Tb0.3Dy0.7Fe2合金的本构参数辨识方法研究

建立了一种简便的、适用于磁畴模型应用的Tb0.3Dy0.7Fe2合金本构参数辨识方法.针对Tb0.3Dy0.7Fe2合金磁畴模型中本构参数不明确且直接实验测试困难的问题,提出了一种数值计算与实验测试相结合的参数辨识方法.采用坐标变换与绘制自由能等势曲线相结合的方法,简化了载荷作用下Tb0.3Dy0.7Fe2合金内磁畴角度偏转的数值计算,研究了合金磁畴角度偏转模型的参数依赖性.在此基础上,结合简单的实验测试,建立了Tb0.3Dy0.7Fe2合金各向异性常数K1和K2、能量分布因子ω、晶轴取向分布的辨识及修正方法.该方法能够简单、快速地完成Tb0.3Dy0.7Fe2合金磁畴模型中本构参数的辨识,对完善磁致伸缩材料磁畴偏转的数值计算模型非常有意义.理论分析可为类磁致伸缩材料磁机耦合模型的建立、完善,以及材料本构参数的辨识、获取提供参考.     

A structural, magnetostrictive and M(o)ssbauer study of Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys

The effect of ⅢA metal and transition metal T substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe0.9T0.1)1.95 (T = Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys is the MgCu2-type cubic Laves phase structure for different substitution. The magnetostriction λs decrases greatly for the substitution of IIIA metal B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λs. It was also found that the effect of different substitutions on the spontaneous magnetostriction λ111 is distinct. The analysis of the Mossbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.     

Increase in the magnetostrictive susceptibility of Tb0.3Dy0.67Ho0.03Fe2−x Co x alloys upon substitution of cobalt for iron

This paper reports on the results of investigations into the concentration dependences of the magnetostrictive susceptibility, the magnetostriction, the magnetization, and the Curie temperature for Tb_0.3Dy_0.67Ho_0.03Fe_2?x Co _x alloys upon substitution of cobalt for iron. It is revealed that the temperature of the spin-reorientation transition shifts toward room temperature with an increase in the cobalt content in the range 0 ≤ x ≤ 1.3. Substitution of cobalt for iron in the alloys leads to a decrease in the contribution of the 3d transition metal sublattice to the magnetic anisotropy owing to the opposite signs of the single-ion anisotropy constants for iron and cobalt. The decrease observed in the magnetocrystalline anisotropy compensated in both rare-earth and 3d transition metal sublattices is responsible for the high magnetostrictive susceptibility of the studied compounds at a high cobalt content (x = 1.3) in the room-temperature range.     

Tb0.3Dy0.7(Fe1-xAlx)1.95合金的磁致伸缩、自旋重取向和穆斯堡尔谱研究

系统研究了室温下Tb0.3Dy0.7(Fe1-xAlx)1.95(x=0,0.05,0.1,0.15,0.2,0.25,0.3,0.35)合金中金属Al替代Fe对晶体结构、磁致伸缩、各向异性和自旋重取向的影响.结果发现,x<0.4时,Tb0.3Dy0.7(Fe1-xAlx)1.95完全保持MgCl2立方Laves相结构,晶格常量a随Al含量x的增加而增大.磁致伸缩测量发现,随着替代量x的增多磁致伸缩减小,x>0.15时超磁致伸缩效应消失;x<0.15时磁致伸缩在低场下(H≤4kA/m)有小幅增加,高场下迅速减小,而且易趋于饱和,说明添加少量Al有助于减小磁晶各向异性.内禀磁致伸缩λ111随Al替代量x的增加大幅度降低.对于0≤x<0.15,穆斯堡尔效应表明,随Al含量的增加Tb0.3Dy0.7(Fe1-xAlx)1.95合金中发生了自旋重取向,易磁化方向经历了[111]→[u v 0]→[u v w]的转变.由相对磁化率随温度的变化关系可以看出,Al替代Fe使自旋重取向温度降低.当x=0.15时,Tb0.3Dy0.7(Fe1-xAlx)1.95合金中出现了少量非磁性相;x>0.15时,合金在室温下呈现顺磁性.     

