铝纳米晶的低温导电特性研究

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T~4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.     

氢对非晶态Y5Ni95合金膜的磁性和电子输运性质的影响

采用电解法实现了非晶态Y,Ni₉₅合金的加氢。在1.5—400K温度范围内测量了a-Y,Ni₉₅H_x(x=0—15.1)合金的磁矩、电阻率和霍耳电阻率随氢含量的变化关系。结果指出,随氢含量增加,样品的0K磁矩、居里温度和电阻率温度系数显著下降,而高场磁化率、电阻率和反常霍耳系数则迅速增加。借助现行的理论对加氢引起的上述影响进行了简要的讨论。 关键词：     

FeCo基纳米晶合金高温交换耦合作用机理

研究了500和600℃真空退火后的纳米晶Fe_38.4Co₄₀Si₉B₉Nb_2.6Cu合金初始磁导率随温度的变化规律,发现较高温度(600℃)退火的FeCo基纳米晶合金,在非晶相居里温度以上较宽温度范围内磁导率没有明显的衰减,这是在双相纳米晶合金中观察到的一种新现象,其磁特性不同于Fe基纳米晶合金.为了探明这种现象的起源,估算了与剩余非晶相同成分的非晶合金的居里温度及纳米晶粒间发生交换耦合作用的参数 关键词： 交换耦合作用 非晶相居里温度 交换耦合穿透深度     

Cr-Al-V合金的电输运和热膨胀

本文报道了Cr97.02Al2 98和掺钒的(Cr98.26Al1.4)98 72V1.28、(Cr96.04Al3.96)98.69V1.31合金在10～450 K温区的电阻率和热膨胀系数随温度的变化.随着温度降低,Cr97.02Al2.98合金经历了顺磁-公度自旋密度波(CSDW)-非公度自旋密度波(ISDW)的转变.Neel温度以下电阻率出现上升趋势,与SDW反铁磁能隙的逐渐打开有关.热膨胀-温度曲线在Neel温度附近呈现一个明显的跳跃行为,是磁转变相关的磁体效应.低于CSDW-ISDW转变温度,电阻率的增大是由于磁散射在低温下增强.用公式p=P0 AlnT BT2 CTδ对三个合金10～80 K温区内电阻率-温度曲线的拟合结果表明,随着钒掺杂的增加,磁散射和s～d电子散射减小.Cr97.02Al2.98合金中掺入少量钒就能压制SDW.     

巨磁电阻锰氧化物材料的低温电阻率行为的研究

对巨磁电阻锰氧化物材料La2/3Ca1/3MnO3/YSZ(钇稳定氧化锆)(LCMO/YSZ)系列样品低温下电阻率行为进行研究,低温下电阻率行为一般是ρ=ρ0 ATa BTb的形式,其中ρ0为剩余电阻率,a=2或3/2,b=5或9/2.T2代表电子-电子散射项,T3/2代表被无序自旋玻璃散射的电子项,T6代表电子.声子散射项,Tθ/2们代表电子-双磁子散射项.在此指出b=5是合理的,代表电子-声子散射项.     

三维Al掺ZnO薄膜的低温电子散射机制北大核心CSCD

本文系统研究了厚度约1μm的Al掺ZnO(AZO)薄膜的低温电子散射机制.研究发现,薄膜在较高温区的电阻温度系数为正值,且载流子浓度在2~300K范围内不随温度而改变,表明薄膜具有简并半导体的电输运性质.通过测量薄膜在4~35K范围不同温度下的磁电阻,获得了低温下退相干散射率与温度的关系.与现有非弹性散射理论比较发现,仅由电子-声子散射并不能解释AZO薄膜低温下非弹性散射率与温度的依赖关系,除电子-声子散射外,必须同时考虑小能量转移电子-电子散射的贡献,这与薄膜较低的载流子浓度相关(我们的薄膜载流子浓度低于8×1020 cm^(-3)).我们的结果一方面表明电子-声子散射和电子-电子散射可以在三维无序导体中并存,另一方面从实验上定量地验证了关于电子-声子散射率与小能量转移电子-电子散射率的理论.     

