Journal of Physics D: Applied Physics

Torrejón, J; Badini-Confalonieri, G A; Vázquez, M

doi: 10.1088/0022-3727/43/14/145001pmid: N/A

The aim of this work is to report on the influence of the presence of a magnetically hard layer with large thickness on the ferromagnetic resonance (FMR) behaviour of soft/hard biphase microwires. Such microwires consist of a FeSiB soft nucleus, an intermediate glass layer and a CoNi hard outer shell, and are prepared by the combined quenching and drawing technique with electrochemical deposition. The unusual FMR response observed for this biphase system is characterized by the presence of a multipeak absorption spectrum that depends on the static field and on the thickness of the hard phase by means of magnetoelastic coupling. For a thick enough CoNi layer, the internal stresses induced in the nucleus during the electroplating process are very strong, giving rise to three electromagnetic absorptions: one at a low frequency related to the CoNi shell and two at higher frequencies corresponding to the FeSiB nucleus which are ascribed to two well-defined magnetization regions with different magnetic anisotropies.

Seehra, M S; Singh, V; Dutta, P; Neeleshwar, S; Chen, Y Y; Chen, C L; Chou, S W; Chen, C C

doi: 10.1088/0022-3727/43/14/145002pmid: N/A

For nominal 3 and 9nm FePt nanoparticles coated with oleylamine/oleic acid and having a face-centred-cubic (fcc) structure, temperature variations (5300K) of magnetization M, ac susceptibility and for the frequency range fm = 0.11000Hz and electron magnetic resonance (EMR) spectra at 9.28GHz are reported. X-ray diffraction of the samples shows fcc structure with a lattice constant a = 3.84 and TEM characterization yields log-normal distributions of the particle sizes with average D = 3.15(0.16)nm and D = 8.70(0.12)nm for the 3nm and 9nm samples, respectively. M versus T data for the zero-field-cooled and field-cooled modes yield a blocking temperature TB = 15K (85K) for the 3nm (9nm) samples whereas the hysteresis loops at 5K yield a coercivity Hc = 0Oe (1.4kOe). Analysis of the data of TB at different fm determined from the peaks in in ac susceptibility and the temperature variation of the EMR spectra are used to determine the following parameters of the VogelFulcher relaxation for the 3nm (9nm) samples respectively: the attempt frequency fo = 8 × 1010Hz (2 × 1012Hz); inter-particle interaction temperature To = 3K (33K) and anisotropy Ka = 1.96 × 106ergscm3 (4.3 × 105ergscm3). The use of the above parameters for the calculations of the optimum size for magnetic hyperthermia is analysed and discussed.

Yamato, Y; Matsukawa, M; Murano, Y; Kobayashi, S; Suryanarayanan, R

doi: 10.1088/0022-3727/43/14/145003pmid: N/A

We have investigated the current-induced nonlinear conduction in a charge-ordered phase of two-electron doped manganites Ca1xCexMnO3 (x = 0.1 and 0.167). The substitution of Ce4+ ion for Ca2+site of the parent matrix causes two-electron doping with the chemical formula . Seebeck coefficient data of Ca0.9Ce0.1MnO3 are, in both its temperature dependence and its magnitude, very similar to those of Ca0.8Sm0.2MnO3, leading to further evidence for two-electron doping. The VI characteristics measured using a long pulsed current show a negative differential resistance and its associated giant electroresistance effect. It is demonstrated that a temperature rise across the samples due to Joule heating is not responsible for a huge decrease in resistance observed here.

Fan, Qi Hua; Liao, Xianbo; Xiang, Xianbi; Chen, Changyong; Hou, Guofu; Cao, Xinmin; Deng, Xunming

doi: 10.1088/0022-3727/43/14/145101pmid: N/A

Amorphous silicon (a-Si) based thin film tandem junction solar cells are simulated based on a uniform field collection model. From the photovoltaic parameters of a single junction a-Si top cell and a few amorphous silicongermanium (a-SiGe) bottom cells, the optimized a-Si/a-SiGe tandem cell can be predicted. The simulation results are in good agreement with the experiment. The highest efficiency a-Si/a-SiGe tandem cells are obtained with a combination of a-SiGe characteristics and a relatively large mismatch in the short circuit current between the top and bottom cells. A key reason for this behaviour is that the tandem cell may exhibit a larger fill factor than either one of the component cells under a certain current mismatch.

Han, Xiangyun; Gao, Yihua; Dai, Jiangnan; Yu, Chenhui; Wu, Zhihao; Chen, Changqing; Fang, Guojia

doi: 10.1088/0022-3727/43/14/145102pmid: N/A

Nonpolar a-plane ZnO films were deposited for the first time on nearly lattice-matched a-plane GaN templates using an in situ SiNx interlayer by the pulsed laser deposition method. The symmetric and asymmetric reciprocal space mappings reveal the broadening effects of the reciprocal lattice points and the residual biaxial in-plane tensile strain of a-plane ZnO to be 0.335% and 0.055% along the [0001] c-axis and p-axis, respectively. The photoluminescence spectrum at 85K is dominated by neutral donor-bound excitons and free-electron-to-bound (e-A0) emissions; relatively intense LO-phonon replicas of (e-A0) have also been observed in a-plane ZnO. Temperature-dependent PL spectra have also been discussed to identify the origin of the emission peaks. Up to fourth A1(LO) phonon mode can be observed to be enhanced significantly from the resonant Raman spectrum.