La0.7Ca0.3MnO3/MgAl2O4复合样品的电输运特性

我们用传统的固相反应法制备了(La0.7Ca0.3MnO3)1-x(MgAl2O4)x复合样品.通过XRD分析发现在此系列复合样品中La0.7Ca0.3MnO3和MgAl2O4两相共存;电阻率温度关系分析表明MgAl2O4的引入没有改变母体相在温度TP1处本征的金属-绝缘体转变峰,但使复合样品在较低温度TP2处出现另外一个电阻率峰值.有趣的是,随着MgAl2O4掺量的增加,在低掺量时,TP2向低温偏移很快;但在高掺量时,TP2向低温偏移较慢.     

Structure, spin reorientation and M(o)ssbauer effect studies of Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb0.3Dy0.7(Fe1-xAlx)1.95 is the MgCu2-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb0.3Dy0.7(Fe1-xAlx)1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction ( inceases slightly in a low magnetic field (H ≤ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction (ζ)111 decreases greatly with x increasing. The analysis of the M(o)ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperture, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

Tb0.3 Dy0.7(Fe0.9 T0.1)1.95合金的结构、自旋重取向和穆斯堡尔谱

系统研究了室温下Tb0.3Dy0.7(Fe0.9T0.1195(过渡金属元素T=Mn,Fe,Co,B,Al,Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现,不同金属T替代Fe,Tb0.3Dy0.7(Fe009T0.11.95,合金具有相同的MgCu2型立方Laves相结构;Al,Ga替代使Tb0.3Dy0.7(Fe09T0.11.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴,即自旋重取向,B,Mn,Co替代未使易磁化轴发生明显转动;Al,Ga元素替代使超精细场Hhf略有下降,B,Mn替代对超精细场Hhf的影响不大,而Co元素替代使超精细场Hhf有较大增加;所有元素替代使同质异能移IS有所增加;B,Al,Ga和Mn替代使四极劈裂Qs增加,而Co替代使四极劈裂Qs下降.     

Tb0.3Dy0.7－xPrx(Fe0.9Al0.1)1.95合金的磁致伸缩、自旋重取向和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95 (x=0，0.1，0.2，0.25，0.3，0.35)合金中稀土元素Pr替代Dy对晶体结构、磁致伸缩、各向异性和自旋重取向的影响. 结果发现，x≤0.1时，Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95完全保持MgCl₂立方Laves相结构，0.1<x≤0.3，有杂相出现并且随Pr替代量逐渐增多；晶格常数a随Pr含量x的增加缓慢增大. 磁致伸缩测量发现，随着替代量x的增多磁致伸缩减小；x>0.2时超磁致伸缩效应消失. 然而，x=0.1时合金的磁致伸缩略大于没有替代的，而且磁致伸缩随磁场更易趋于饱和，说明Pr替代有助于降低磁晶各向异性. 内禀磁致伸缩λ₁₁₁随Pr替代量x的增加接近线性增加. 由相对磁化率随温度的变化关系可以看出，自旋重取向温度随Pr替代量的增多呈先增后降趋势，在x=0.1处出现极大值. 穆斯堡尔效应表明，随Pr含量的增加Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95合金中易磁化轴可能在{110}面上绕主对称轴作微小转动，发生自旋重取向. 与Al元素替代效应相比，Pr替代Dy对自旋重取向的影响相对较小.     

Magnetostriction of a single cubic laves phase compound Tb0.27Dy0.73Fe2

The magnetostriction of a single crystal cubic Laves phase compound Tb_0.27Dy_0.73Fe₂ is measured with the applied field (0–25 kOe) in the [111] direction in the temperature range between 80 and 300 K. Evidence is seen of a possible transition to the[uv0] easy axis phase during the spin re-orientation form [100] easy axis direction to the [110] easy axis direction.     

Moisture absorption characteristics and effects on mechanical properties of Kolon/epoxy composites

Para-aramid fibers (Kolon) are high performance polymeric fibers characterized by their high tenacity and impact resistance. They are used for the soft body armor structures in ballistics. In this study, the testing specimens were made from multilayered Kolon fabrics impregnated with epoxy resin where silicon carbide (SiC) microparticles or SiC nanofibers were added as reinforcement. The laminated composite samples were fabricated by hot compression and curing of epoxy resin.The tensile and impact strengths of the untreated specimens were compared with the ones that underwent water absorption in duration of 72 h (immersion or humidity) followed by desorption. The immersion of the specimens in water and exposure to high humidity (70%) were performed according to the ISO 62 standard while the tensile test was carried out in accordance with the ASTM D 3039 standard. In the end, the tensile test simulation of the laminated composite by using software Abaqus® was accomplished.     