三维Al掺ZnO薄膜的低温电子散射机制

本文系统研究了厚度约1μm的Al掺ZnO(AZO)薄膜的低温电子散射机制.研究发现,薄膜在较高温区的电阻温度系数为正值,且载流子浓度在2~300K范围内不随温度而改变,表明薄膜具有简并半导体的电输运性质.通过测量薄膜在4~35K范围不同温度下的磁电阻,获得了低温下退相干散射率与温度的关系.与现有非弹性散射理论比较发现,仅由电子-声子散射并不能解释AZO薄膜低温下非弹性散射率与温度的依赖关系,除电子-声子散射外,必须同时考虑小能量转移电子-电子散射的贡献,这与薄膜较低的载流子浓度相关(我们的薄膜载流子浓度低于8×1020 cm~(-3)).我们的结果一方面表明电子-声子散射和电子-电子散射可以在三维无序导体中并存,另一方面从实验上定量地验证了关于电子-声子散射率与小能量转移电子-电子散射率的理论.     

非晶态Fe_(87-x)Si_xB_(13)合金的磁化强度、电阻与温度的关系

本文研究了非晶态Fe_(87-x)Si_xB_(13)(x=0,9.6,14.5)合金的饱和磁化强度、电阻率与温度的关系。得到样品的居里温度T_C和晶化温度T_(cr)随Si含量的增加而明显提高。低温下的热磁关系符合布洛赫的T~(3/2)定律,计算出自旋波劲度系数D从x=0时的62meV·A~2增加到x=14.5时的111meV·A~2。从D值和Handrich理论分别推算出表示交换积分涨落的δ=<△J>~(1/2)/值相近。三个样品在低温区都出现电阻率的极小值,电阻率极小值的温度T_(min)从x=0时的10.5K增加到x=14.5时的24.6K。在T_(min)≤T≤130K和室温附近,电阻率分别与T~2和T成线性关系。用推广的Ziman理论讨论样品的电阻率与温度的关系。     

零磁场下La2/3（Ca0.60Ba0.40）1/3Mn1-xVxO3的电输运特性研究

采用溶胶-凝胶法制备了系列多晶CMR材料La2/3(Cao 60Bao.40)1/3Mn1-xVXO3,(x:0%、1%、5%、7%、10%、15%、20%).在零场下、77～350 K温度范围内测量了其电阻率随温度的变化关系,测量了该温度范围内0.1 T磁场下磁化强度随温度的变化关系.采用小极化子绝热跃迁模型P=aTexp(E/kT)对样品的电导特性进行拟合研究.结果发现,高温区电阻率随温度的变化很好地满足小极化子绝热跃迁模型;同时,采用单磁子散射模型对样品低温区的电输运曲线进行拟合,结果发现所有样品低温区的p～T关系同样都很好地满足单磁子散射公式P=po AT2严.由拟合结果分析了样品高温区的输运行为主要来源于小极化子的影响,而低温区电导特性主要来源于单磁子散射.     

非晶态Fe86M4Zr10合金的磁性和电性

本文研究了非晶态Fe₈₆M₄Zr₁₀(M=V,Cr,Mn,Fe,CO,Ni,Cu,B,Si)合金的基本磁性和低温电性,讨论了不同元素M的掺杂对FeZr合金居里温度和磁矩的影响,并用相干交换散射模型解释了样品在居里温度附近出现的电阻率极小。 关键词：     

Correlation between electron state density change and the electrical resistivity and magnetic permeability changes in the nanostructured powder of the NiMo alloy

The nanostructured powders of the Ni_95.4Mo_4.6 and Ni₉₉Mo₁ alloys (average crystallite dimensions of 14 and 21 nm) were obtained by the electrochemical deposition from ammonium solutions of nickel and molybdenum salts. The method of differential scanning calorimetry (DSC) and measurement of temperature dependence of the powder's electrical resistivity, magnetic permeability and the thermoelectromotive force were employed to examine structural changes of the powders. The nanocrystalline alloys Ni_95.4Mo_4.6 and Ni₉₉Mo₁ were stable up to about 460 K. The thermal stabilization of the alloys takes place within the temperature interval of 460–570 K. As a result of this process, a decrease in the electrical resistivity and increases in magnetic permeability as well as electron state density in the proximity of the Fermi level are observed. The crystallization temperature depends upon the current density of powder formation. The nanocrystalline alloy Ni_95.4Mo_4.6 obtained at j=70 mA cm⁻² becomes crystallized in the temperature range between 650 and 840 K, while the Ni₉₉Mo₁ alloy obtained at j=180 mA cm⁻² crystallizes in the 580–950 K temperature interval. The electrical resistivity and magnetic permeability of the nanocrystalline alloy decreased while the alloy's electron state density near the Fermi level increased after the process of crystallization took place. The electrical resistivity decrease recorded during the structural changes was due to an increase in the electron state density in the proximity of the Fermi level, as well as to an increase in the mean free path of the conducting electrons.     

