Enhanced orbital magnetism in Fe(50)Pt(50) nanoparticles

X-ray absorption and magnetic circular dichroism spectra at both the Fe and Pt L(3,2) edges were measured on wet-chemically synthesized monodisperse Fe(50)Pt(50) particles with a mean diameter of 6.3 nm before and after complete removal of the organic ligands and the oxide shell covering the particles by soft hydrogen plasma resulting in a pure metallic state. After thermal treatment of the metallic particles, the coercive field increased by a factor of 6, the orbital magnetic moment at the Fe site increased by 330% and is reduced at the Pt site by 30%, while the effective spin moments did not change. A decrease of the frequency of oscillations in the extended x-ray absorption fine structure at the Pt L(3,2) edges provides evidence for crystallographic changes towards the L1(0) phase.     

分子束外延生长Fe/Fe_(50)Mn_(50)双层膜的交换偏置

利用表面磁光克尔效应和铁磁共振对分子束外延生长的Fe/Fe50Mn50双层膜的交换偏置场和矫顽力进行了研究,实验结果表明,当反铁磁层厚度小于5.5!nm时,不出现交换偏置,而当大于这一厚度时,出现交换偏置;大约在7!nm时,达到极大值.随着反铁磁层厚度的继续增大,偏置场和矫顽力随Fe50Mn50膜厚的增大而下降.铁磁共振实验结果表明样品的磁性存在单向各向异性.并对上述结果进行了讨论.     

Evidence for strain glass in the ferroelastic-martensitic system Ti(50-x)Ni(50+x)

We report here "strain glass," a new glassy phenomenon in ferroelastic-martensitic system of Ni-rich intermetallic Ti(50-x)Ni(50+x) (x > 1), where local strain is frozen in disordered configuration below a critical temperature Tg. The ac elastic modulus shows a minimum at Tg, which exhibits logarithmic frequency dependence following Vogel-Fulcher relationship, and the corresponding internal friction shows a frequency-dependent peak located at a lower temperature. In situ high-resolution transmission electron microscopy observations reveal uncorrelated nanoclusters of martensiticlike phase, randomly frozen in the otherwise untransformed parentlike matrix. Being parallel to spin glass and relaxor, strain glass may shed new light on the fundamental physics of glass and lead to the discovery of novel properties.     

Notch fatigue of Cu_(50)Zr_(50) metallic glasses under cyclic loading: molecular dynamics simulations

Molecular dynamics simulation is performed to simulate the tension–compression fatigue of notched metallic glasses(MGs), and the notch effect of MGs is explored. The notches will accelerate the accumulation of shear transition zones, leading to faster shear banding around the notches' root causing it to undergo severe plastic deformation. Furthermore, a qualitative investigation of the notched MGs demonstrates that fatigue life gradually becomes shorter with the increase in sharpness until it reaches a critical scale. The fatigue performance of blunt notches is stronger than that of sharp notches. Making the notches blunter can improve the fatigue life of MGs.     

Ni_(50)Al_(50)合金的液固转变及晶体生长过程的分子动力学模拟

采用分子动力学模拟技术研究了液态Ni50 Al50 合金在不同冷速下的凝固特点 ,模拟采用EAM作用势 ,计算了不同温度 ,不同冷速下Ni50 Al50 的偶分布函数。结果表明EAM作用势能很好地描述液态Ni50 Al50 的无序结构 ,在快速凝固条件下 ,液态Ni50 Al50 形成非晶 ,当冷速较慢时 ,液态Ni50 Al50 形成晶体 ,分析了不同冷速下体系的相变热力学及相变动力学特点。最后采用液固两层构型法 ,清楚地观察到Ni50 Al50 晶体生长的全过程。     

Coulomb energy differences in t = 1 mirror rotational bands in (50)Fe and (50)Cr

Gamma rays from the N = Z-2 nucleus (50)Fe have been observed, establishing the rotational ground state band up to the state J(pi) = 11+ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror (50)Cr, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the pf model space.     

Cross-section measurements and thermonuclear reaction rates for 50Ti(p, γ)51V and 50Ti(p,n)50V

The yields of γ-rays from the reactions ⁵⁰Ti(p, γ)⁵¹V and ⁵⁰Ti(p, p 'γ)⁵⁰Ti have been measured as a function of bombarding energy over the range 0.73–4.39 MeV and the yield of neutrons from the reaction ⁵⁰Ti(p, n)⁵⁰V has been measured from threshold to a bombarding energy of 4.39 MeV. Competition effects were observed in the γ-ray yields from the (p, γ) and (p, pγ) reactions at the threshold of the (p, n) reaction. The observed yields in all channels were lower by factors of order 3 than those predicted by statistical-model calculations based on global optical parameters and the competition observed in the (p, γ) yield at the opening of the neutron channel was approximately one half that predicted by the statistical-model calculations. These failures of the calculations are tentatively attributed to the neutron closed-shell nature of ⁵⁰Ti. Thermonuclear reaction rates for the (p, γ) and (p, n) reactions are calculated for the temperature range (0.6–5) × 10⁹ K which includes the range of temperatures of interest in nucleosynthesis calculations.     

