(-0.105).进而得到2D圆盘颗粒系统中散射相关的特征长度?~*随压强呈幂律标度,当P10~(-4)时,?~*~P~(-0.595);当P10~(-4)时,?~*~P~(0.236).     

偏置电压对磁致伸缩/压电层合换能结构磁电性能影响

分析和测试了偏置电压调整时PZT5/Terfenol-D/PZT8层合换能结构磁电性能. 提出了一种磁致伸缩/压电层合磁电换能结构的一阶谐振频率控制方法. 通过改变压电驱动层的直流电压对磁电层合结构的预应变进行改变, 从而调整谐振频率. 分析偏置电压、 应变、 弹性模量、 谐振频率和谐振磁电电压系数之间关系. 分析表明: 在较小应变情况下, 控制电压几乎可以线性调节谐振频率, 而层合结构谐振磁电电压系数几乎与偏置电压无关. 实验研究验证: 理论与实验结果较好吻合. 在-170 V-+170 V的偏置电压时, 谐振频率可以几乎线性调整. 最大频率调整量达到1 kHz, 偏置电压对一阶纵振频率的控制率达到: 2.94 Hz/V. 在偏置磁场为0-225 Oe时, 谐振频率调整量与偏置磁场无关. 偏置磁场会改变谐振磁电电压系数, 在大于178 Oe静态磁场偏置时, 磁电电压系数最大, 达到1.65 V/Oe.     

Improvement in coercivity,thermal stability,and corrosion resistance of sintered Nd-Fe-B magnets with Dy_(80)Ga_(20) intergranular addition

To investigate the coercivity,corrosion resistance,and thermal stability of Nd-Fe-B magnets,their properties were investigated at room and high temperature before and after doping with Dy_(80)Ga_(20)(at.%) powder.The coercivity of the magnets increased from the undoped value of 12.72 kOe to a doped value of 21.44 kOe.A micro-structural analysis indicates that a well-developed core-shell structure forms in the magnets doped with Dy_(80)Ga_(20) powder.The improvement in magnetic properties is believed to be related to the refined and uniform matrix grains,continuous grain boundaries,and a hardened(Nd,Dy)_2Fe_(14)B shell surrounding the matrix grains.Additionally,the doped magnets exhibit an obvious improvement in thermal stability.For the magnets with added Dy_(80)Ga_(20) powder,the temperature coefficients of remanence(α) and coercivity(β) increased to-0.106%℃~(-1) and-0.60%℃~(-1) over the range 20-100 ℃,compared to temperature coefficients of-0.117%℃~(-1)(α) and-0.74%℃~(-1)(β) in the regular magnets without Dy_(80)Ga_(20) powder.The irreversible loss of magnetic flux(Hirr) was investigated at different temperatures.After being exposed to 150 ℃ for 2 h,the Hirr of magnets with 4 wt.%Dy_(80)Ga_(20) decreased by ~95%compared to that of the undoped magnets.The enhanced temperature coefficients and Hirr indicate improved thermal stability in the doped Nd-Fe-B magnets.The intergranular addition of Dy_(80)Ga_(20) also improved the corrosion resistance of the magnets because of the enhanced intergranular phase.In a corrosive atmosphere for 96 h,the mass loss of the sintered magnets with 4 wt.%Dy_(80)Ga_(20) was 2.68 mg/cm~2,less than 10%of that suffered by the undoped magnets(28.1 mg/cm~2).     

Effects of Mg substitution on the structural and magnetic properties of Co_(0.5)Ni_(0.5-x)Mg_xFe_2O_4 nanoparticle ferrites

In this study, nanocrystalline Co–Ni–Mg ferrite powders with composition Co_(0.5)Ni_(0.5-x)Mg_xFe_2O_4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co–Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction(XRD) analysis, Fourier transform infrared spectroscopy(FTIR), field emission scanning electron microscopy(FESEM), and vibrating sample magnetometry(VSM). The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of ~ 32 nm to ~ 36 nm. The lattice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2+substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from ~ 57.35 emu/g to~ 61.49 emu/g and ~ 603.26 Oe to~ 684.11 Oe(1 Oe = 79.5775 A·m-1), respectively. The higher values of magnetization Ms and Mr suggest that the optimum composition is Co_(0.5)N_(i0.4)Mg_(0.1)Fe_2O_4 that can be applied to high-density recording media and microwave devices.     

Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(Ga_xFe_(1-x))_(1.9) compounds

The magnetostriction, magnetization, and spin reorientation properties in Pr(Ga_xFe_(1-x))_(1.9) alloys have been investigated by high-precision x-ray diffraction(XRD) step scanning, magnetization, and Mo¨ssbauer spectra measurements. Ga substitution reduces the magnetostriction(λ_(||)) with magnetic field H ≥ 8 kOe(1 Oe = 1.33322×10~2 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations(SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mo¨ssbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature(T_(SR)) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(T_x Fe_(1-x))_(1.9)(T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction(EMD) or T_(SR) for developing an anisotropic compensation system.     