Heidemann, F; Brüggemann, R; Bauer, G H

doi: 10.1088/0022-3727/43/14/145103pmid: N/A

Analogously with Cu(In,Ga)Se2, CuInS2 shows a high degree of spatial inhomogeneities in structural, optical and electronic properties on the length scale of grain sizes and above which is caused by the grainy structure and the inhomogeneous growth of absorber layers. To analyse these locally fluctuating magnitudes, spectrally resolved photoluminescence measurements with high lateral resolution (1m) have been performed in a confocal microscope setup. Based on these data sets and on Planck's generalized law determination of the spatial variation in the splitting of the quasi-Fermi levels and access to the local absorbance is possible. A detailed analysis of these properties, crucial for the solar light conversion efficiency of a final cell, is made for a CuInS2 absorber layer for data obtained from statistically representative scan areas. A cross-correlation between the splitting of the local quasi-Fermi levels and the local absorbance of an absorber leads to the conclusion that the splitting of quasi-Fermi levels is strongly governed by the excess-carrier recombination via deep defects.

Brand, S; Abram, R A; Kaliteevski, M A

doi: 10.1088/0022-3727/43/14/145104pmid: N/A

A simple phase-matching approach is employed as a design aid to engineer surface plasmon polariton states at the interface of an indium tin oxide layer on the top of a Bragg reflector. By altering the details of the reflector, and in particular the ordering of the layers and the thickness of the layer adjacent to the indium tin oxide, it is possible to readily adjust the energy of these states. Examples of structures engineered to give rise to distinctive features in the reflectivity spectra above the bulk screened plasma frequency for states of both possible polarizations are presented.

Benard, N; Moreau, E

doi: 10.1088/0022-3727/43/14/145201pmid: N/A

Natural instability mechanisms are inherent in most laminar and turbulent flow configurations. Usually, these instabilities result in the formation of flow structures occurring at diverse spatial and time scales. An effective control requires an actuator able to bring momentum transfer over a wide range of frequencies to act on these instabilities. Promising results are expected for such control strategy because, according to stability theory, a small amplitude perturbation can be large enough to produce significant effects even at high Reynolds number. Moreover, simultaneous production of small perturbations at several frequencies can enhance or cancel non-linear interactions; this opens alternative methods for flow control. The focus of this study is to demonstrate the ability of plasma actuators to introduce flow perturbations at single and dual frequencies by simply adjusting the waveform of the voltage applied to the plasma actuator. The flows produced by a dielectric barrier discharge supplied by burst, superposition and ring modulations are described in temporal and frequential domains. The results confirm the potential of non-thermal plasma actuators to produce highly unsteady flows at single, double or multiple frequencies.

Kimura, Motohiro; Nakamura, Yoshiharu

doi: 10.1088/0022-3727/43/14/145202pmid: N/A

Electron swarm parameters (the electron drift velocity, the longitudinal diffusion coefficient, the ionization and attachment coefficients and the effective ionization coefficient) in pure CF3I were measured in the range of E/N over 1401000Td. These swarm parameters were analysed using a Boltzmann equation analysis, and a set of electron collision cross sections for the CF3I molecule was derived so that it was consistent with the measured electron swarm parameters in CF3I. The present set of electron collision cross sections of CF3I derived was used to calculate the limiting E/N values in CF3IN2 mixtures to confirm that the results of the calculation agreed well with the recent experimental results.

Mihailova, D; van Dijk, J; Grozeva, M; Hagelaar, G J M; van der Mullen, J J A M

doi: 10.1088/0022-3727/43/14/145203pmid: N/A

The influence of the geometry of a longitudinal hollow cathode discharge (HCD) excited in a Cu cathode and HeAr mixture is studied experimentally and theoretically. Special attention is devoted to the optimization of the HC length to obtain a stable and uniform laser medium with a high excitation efficiency. The influence of the cathode length is demonstrated experimentally by the behaviour of the 780.8nm Cu ion line. The dependence of the laser power and gain as a function of the cathode length segments is measured. The Plasimo modelling platform is used to construct a model allowing more profound studies of the plasma processes and plasma behaviour under different conditions. Calculations at different cathode lengths are made and typical results such as spatial potential and plasma density distributions are presented and discussed. It is demonstrated that when the cathode length is increased the plasma density at the centre of the cathode decreases and the discharge tends to separate into two independent parts causing axial non-uniformity and reducing the discharge efficiency. The results also suggest that there exist a lower limit of the cathode length. Below this limit an inversion of the axial electric field occurs, which can be regarded as a transition between the conventional and high-voltage HCD under the conditions under study.