Effect of Ni substitution on the formability and magnetic properties of Gd_(50)Co_(50) amorphous alloy

A small amount of Ni was added into the binary Gd_(50)Co_(50) amorphous alloy to replace Gd in order to obtain ternary Co_(50)Gd_(50-x)Ni_x(x = 1, 2, and 3) amorphous alloys. Compared to the binary Gd_(50)Co_(50) amorphous alloy, the Co_(50)Gd_(50-x)Ni_x amorphous alloys show an enhanced Curie temperature(T_C) with a weakened formability. The maximum magnetic entropy change(-?S_m~(peak)) of the Co_(50)Gd_(50-x)Ni_x amorphous alloys is found to decrease with the increasing T_C.The adiabatic temperature rise(?T_(ad)) of the Co_(50)Gd_(47)Ni_3 amorphous alloy is superior to that of the Fe-based metallic glasses at room temperature. The variation of the T_C and -?S_~(peak) of the Gd_(50)Co_(50) amorphous alloy with Ni addition, and the mechanism involved, were discussed.     

Intermediate width structures in the reaction50Ti(p,n)50V

The total (p, n) reaction cross section for⁵⁰Ti has been measured from threshold upto about 4.9 MeV proton energy, with fine energy resolution. The excitation function averaged over about 100 keV energy interval exhibits “intermediate width structures”. Detailed statistical analysis of the data has revealed the presence of two kinds of structures having average widths which are characteristic of the compound nuclear and intermediate reaction mechanisms. The level spacings of these intermediate structures are consistent with Izumo's partial equilibrium model.     

Contents and Indexes of Volume 50 (2000)

Volume Contents

Contents and Indexes of Volume 50 (2000)     

Sergey Viktorovich Egerev (On his 50th birthday)

Chronicle

Sergey Viktorovich Egerev (On his 50th birthday)     

Contents volumes 26–50 (1984–1991)

Contents volumes 26–50 (1984–1991)     

Heredity of clusters in the rapidly cooling processes of Al-doped Zr_(50)Cu_(50) melts and its correlation with the glass-forming ability

The heredity of clusters in rapidly cooled(Zr_(50)Cu_(50))_(100-x)Al_x melts and its correlation with glass-forming ability(GFA) are studied via molecular dynamics simulations. Pair distribution function and the largest standard cluster(LSC)are adopted to characterize the local atomic structures in the(Zr_(50)Cu_(50))_(100-x)Al_x systems. The [12/555] icosahedra and their medium-range order(IMRO) play an important role in forming(Zr_(50)Cu_(50))_(100-x)Al_x metallic glasses(MGs). The fraction of [12/555], the number of IMRO, and the maximum size of IMRO in MGs increase significantly with increasing x. A tracking study further reveals that the configuration heredity of icosahedral clusters starts from supercooled liquids.No direct correlation exists between the GFA and the onset temperature of continuous or stated heredity. Instead, a larger hereditary supercooled degree of icosahedra matches with better GFA of Al-doped Zr_(50)Cu_(50) alloys.     

Influence of Zr_(50)Cu_(50) thin film metallic glass as buffer layer on the structural and optoelectrical properties of AZO films

Aluminum-doped ZnO(AZO) thin films with thin film metallic glass of Zr(50)Cu(50) as buffer are prepared on glass substrates by the pulsed laser deposition. The influence of buffer thickness and substrate temperature on structural, optical, and electrical properties of AZO thin film are investigated. Increasing the thickness of buffer layer and substrate temperature can both promote the transformation of AZO from amorphous to crystalline structure, while they show(100)and(002) unique preferential orientations, respectively. After inserting Zr(50)Cu(50) layer between the glass substrate and AZO film, the sheet resistance and visible transmittance decrease, but the infrared transmittance increases. With substrate temperature increasing from 25℃ to 520℃, the sheet resistance of AZO(100 nm)/Zr(50)Cu(50)(4 nm) film first increases and then decreases, and the infrared transmittance is improved. The AZO(100 nm)/Zr(50)Cu(50)(4 nm) film deposited at a substrate temperature of 360℃ exhibits a low sheet resistance of 26.7 ?/, high transmittance of 82.1% in the visible light region, 81.6% in near-infrared region, and low surface roughness of 0.85 nm, which are useful properties for their potential applications in tandem solar cell and infrared technology.     

Generation of 10(11) contrast 50 TW laser pulses

We demonstrate what we believe to be the highest-contrast (10(11)), multiterawatt, chirped-pulse amplification (CPA) Ti:sapphire laser by applying the modified cross-polarized-wave (XPW) generation method. This method produces a contrast improvement of 3 orders of magnitude using microjoule input energy. Microjoule energy can be achieved by direct amplification without the complications of a double CPA system. The 10(11) contrast is sufficient for experiments on high-damage-threshold solid targets with focused intensities up to 10(22) W/cm(2).     

锆钛比为50/50的PZT陶瓷极化前后的X射线研究

铁电陶瓷在极化及使用过程中有畴结构的变化。这种变化对材料宏观性能有直接影响.本文提出了一种从x 射线强度变化来定量地测定四方铁电相中90°畴转向率的简便方法. 只要正确地测定出未极化状态的强度I_200_与I_002_之比以及极化状态相应的比值, 就可以直接求得极化过程90°畴转向的百分比. 公式推导过程考虑了结构因素及可能存在的择优取向.用上述方法对锆钛比为50 / 50 的PZT 陶瓷在不同极化条件下90°畴的转向率作了计算, 所得的结果与宏观性能变化平行. 与过去用测量形变进行间接换算的方法作了比较. 文中还讨论了用x 射线线形变宽方法来测定极化前后的内应力问题. 关键词：