Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the low-frequency range using a pick-up coil wound around the sample. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance was observed. The asymmetry is attributed to the formation of a hard magnetic crystalline phase at the ribbon surface. The experimental results are interpreted in terms of the surface impedance tensor. It is assumed that the ribbon consists of an inner amorphous region and surface crystalline layers. The coupling between the crystalline and amorphous phases is described through an effective bias field. A qualitative agreement between the calculated dependences and experimental data is demonstrated. The results obtained may be useful for development of weak magnetic-field sensors.Comment: 19 pages, 6 figure

Optical properties of MgCNi3MgCNi_3 in the normal state

We present the optical reflectance and conductivity spectra for non-oxide antiperovskite superconductor $MgCNi_{3}$ at different temperatures. The reflectance drops gradually over a large energy scale up to 33,000 cm$^{-1}$, with the presence of several wiggles. The reflectance has slight temperature dependence at low frequency but becomes temperature independent at high frequency. The optical conductivity shows a Drude response at low frequencies and four broad absorption features in the frequency range from 600 $cm^{-1}$ to 33,000 $cm^{-1}$. We illustrate that those features can be well understood from the intra- and interband transitions between different components of Ni 3d bands which are hybridized with C 2p bands. There is a good agreement between our experimental data and the first-principle band structure calculations.Comment: 4 pages, to be published in Phys. Rev.

Void Formation Study of Flip Chip in Package Using No-Flow Underfill

©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.DOI: 10.1109/TEPM.2008.2002951The advanced flip chip in package (FCIP) process using no-flow underfill material for high I/O density and fine-pitch interconnect applications presents challenges for an assembly process that must achieve high electrical interconnect yield and high reliability performance. With respect to high reliability, the voids formed in the underfill between solder bumps or inside the solder bumps during the no-flow underfill assembly process of FCIP devices have been typically considered one of the critical concerns affecting assembly yield and reliability performance. In this paper, the plausible causes of underfill void formation in FCIP using no-flow underfill were investigated through systematic experimentation with different types of test vehicles. For instance, the effects of process conditions, material properties, and chemical reaction between the solder bumps and no-flow underfill materials on the void formation behaviors were investigated in advanced FCIP assemblies. In this investigation, the chemical reaction between solder and underfill during the solder wetting and underfill cure process has been found to be one of the most significant factors for void formation in high I/O and fine-pitch FCIP assembly using no-flow underfill materials

Semi-Inclusive B\to K(K^*) X Decays with Initial Bound State Effects

The effects of initial $b$ quark bound state for the semi-inclusive decays $B\to K(K^*) X$ are studied using light cone expansion and heavy quark effective theory methods. We find that the initial bound state effects on the branching ratios and CP asymmetries are small. In the light cone expansion approach, the CP-averaged branching ratios are increased by about 2% with respect to the free $b$-quark decay. For $\bar B^0 \to K^- (K^{*-}) X$, the CP-averaged branching ratios are sensitive to the phase $\gamma$ and the CP asymmetry can be as large as 7% (14%), whereas for $B^-\to \bar K^0 (\bar K^{*0})X$ the CP-averaged branching ratios are not sensitive to $\gamma$ and the CP asymmetries are small ($< 1$). The CP-averaged branching ratios are predicted to be in the ranges $(0.53 \sim 1.5)\times 10^{-4}$ [$(0.25 \sim 2.0)\times 10^{-4}$] for $\bar B^0 \to K^- (K^{*-})X$ and $(0.77 \sim 0.84)\times 10^{-4}$ [$(0.67 \sim 0.74)\times 10^{-4}$] for $B^-\to \bar K^0 (\bar K^{*0}) X$, depending on the value of the CP violating phase $\gamma$. In the heavy quark effective theory approach, we find that the branching ratios are decreased by about 10% and the CP asymmetries are not affected. These predictions can be tested in the near future.Comment: 29 pages, 12 ps figure

Structural and electronic properties of Al nanowires: an ab initio pseudopotential study

The stability and electronic structure of a single monatomic Al wire has been studied using the ab initio pseudopotential method. The Al wire undergoes two structural rearrangements under compression, i.e., zigzag configurations at angles of $140^o$ and $60^o$. The evolution of electronic structures of the Al chain as a function of structural phase transition has been investigated. The relationship between electronic structure and geometric stability is also discussed. The 2p bands in the Al nanowire are shown to play a critical role in its stability. The effects of density functionals (GGA and LDA) on cohesive energy and bond length of Al nanostructures (dimmer, chains, and monolayers) are also examined. The link between low dimensional 0D structure (dimmer) to high dimensional 3D bulk Al is estimated. An example of optimized tip-suspended finite atomic chain is presented to bridge the gap between hypothetical infinite chains and experimental finite chains.Comment: 11 pages, 5 figure

Comment on ''the controlled charge ordering and evidence of the metallic state in Pr0.65_{0.65}Ca0.35_{0.35}MnO3_{3} films''

In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12} L133) Lee \QTR{it}{et al.} have studied the transport properties of Pr$_{0.65}$Ca$_{0.35}$MnO$_{3}$ thin films. They claimed that they are able to controlled the charge-ordered (CO) state by the lattice strains. We propose herein another alternative since another indexation of the orientation of the film can be found leading to almost no distortion of the cell, as compared to the bulk compound.Comment: 2 page