Direct observation of grain-boundary dislocations in the FeCo alloy

A unified dislocation theory of grain boundaries proposed earlier for simple cubic crystals has been extended to include the case of ordered and disordered body-centred-cubic structures. Pure symmetric and asymmetric tilt and pure twist boundaries have been treated in detail and extended to an arbitrary grain boundary. It is shown that a unique set of coincidence site lattices exists for both the symmetric and asymmetric boundaries and that each of these sets, in turn, depends upon the rotation axis which characterizes the boundary. Furthermore, a unique set of grain-boundary dislocations is associated with each of these coincidence site lattices. The results are then applied to the transmission electron microscopy studies carried out in Part 2 of the present study.On leave from The Materials Research Group, Department of Metallurgy, Indian Institute of Science Bangalore — 560012, India.     

Fluctuation conductivity in the vicinity of the superconducting transition

The conductivity of the metal in the vicinity of the superconductivity transition point has been obtained. The nonlinear fluctuation effects change the temperature dependence of the conductivity in a wide range of temperatures, in which fluctuation corrections to thermodynamic quantities are still small. At comparatively strong pair breaking these effects decrease the fluctuation correction, which may exceed the conductivity of normal metal far from the transition temperature.     

(Nd1-xPrx)10.5(FeCoZr)83.5B6合金显微结构和磁性能研究

采用部分过快淬加后续晶化退火工艺,制备出了最佳磁性能的(Nd1-xPrx)10.5(FeCoZr)83.5 B6(x=O、0.2、0.4、0.6、0.8、1.0)系列粘结磁体,研究了稀土Pr元素对快淬合金DTA曲线转折温度点、合金显微组织结构和粘结磁体磁性能的影响.Pr元素使合金非晶态的晶化转变温度和转化能降低,合金的显微组织结构变得较粗大和较不均匀,从而使快淬粘结磁体剩磁降低.随Pr含量的增加,磁体的内禀矫顽力Hci单调上升,剩磁Br单调下降,在x=0.6～0.8处(BH)m达到最大值70.6kJ·m3.     

Selective Supramolecular Fullerene-Porphyrin Interactions and Switching in Surface-Confined C(60)-Ce(TPP)(2) Dyads

The control of organic molecules, supramolecular complexes and donor-acceptor systems at interfaces is a key issue in the development of novel hybrid architectures for regulation of charge-carrier transport pathways in nanoelectronics or organic photovoltaics. However, at present little is known regarding the intricate features of stacked molecular nanostructures stabilized by noncovalent interactions. Here we explore at the single molecule level the geometry and electronic properties of model donor-acceptor dyads stabilized by van der Waals interactions on a single crystal Ag(111) support. Our combined scanning tunneling microscopy/spectroscopy (STM/STS) and first-principles computational modeling study reveals site-selective positioning of C(60) molecules on Ce(TPP)(2) porphyrin double-decker arrays with the fullerene centered on the π-system of the top bowl-shaped tetrapyrrole macrocycle. Three specific orientations of the C(60) cage in the van der Waals complex are identified that can be reversibly switched by STM manipulation protocols. Each configuration presents a distinct conductivity, which accounts for a tristable molecular switch and the tunability of the intradyad coupling. In addition, STS data evidence electronic decoupling of the hovering C(60) units from the metal substrate, a prerequisite for photophysical applications.     

EPR study of the electronic states of β′-(BEDT-TTF)(TCNQ)

β′-(BEDT-TTF)(TCNQ) is a compound of BEDT-TTF (=ET) and TCNQ molecules aligned orthogonally with each other, forming two-dimensional sheets and one-dimensional columns of 1/4-filled π band, respectively. It is known that the metal-insulator transition occurs at 330 K at ambient pressure. We have measured the electronic spin susceptibility by means of the EPR-NMR method at 50 MHz, and the angular dependence of g-factor and line width of EPR both at Q (34 GHz) and W (94 GHz) band. We successfully confirmed that the antiferromagnetic transition occurs in ET sheets and TCNQ columns, independently.     