深过冷液态Al-Ni合金中枝晶与共晶生长机理

在自由落体条件下实现了液态Al-4 wt.%Ni亚共晶、Al-5.69 wt.%Ni共晶和Al-8 wt.%Ni过共晶合金的深过冷与快速凝固. 计算表明, (Al+Al₃Ni)规则纤维状共晶的共生区是4.8–15 wt.%Ni成分范围内不闭合区域, 且强烈偏向Al₃Ni相一侧. 实验发现, 随液滴直径的减小, 合金熔体冷却速率和过冷度增大, (Al)和Al₃Ni相枝晶与其共晶的竞争生长引发了Al-Ni 共晶型合金微观组织演化. 在快速凝固过程中, Al-4 wt.%Ni亚共晶合金发生完全溶质截留效应, 从而形成亚稳单相固溶体. 当过冷度超过58K时, Al-5.69 wt.%Ni 共晶合金呈现从纤维状共晶向初生(Al) 枝晶为主的亚共晶组织演变. 若过冷度连续增大, Al-8 wt.%Ni过共晶合金可以形成全部纤维状共晶组织, 并且最终演变为粒状共晶.     

电阻率与强度性能的关联及铜合金性能分区

铜合金以低电阻率为特征,由于电阻率与强度存在着共同的微观结构机理,两者往往协同变化,而导致难以对合金进行性能的全面评估和选材.本文以Cu-Ni-Mo合金作为研究对象,以团簇结构[Mo_1-Ni_(12)]构建固溶体的近程序结构模型,解析了电阻率和强度依赖于成分的定量变化规律,并定义了拉伸强度/电阻率的值为代表合金本质特性的"强阻比",得到了完全固溶态Cu-Ni-Mo合金的强阻比为7×10~8MPa/?·m,完全析出态的强阻比为(310—490)×10~8MPa/?·m.进而应用强阻比对常用铜合金进行了性能分区,给出铜合金材料选材的依据,得出了基于Cu-(Cr, Zr, Mg, Ag, Cd)等二元基础体系的铜合金适用于高强高导应用,而基于Cu-(Be, Ni, Sn, Fe, Zn, Ti, Al)等为基础二元体系的铜合金不能实现高强高导.该强阻比为310的特征性能分界线的发现为合金性能的全面评估提供了量化依据,可指导高强高导铜合金的选材和研发.     

Structural, magnetic and transport properties of NiFeχAg(1−χ) heterogeneous alloys

We carried out a comprehensive study of structural, magnetic and electrotransport properties of as-deposited and annealed (Ni₈₀Fe₂₀)_χAg(_1−χ) heterogenous alloys prepared by sputtering. The NiFe atomic concentration was varied between 15% and 40%. These alloys consist of small magnetic particles (Ni₈₀Fe₂₀) embedded in a nonmagnetic matrix (Ag). The structures of these alloys were investigated by X-ray diffraction, scanning electron microscopy and high-resolution cross-section transmission electron microscopy. The magnetic measurements were made using SQUID magnetometry and ferromagnetic resonance. Magnetoresistance was measured with a conventional four-point probe between 1.5 K and room temperature in field range 0–6T. Three contributions to the magnetoresistance of these granular alloys have been clearly identified: the spin-valve (or giant) magnetoresistance as in multilayers, scattering on magnetic fluctuations (as in any ferromagnetic metal around its magnetic ordering temperature), and anisotropic magnetoresistance. These three contributions have their own dependences on the size of the magnetic particles, on the degree of intermixing between Ni₈₀Fe₂₀ and Ag, and on temperature. We discuss the different shapes and amplitudes of magnetoresistance versus Ni₈₀Fe₂₀ concentration or temperature and their evolution upon annealing in terms of the relative roles of these three contributions. The magnetoresistance in multilayers (current in-plane or perpendicular to the plane) and granular alloys are also compared.     