Dy的高掺杂对La0.7Sr0.3MnO3体系磁电性质的影响

通过实验研究了La0.7-xDyxSr0.3MnO3(x=0.00,0.30,0.40,0.50,0.60,0.70)体系的M-T曲线,M-H曲线,ρ-T曲线和MR-T曲线. 实验结果表明:随着Dy掺杂的增加,体系从长程铁磁有序向自旋团簇玻璃态、反铁磁及亚铁磁状态转变. x=0.30样品的M-T曲线上在TN附近出现磁化强度尖峰,x=0.40时尖峰消失. 对x=0.50样品,ZFC的M-T曲线随温度增加出现一个谷,随后在TN处出现峰;而FC的M-T曲线在低温下呈现负磁矩. 对x=0.60和0.70样品,不论FC还是ZFC的M-T曲线都类似于x=0.50的ZFC的M-T曲线. 高掺杂时的输运性质在其磁背景下发生异常. 这些奇异现象用Nel的双格子模型并联合M-H回滞曲线给予很好地解释.     

Dy的高掺杂对La0.7Sr0.3MnO3体系磁电性质的影响

通过实验研究了La07-xDyxSr03MnO3(x=000，030，040，050，060，070)体系的M_T曲线，M_H曲线，ρ_T曲线和MR_T曲线. 实验结果表明：随着Dy掺杂的增加，体系从长程铁磁有序向自旋团簇玻璃态、反铁磁及 亚铁磁状态转变. x=030样品的M_T曲线上在TN附近出现磁化强度尖峰， x=040时尖峰消失. 对x=050样品，ZFC的M_T曲线随温度增加出现一个谷，随 后在TN处出现峰；而FC的M_T曲线在低温下呈现负磁矩. 对x=060和070 样品，不论FC还是ZFC的M_T曲线都类似于x=050的ZFC的M_T曲线. 高掺杂时的输 运性质在其磁背景下发生异常. 这些奇异现象用Nel的双格子模型并联合M_H回滞曲线 给予很好地解释. 关键词： 磁结构 输运行为 庞磁电阻效应     

Enhanced low-field-magnetoresistance and electro-magnetic behavior of La0.7Sr0.3MnO3/BaTiO3 composites

We report the structural, magentoresistance and electro-magnetic properties of ferromagnet–ferroelectric–type (1−x)La_0.7Sr_0.3MnO₃/xBaTiO₃ (with x=0.0%, 3.0%, 6.0%, 12%, 15.0% and 18.0%, in wt%) composites fabricated through a solid-state reaction method combined with a high energy milling method. The insulator–metal transition temperature shifts to a lower temperature and resistivity increases while the feromagnetic–paramagnetic transition temperature remains almost unchanged with the increase of BaTiO₃ content. Magnetoresistance of the composites at an applied magnetic field H=3 kOe is enhanced in the wide temperature ranges with the introduction of BaTiO₃, which could be explained by the enhanced spin polarized tunneling effect induced by the introduction of BaTiO₃. The low-field magnetoresistance of the composite is analyzed in the light of a phenomenological model based on the spin polarized tunneling at the grain boundaries. Furthermore, the temperature dependence of resistivity for this series has been best-fitted by using the adiabatic small polaron and variable range hopping models. These models may be used to explain effect of BTO on the electronic transport properties on high temperature paramagnetic insulating region.     

Magnetic properties and static-dynamic magnetostrictive characteristics for SmFe2/Fe exchange-coupled multilayers

Giant magnetostrictive SmFe₂/Fe exchange-coupled multilayers were fabricated by ion beam sputtering deposition on glass substrates. The effects of SmFe₂/Fe exchange coupling action and vacuum annealing on soft-magnetic property and static-dynamic magnetostrictive characteristics of SmFe₂/Fe multilayers were investigated. The results showed that the soft-magnetic, static-dynamic magnetostrictive characteristics were greatly improved by SmFe₂/Fe exchange coupling action and proper vacuum annealing treatment temperature. Compared with that of SmFe₂ single film, the coercivity in the direction of easy magnetization axis for SmFe₂/Fe exchange-coupled multilayers exhibited a greater decrease. Better soft-magnetic properties were achieved (H_c=2.54 kA/m, M_s=120.38 emu/g, and M_r/M_s=0.21) after vacuum annealing at certain temperature. The magnetostrictive coefficient for SmFe₂/Fe exchange-coupled multilayers was about 135 ppm at 16 kA/m magnetic field. At first order resonant frequency (99.2 Hz), the amplitude peak-peak value for the as-deposited SmFe₂/Fe exchange-coupled multilayers was 46 μm. After the vacuum annealing treatment at 250 °C, the amplitude peak-peak value increased to 650 μm.     