Electronic and magnetic properties of dilute transition clusters in noble (or transition) metals

Using a realistic band structure for the host (noble or transition metal), we present a detailed study of the electronic and magnetic properties of transitional impurity clusters without interactions between the clusters. For the calculation of the one-electron properties, the Hartree-Fock environment effects are self-consistently taken into account by Friedel's rule. The impurity potentials and densities of states are very sensitive to the impurity-impurity interactions inside the clusters. For the calculation of the magnetic properties, the electron-electron interactions are taken into account in the random phase approximation, which allows one to obtain simple expressions for the specific heat and the low-temperature-dependent resistivity. These properties are expressed in terms of three characteristic temperatures T _f(1), T _f(2) ⁺ , and T _f(2) ^– corresponding to three different modes of spin fluctuations for the considered model. We present numerical results from the study of the local magnetic susceptibility, which depends on local environments via several combined effects. Our conclusions on nearly magnetic copper-based alloys are in good agreement with the experimental data. In particular, our calculations confirm that a magnetic moment appears on a nickel atom when it is surrounded by approximately eight nearest-neighboring Ni atoms.This publication is a part of a thesis to be presented at the University Louis Pasteur.     

Switching process between bistable positions of multiquantum flux tubes in a thin-film type I superconductor

A superconducting memory device based on a bistable vortex position represents an interesting storage medium for future Josephson computers. In order to study the operational mode of such a single-flux quantum memory cell, we use as a model system multiquantum flux tubes in a thin-film type I superconductor (Pb). By employing high-resolution stroboscopic magnetooptical flux detection, we are able to globally visualize both spatial and temporal behavior of rapidly switching individual flux tubes. All experimental results agree reasonably well with theoretical model considerations of the energy balance during the elementary switching process.Supported by a grant from the Deutsche Forschungsgemeinschaft.     

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

Sintered samples of (Nd_14.9 Dy_1.9) (Fe₆₅ Co₈ Cu_1.0 Ga_1.0 Nb_0.7)B_7.5 were prepared and subjected to stepwise annealing in the temperature range 875 K–675 K. The XRD and metallographic (optical and electron microscopy) studies reveal a multi-phase microstructure with each phase showing different solubility of the alloying additions. This alloy has T _C of 705 K with an intrinsic coercivity of 1000 kA/m and energy product of 250 kJ/m³ at RT. Solubility of Co into the matrix phase and that of Ga and Cu into the Nd-rich grain boundary phase are considered to be the main contributing factors for the significant enhancement in T _C and H _ci respectively of the multi-component alloy when compared to those of ternary NdFeB, wherein H _ci = 720 kA/m and T _C = 585 K.     

The magnetic structure of ferromagnetic filaments of a CoNi(P) alloy in a porous silicon matrix

The magnetic and resonance properties of CoNi(P) alloys, synthesized by chemical deposition as films on single crystal silicon substrates and as filaments in linear pores of porous silicon substrates, were studied by magnetization and ferromagnetic resonance measurements. It is established that CoNi(P) alloys of the same composition but different morphologies occur in states characterized by different degrees of nonequilibrium, which is manifested by different modes of the magnetization approach to saturation.     

Complex magnetic behavior at the surface of B2 ordered FeCr alloy

Bouzar et al. (1997) have recently investigated the surface of B2 FeCr alloy. In all cases of crystal growth 0 0 1, 1 1 0 and 1 1 1 they found the local polarization at the surface to be antiferromagnetically coupled with the subsurface layer in contrast to parallel coupling between Fe and Cr in bulk FeCr. In order to assert these results, we have investigated the local polarization of Fe at the (0 0 1) surface of this alloy with a tight-binding linear muffin tin Orbitals (TB-LMTO) model. Using general gradient approximation with Langreth-Mehl-Hu functional for p(1 × 1) and c(2 × 2) configurations we found the local polarization at the Fe surface layer to be antiferromagnetically coupled with the subsurface Cr layer and high magnetic moments compared to the bulk values.     

Development of a flow field structure in the vicinity of a circular cylinder in the presence of a laminar-turbulent transition

The Reynolds equations and the two-parameter differentialq-Ω model of turbulence are used to investigate a flow past a circular cylinder with an isothermal surface (temperature factorT _w0 = 0.5) at the Mach numberM _∞ = 5 in the range of Reynolds numbers Re = 10⁴-10⁸. It is demonstrated that the turbulization of flow leads to a shift of the separation point downstream, a reduction and stabilization of the separation zone length, a decrease in the maximum velocity in the separation zone, and an increase in the heat flux at the rear stagnation point compared with its value at the forward stagnation point.     

电化学沉积法制备Co_(0.36)Cu_(0.64)合金纳米线及其磁性

利用电化学沉积的方法制备了具有fcc结构的Co0.36Cu0.64合金纳米线阵列,并对样品在400-700℃进行了退火处理.X-射线衍射及磁测量结果显示,随着退火温度的升高CoCu合金出现相分离,伴随着相分离矫顽力显著增大.综合分析得到矫顽力的增加是由于纳米线中Co和cu的相分离使得一些Co的单畴颗粒分散在Cu之间造成的.     