Ga含量对Mn2-xNiGa1+x结构和磁性的影响

系统研究了铁磁性形状记忆合金Mn_{2 -x}NiGa_1+x的结构、磁性和有序化转变. 研究表明: 随着Ga含量的增加, Mn_{2 -x}NiGa_1+x的母相结构由Hg₂CuTi 型逐渐转变到Cu₂MnAl型Heusler结构. 母相的晶格常数先增加后降低, 当x=0.3时达到最大值. 0.3 ≤x ≤0.8时, 材料除呈现Heusler结构的主相之外, 还出现了Ni₂In型六角相. 过渡金属中3d电子之间交换相互作用的减弱, 导致Mn_2-xNiGa_1+x主相的居里温度由Mn₂NiGa的590 K逐渐降低至Ga₂MnNi的220 K左右; 当x=0.6–0.8时, Ni₂In型六角相的居里温度与主相的居里温度出现分离. Ga对Mn的替代引起合金中原子间耦合作用的变化, 导致低温下Mn_{2 -x}NiGa_1+x的饱和磁化强度先增加后降低, 即x≤0.4时呈上升趋势, x>0.4时急剧下降. 差热分析结果显示, 随着x从0增加到1, 样品熔化温度逐渐降低, B2相到Heusler相的转变温度先降低后增加.     

Magnetovolume effects in transition metal alloys near the critical composition for ferromagnetism

Results of magnetovolume studies are presented on intermetallic compounds and binary alloys with weakly ferromagnetic properties of the following compositions: Ni₃Al, ( )₃Ga, Ti(Fe, Co), (Ti, Al)Co, Ni-Pt and Pd-Ni. Data for the pressure dependence of the spontaneous magnetization at 4.2 K and the shift of the Curie temperature with pressure follow roughly the realtions that can be derived in the model for weak itinerant ferromagnetism in most of the investigated systems. Invar-type of anomalies in the thermal expansion have already been observed in several cases. Experimental values for the magnetovolume parameter are derived and compared with theoretical predictions in the Stoner model.     

非晶Ni-P合金的晶化相

利用电镜双倾台倾转Ni₁₂P₅晶体以及对Vafaei-Makhsoos发表的数据的分析,证实了由他所提出的三个新的Ni₃P相并不存在。从而澄清了非晶Ni-P合金在加热过程中总共有七个晶化相析出:α=5.48?的面心立方亚稳相α,由此相转变生成的六角多型体α₁,α₂,α₃亚稳相,体心四方Ni₁₂P₅相,体心四方Ni₃P相及Ni固溶体。 关键词：     

Quantitative determination of anti-structured defects applied to alloys of a wide chemical range

Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure.Component distribution Ni_(75)Al_xV_(25-x) alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition,precipitate order,precipitate type,and phase stability.The Ni_(75)Al_xV_(25-x) alloys undergo single Ni_3V(stage Ⅰ),dual Ni_3Al and Ni_3V(stage Ⅱ with Ni_3V prior;and stage Ⅲ with Ni_3Al prior),and single Ni_3Al(stage Ⅳ) with enhanced aluminum level.For Ni_3V phase,anti-structured defects(V_(Ni1),Niy,except V_(Ni2)) and substitution defects(Al_(Ni1),Al_(Ni2),Al_v) exhibit a positive correlation to aluminum in stage I,the positive trend becomes to negative correlation or smooth during stage Ⅱ.For Ni_3 Al phase,anti-structured defects(Al_(Ni),Ni_(Al)) and substitution defects(V_(Ni),V_(Al)) have a positive correlation to aluminum in stage Ⅱ,but Ni_(Al) goes down since stage Ⅲ and lasts to stage Ⅳ.V_(Ni) and V_(Al) fluctuate when Ni_3Al precipitates prior,but go down drastically in stageⅣ.Precipitate type conversion of single Ni_3V/dual(Ni_3V+Ni_3Al) affects Ni_3V defects,while dual(Ni_3V+Ni_3Al)/single Ni_3 Al has little effect on Ni_3Al defects.Precipitate order swap occurred in the dual phase region affects on Ni_3Al defects but not on Ni_3V.     

Temperature dependence of the electrical resistivity of amorphous Co80−xErxB20 alloys

The temperature dependence of the electrical resistivity of amorphous Co_80−xEr_xB₂₀ alloys with x=0, 3.9, 7.5 and 8.6 prepared by melt spinning in pure argon atmosphere was studied. All amorphous alloys investigated here are found to exhibit a resistivity minimum at low temperature. The electrical resistivity exhibits logarithmic temperature dependence below the temperature of resistivity minimum T_min. In addition, the resistivity shows quadratic temperature behavior in the interval T_min<T<77 K. At high temperature, the electrical resistivity was discussed by the extended Ziman theory. For the whole series of alloys, the composition dependence of the temperature coefficient of electrical resistivity shows a change in structural short range occurring in the composition range 8–9 at%.