Co/Co3O4/PZT多铁复合薄膜的交换偏置效应及其磁电耦合特性

本文采用溶胶-凝胶工艺并结合脉冲激光沉积技术, 在Pt/Ti/SiO₂/Si衬底上制备了Co/Co₃O₄/PZT多铁复合薄膜. 对复合薄膜的微结构和组分进行了表征, 并系统研究了复合薄膜中的交换偏置效应及其对磁电耦合作用的影响. 研究结果表明, 复合薄膜在77 K具有明显的交换偏置效应, 交换偏置场达到80 Oe, 且交换偏置场及矫顽场均随温度降低而增大. 当温度降低到10 K时, 交换偏置场增至160 Oe. X射线光电子能谱(XPS)测试结果证实在Co和Co₃O₄界面处存在约5 nm厚的CoO层, 表明77 K下的交换偏置效应源自反铁磁的CoO层对Co的钉扎作用. 观察到复合薄膜的电容-温度曲线随着外加磁场大小和方向的改变而呈现出规律性的变化, 表明复合薄膜存在磁电耦合效应. 进一步研究发现, 在低温下复合薄膜呈现出各向异性的磁电容效应, 与磁场大小和方向密切相关. 复合薄膜的这种磁电耦合特性主要与复合体系的交换偏置效应及基于界面应力传递的磁电耦合作用有关, 本文对其中的物理机理进行了详细讨论与分析.     

First-principles calculation of the structural,electronic, elastic,and optical properties of sulfur-doping ε-GaSe crystal

The structural,electronic,mechanical properties,and frequency-dependent refractive indexes of GaSe_(1-x)S_x(x=0,0.25,and 1) are studied by using the first-principles pseudopotential method within density functional theory.The calculated results demonstrate the relationships between intralayer structure and elastic modulus in GaSe_(1-x)S_x(x=0,0.25,and 1).Doping of ε-GaSe with S strengthens the Ga-X bonds and increases its elastic moduli of C_(11) and C_(66).Born effective charge analysis provides an explanation for the modification of cleavage properties about the doping of e-GaSe with S.The calculated results of band gaps suggest that the distance between intralayer atom and substitution of S_(Se),rather than interlayer force,is a key factor influencing the electronic exciton energy of the layer semiconductor.The calculated refractive indexes indicate that the doping of ε-GaSe with S reduces its refractive index and increases its birefringence.     

硬X射线调制望远镜低能探测器量子效率标定

低能X射线望远镜是硬X射线调制望远镜卫星的主要载荷之一,探测器采用CCD236.探测器的量子效率会影响能谱拟合和绝对流量,有必要对其进行标定.利用~(55)Fe放射源,以硅漂移探测器为标准探测器,标定了CCD236在Mn-K_α(5.899 keV)和Mn-K_β(6.497 keV)能量点处的量子效率,此能段在Fe线附近,对X射线天文观测有重要价值.考虑探测器的分裂事例后,Mn-K_α和Mn-K_β处的量子效率分别为71%和62%.在-95—-30?C工作温度范围内,CCD量子效率与温度无关.利用CCD236的结构及实测的量子效率,不考虑沟阻影响,得到耗尽层厚度为38μm.对CCD236施加不同的电压,其量子效率基本不变,表明其在两相驱动下高低电平的耗尽层厚度相等,进而说明CCD236一直工作在深耗尽状态,其耗尽层到了外延层和衬底层边界,已达最大值.     

含R2NCS2配体的Mo(W)-Cu-S簇合物的1H NMR研究

报道了十一个含R₂NCS₂配体的Mo (W)-Cu-S簇合物的,¹H NMR研究结果,表明异金属簇合物导致配体中α-H的NMR谱线严重加宽.对谱线的位移,化合物的结构及配位键键长L_Cu-s之间的关系也作了讨论.     

NFX(X=-1,0,+1)分子离子基态的结构与势能函数

用密度泛函理论的B3LYP方法,分别以6-311++g(df,3pd),6-311g(3d,3p)和6-311++g(3df,3pd)为基函数对NF分子、NF⁺和NF^-离子基态进行几何优化和频率计算,并进行单点能扫描计算.用最小二乘法拟合得到NF^X(X=-1,0,+1)分子离子基态的Murrell-Sorbie势能函数.利用得到的解析势能函数计算出的NF分子和NF⁺离子基态光谱常数(B_e,α_e,ω_e,ω_eχ_e)与实验值符合很好.首次得到NF^-离子基态的光谱常数(B_e,α_e,ω_e,ω_eχ_e)和力常数(f₂,f₃,f₄),为NF-离子基态的后期研究提供理论参考.     

具有时滞反馈的非对称双稳系统中的振动共振研究

研究了具有时滞反馈的非对称双稳系统中的振动共振现象. 在绝热近似条件下, 应用快慢变量分离法得到系统响应振幅的解析表达式Q, 分析了时滞参数α和不对称参数r对振动共振现象的影响. 结果表明: 在Q-α平台上, α可以诱导响应幅值的极大值以输入高频信号和低频信号的周期出现. 不对称参数并不影响共振发生的位置, 但是能够增强响应幅值. 在Q-B (B为高频信号振幅)平台上, 共振发生的位置B_VR随着α呈现两种不同的周期关系, 且周期分别为输入高频信号和低频信号的周期. 在Q-Ω (Ω高频信号频率)平台上, 随着时滞参数的增大, 当B较小时, 在Ω的小值区间内, Q呈现出多重共振现象, 在Ω的大值区间, Q趋于定值.