Microstructure and magnetic properties of Fe(x)Ni(1-x) alloy nanoplatelets

Plate-like nanoparticles (or nanoplatelets) of Fe(x)Ni(1-x) (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) alloy were successfully synthesized through a simple sonochemical method. The shapes of the alloy nanoplatelets with different Fe atom contents are almost same. Their average diameters are about 50 nm, and their average thicknesses are several nanometers. The obtained Fe(x)Ni(1-x) alloy nanoplatelets are single-phased and have a face-centered cubic (FCC) crystal structure. The lattice constants of the alloy nanoplatelets are larger than the corresponding bulk value and increase with increasing Fe content. The surface oxidation of the alloy nanoplatelets leads to the lattice expansion. The alloy nanoplatelet powders are all ferromagnetic, and their saturation magnetizations are slightly lower than the corresponding bulk value. The saturation magnetic field and the coercivity increase with increasing Fe content. Magnetic hysteresis loops along the directions deviating different angles from the nanoplatelets plane are obviously different, indicating that the easy-axis is in the in-plane direction and the magnetization reversal is incoherent mode. The micromagnetic simulation results for the array composed of thirty-six Fe0.6Ni0.4 alloy nanoplatelets fit well with the measured data.     

Lithium disorder in the vicinity of the superionic phase transition in monoclinic and rhombohedral Li3In2(PO4)3

Rhombohedral and monoclinic modifications of the Li₃In₂(PO₄)₃ compound have been studied by X-ray diffraction, infrared (i.r.) analysis, Raman light scattering, differential thermal analysis (DTA), differential scanning calorimetry (DSC) and impedance spectroscopy, in a wide temperature range of 290–600 K. Analysis of the data allows the suggestion that the superionic phase transition, observed in these materials in the temperature interval 370–385 K, belongs to Faraday type phase transformations. PO₄ tetrahedra, which are a partition of the (In₂P₃O₁₂) ₃₀₀ ^3– rigid skeleton, have been found deformed. This seems to be due to an ordered lithium ion-vacancy distribution in the low temperature, non-superionic, polymorphs. With increasing temperature these deformations disappear. This disappearance can be caused by a decrease of the correlation length of the lithium ion-vacancy order.     

Heat-capacity anomaly in a wide vicinity of the critical point of the triethylamine—water phase transition

The behavior of the isobaric heat capacity in the triethylamine—water binary system has been investigated experimentally by the adiabatic calorimetry method. The possible physical models of the observed effects are discussed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 196–200, September–October, 2005.     

Effect of a magnetic field on the specific heat jump of a superconducting alloy containing paramagnetic impurities with local states within the gap

The effect of a uniform magnetic field on the specific heat jump \({\Delta C}\) of a superconductor containing paramagnetic impurities has been investigated. The impurities are described by the Shiba-Rusinov model. Taking the normalized position of the bound state within the BCS gap ε₀=0.8 and 0.0 and the parameter α(=〈S _z ² 〉/S²)=1.0 and 1/3 as typical values, we find the detailed dependence of \({\Delta C}\) on the impurity concentration \(\bar c\) and the transition temperature T_c. In some cases \({\Delta C}\) diverges at certain values of \(\bar c\) or T_c, signaling a change of the normal-superconductor phase transition from second order to first order.     

On the existence of bistable stationary states of electron traps in surface oxide layers on metals

Thermostimulated electron emission from metals is described using a modified system of the Blokhintsev equations, which takes into account the diffusion of filled electron traps from the metal to the surface oxide layer (thus reducing the system to a genetic model that is well-known in biology). Stationary numerical solutions of the Fokker-Planck equation for a stochastic modified system of the Blokhintsev equations are obtained. Conditions for the transition of a system of electron traps to a bistable state induced by external multiplicative noise are determined.     

(Fe0.5 Co0.5)73.5 Cu1 Mo3 Si13.5 B9合金高温磁性的研究

研究了460～580℃等温退火(30min)后纳米晶(Fe0.5 Co0.5)73.5 Cu1Mo3Si13.5B9合金高温软磁性能.结果表明,在Fe73.5Cu1Mo3Si13.5B9纳米晶合金中用Co取代部分Fe仍可形成双相纳米晶结构,并且可显著提高合金的高温特性.与Fe73.5Cu1Mo3Si13.5B9纳米晶软磁合金相比,其室温μi略有下降,但表征高温磁稳定性的居里温度明显提高,同时磁导率在高温下衰减变缓,从而拓宽了纳米晶软磁材料的高温使用范围.文中初步探讨了用Co取代部分Fe后使高温特性得到改善的机理.