Magnetic and Superconducting Properties of the Heterogeneous Layered Structures V/Fe0.7V0.3/V/Fe0.7V0.3/Nb and Nb/Ni0.65(0.81)Cu0.35(0.19)

Journal of Experimental and Theoretical Physics - The heterogeneous ferromagnetic–superconducting layered heterostructures V/Fe0.7V0.3/V/Fe0.7V0.3/Nb and Nb/Ni0.65(0.81)Cu0.35(0.19), which...     

Thermal and mechanical properties and micro-mechanism of SiO2/epoxy nanodielectrics

In addition to electrical insulation properties, the thermal properties of nanodielectrics, such as glass transition temperature, thermal expansion coefficients, thermal conductivity, and mechanical properties, including Young's modulus, bulk modulus, and shear modulus, are also very important. This paper describes the molecular dynamics simulations of epoxy resin doped with SiO₂ nanoparticles and with SiO₂ nanoparticles that have been surface grafted with hexamethyldisilazane (HMDS) at 10% and 20% grafting rates. The results show that surface grafting can improve certain thermal and mechanical properties of the system. Our analysis indicates that the improved thermal performance occurs because the formation of thermal chains becomes easier after the surface grafting treatment. The improved mechanical properties originate from two causes. First, doping with SiO₂ nanoparticles inhibits the degree of movement of molecular chains in the system. Second, the surface grafting treatment weakens the molecular repulsion between SiO₂ and epoxy resin, and the van der Waals excluded region becomes thinner. Thus, the compatibility between SiO₂ nanoparticles and polymers is improved by the grafting treatment. The analysis method and conclusions in this paper provide guidance and reference for the future studies of the thermal and mechanical properties of nanodielectrics.     

Effect of silane/nano-silica on the mechanical properties of basalt fiber reinforced epoxy composites

The present study explains the role of surface modification of constituent materials on composite material performance. The influence of silane and nano-hybrid coatings on mechanical properties of basalt fibers and composite materials on their base was investigated. Infrared spectroscopy indicated that modification of basalt fiber surface and nano-SiO₂ was successfully applied. The surface modification leads to the significant increase in the tensile strength of basalt fibers compared to the non-coated fibers. The tensile strength of silane-treated fibers was established 23% higher than the non-coated fibers, indicating that silane plays a critical role in the strength retention of basalt fibers. Also it was pointed out that silane coupling agents can be used for the preparation of the nano-hybrid coating. Addition of SiO₂ nanoparticles into the fiber surface was incorporated to enhance the interfacial bonding of basalt fiber reinforced epoxy composite.     

Mechanical properties of epoxy resins and glass/epoxy composites at cryogenic temperatures

The mechanical properties of four modified-epoxy resin systems were investigated. Tensile properties (including strength, modulus, and elongation), notch toughness, impact strength, the coefficient of linear thermal contraction, and thermal-shock resistance were determined for cast-resin specimens at 75, ?320, and ?423°F. Inter-laminar shear strengths (Naval Ordnance Laboratory horizontal shear and short-span shear) were obtained for glass-filament-wound-composite specimens at the three temperatures.

The two systems with the best cryogenic properties were a hybridepoxy/polyurethane (resin 4A) and a highly modified bisphenol-A epoxy (resin 2). In choosing the optimum system, the same tests (except for notch toughness, impact strength, and short-span shear) were performed on filament-wound-composite specimens at the three temperatures. In these tests the performance of resin 4A was better than, or at least comparable to, that of resin 2.     

Transport properties of Pr0.7Ca0.3MnO3/Nb:SrTiO3 heterojunctions

Current–voltage (J–V) characteristics of epitaxial hetero-junctions composed of Pr_0.7Ca_0.3MnO₃ and Nb:SrTiO₃ were studied under forward and reversed bias conditions. Detailed analysis showed that the J–V characteristics of these heterojunctions can be well-fitted by the thermally-assisted tunnelling model. While the dielectric constant of Nb:SrTiO₃ extracted under the forward bias was about one order of magnitude smaller than that of bulk SrTiO₃, the value obtained under reverse bias was very close to that of the bulk SrTiO₃. The result can be explained by the existence of an interface layer on the Nb:SrTiO₃ substrate with a smaller effective dielectric constant. The current finding suggested that the properties of interface layer should be taken into account in order to accurately simulate the J–V characteristics of such heterojunctions.