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We have investigated the structural phase transition of FeCo and FeNi nanoparticles by molecular dynamics (MD) simulation using the generalized embedded atom potential (GEAM). It is found that the phase varies with the atomic compositions and annealing processes. By using the Honeycutt and Andersen index (HA index), bond order parameters (BOP) and pair correlation function (PCF), we found that a BCC to defective icosahedra phase transition occurs in the FeCo nanoparticle when Co composition is increased to about 60 at %. In the FeNi nanoparticle, three phases have been identified, namely, the BCC phase, the mixed BCC/FCC phase, and the multilayer defective icosahedral phase, which correspond to the Ni compositions of 0-20 at %, 20-70 at %, and 70-100 at %, respectively. Our simulations have well reproduced the phase transition points and most of the phases observed in recent experiments. [ABSTRACT FROM AUTHOR]

Using first-principles method within the framework of the density functional theory, we study the formation energies and the binding energies of multiple hydrogen-mercury vacancy complex impurities (nH-VHg, n = 1,2,3,4) in Hg0.75Cd0.25Te. We find that, when mercury vacancies exist in Hg0.75Cd0.25Te, the formation of the complex impurity between H and VHg (1H-VHg) is easy and its binding energy is up to 0.56 eV. In this case, the deep acceptor level of mercury vacancy is passivated. As the hydrogen concentration increases, we find that the complex impurity between VHg and two hydrogen atoms (2H-VHg) is more stable than 1H-VHg. This complex passivates both the two acceptor levels introduced by mercury vacancy and neutralizes the p-type dopant characteristics of VHg in Hg0.75Cd0.25Te. Moreover, we find that the complex impurities formed by one VHg and three or four H atoms (3H-VHg, 4H-VHg) are still stable in Hg0.75Cd0.25Te, changing the VHg doped p-type Hg0.75Cd0.25Te to n-type material. [ABSTRACT FROM AUTHOR]

Based on semiempirical generalized embedded atom method (GEAM), we carried out molecular dynamics and Monte Carlo simulations to study the structural properties of FeCo and FeNi nanoparticles. It is found that these two kinds of nanoparticles possess a new stable quasicore-shell structure, no matter whether they are in molten or condensed state and whether they are prepared by annealing or quenching. In FeCo (FeNi) nanoparticles of various sizes and atom compositions, the quasicore-shell structure is always preferred, with the shell formed only by Fe atoms and the core formed by randomly distributed Co(Ni) and Fe atoms. We have also investigated the formation mechanism of the quasicore-shell structure by energy difference analysis of the pure and doped icosahedra structure of FeCo and FeNi nanoparticles. [ABSTRACT FROM AUTHOR]

Using the density functional theory and nonequilibrium Green's function method, we report the effect of the gold-single wall carbon nanotubes (SWCNTs) composite contacts on the electronic structures and the transport properties of the device constructed by SWCNTs [SWCNT(10,0) or SWCNT(5,5)] and gold electrodes. The transmissions of the devices are greatly improved due to the strong couplings between carbon and gold atoms of the composite contacts. As for SWCNT(10,0), the gold atoms in the composite contacts behave as n-type dopant and depress the Schottky barrier between SWCNT(10,0) and the gold electrode. Moreover, the negative differential resistance characteristics occurs in the devices constructed by gold-SWCNT(10,0) composite contacts. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) magnetic property testing system has been completed and successfully used to measure 3D hysteresis loci of soft magnetic material. This paper presents the techniques to characterize soft magnetic materials under 3D magnetic excitations in detail. Using three couples of excitation coils controlled by a computer to generate the magnetic fields in three orthogonal axes, various types of flux density loci, such as circular or elliptical rotating vectors of flux density with any given orientations in 3D space, can be obtained. Based on 3D finite element analysis and a comparative study, a sandwich arrangement comprising a sample, guard pieces, and search coils with double-layer structure was proposed. Compared with the conventional surface search coils, this arrangement can significantly improve the accuracy of measurement. The comprehensive calibration process and the experimental results of the 3D hysteresis loci of soft magnetic composite materials are also presented. [ABSTRACT FROM AUTHOR]

Provides information on a study which reveals the core loss measurement of a soft magnetic composite material under two-dimensional excitations. Principle of measurement; Experimental results; Conclusion.