The Electromigration Force in Metallic Bulk

The voltage induced driving force on a migrating atom in a metallic system is discussed in the perspective of the Hellmann-Feynman force concept, local screening concepts and the linear-response approach. Since the force operator is well defined in quantum mechanics it appears to be only confusing to refer to the Hellmann-Feynman theorem in the context of electromigration. Local screening concepts are shown to be mainly of historical value. The physics involved is completely represented in ab initio local density treatments of dilute alloys and the implementation does not require additional precautions about screening, being typical for jellium treatments. The linear-response approach is shown to be a reliable guide in deciding about the two contributions to the driving force, the direct force and the wind force. Results are given for the wind valence for electromigration in a number of FCC and BCC metals, calculated using an {\it ab initio} KKR-Green's function description of a dilute alloy.Comment: 14 pages, 1 Postscript figur

‘Giant’ magnetoresistance in obliquely co-evaporated Co-Ag films

Magnetoresistance (MR) measurements at room temperature have been performed on obliquely (co-) evaporated Ag-Co films deposited at room- and elevated-temperatures. The ‘giant’ magnetoresistance ratio (max. 13% for a composition of about Co35Ag65) over a wide range of compositions has been measured. The films are polycrystalline and grown in a columnar morphology. The columnar diameter depends on the thickness and is < 20 nm at 400 nm thickness. From XRD, NMR and saturation magnetization (Ms) vs. at% Ag, one can conclude that the films consist of Co-Co and Ag-Ag clusters. The coercivity depends on the thickness of the films (100–700 nm) and varies from 5 to 15 kA/m

A re-evaluation of the Type D personality effect

Objective Type D personality has been associated with various medical and psychosocial outcomes. Type D's underlying personality traits negative affectivity (NA) and social inhibition (SI) are hypothesized to either additively (NA + SI) or synergistically (NA ∗ SI) affect an outcome. As some of the methods used to assess a Type D effect have been criticized in the past, this study aimed to investigate for all commonly used methods their tendency of producing false positive Type D effect. Method 324,000 datasets were generated using a Monte Carlo Simulation. Each dataset was analyzed using various methods to assess a Type D effect. Each method's performance was assessed in terms of absolute bias and the percentage of false positive findings. An online application was developed where readers can easily experiment with this simulation. Results Our simulation showed that all commonly used methods risk producing false positive Type D effects. The only method with adequate false positive rates included the continuous NA and SI main effects, as well as their quadratic effects and their interaction. Conclusion All commonly used methods to assess a Type D personality effect showed inflated false positive rates in realistic simulation scenarios. All earlier research based only on these methods should be reconsidered

Modeling synergy:How to assess a Type D personality effect

Objective In research on Type D personality, its subcomponents negative affectivity (NA) and social inhibition (SI) are hypothesized to have a synergistic effect on various medical and psychosocial outcomes. As some methods to analyze Type D personality have been criticized, this study investigated whether these methods adequately detect a Type D effect. Method We used a simulation and two empirical illustrations to investigate each method's performance (bias, power and false positives) in detecting the Type D effect. Results Our simulation showed that the two most commonly used methods to assess the Type D effect (subgroup methods) were primarily picking up the presence of NA or SI main effects, indicating that these methods might falsely suggest synergistic Type D effects. Moreover, these methods failed to detect the combined presence of the NA and SI main effects, resulting in significant Type D effects when only one of the NA/SI main effects was present. The method that best detected Type D effects modeled the continuous NA/SI main effects and their statistical interaction in a regression analysis. Reanalysis of two empirical Type D personality datasets confirmed the patterns found in our simulation. Conclusion This study showed that Type D effects should be modeled with a continuous interaction approach. Other approaches showed either more bias, more false positive findings or lower power. We recommend against using subgroup approaches to operationalize Type D personality, as these methods are biased, regardless of whether the Type D effect is synergistic or additive in nature

Neutron reflectometry on Co-Cr layers

Polarized neutron reflection experiments were performed on a thin in-plane magnetized Co-Cr layer deposited on a quartz substrate. Data taken at a low magnetic field ( 0.1 T) clearly indicate the existence of an initial layer at the substrate side, whereas data at saturation ( 0.7 T) are consistent with a rather homogeneous magnetization

Resistivity due to low-symmetrical defects in metals

The impurity resistivity, also known as the residual resistivity, is calculated ab initio using multiple-scattering theory. The mean-free path is calculated by solving the Boltzmann equation iteratively. The resistivity due to low-symmetrical defects, such as an impurity-vacancy pair, is calculated for the FCC host metals Al and Ag and the BCC transition metal V. Commonly, 1/f noise is attributed to the motion of such defects in a diffusion process.Comment: 24 pages in REVTEX-preprint format, 10 Postscript figures. Phys. Rev. B, vol. 57 (1998), accepted for publicatio

Giant magnetoresistance in Co/Cu multilayers sputtered with Kr

This paper presents some results of magnetoresistance measurements on Kr-sputter-deposited Co/Cu multilayers. We find that Co/Cu MLs sputtered with Kr gas show a larger GMR effect than those sputtered with Ar gas

Theory for the electromigration wind force in dilute alloys

A multiple scattering formulation for the electromigration wind force on atoms in dilute alloys is developed. The theory describes electromigration via a vacancy mechanism. The method is used to calculate the wind valence for electromigration in various host metals having a close-packed lattice structure, namely aluminum, the noble metals copper, silver and gold and the $4d$ transition metals. The self-electromigration results for aluminum and the noble metals compare well with experimental data. For the $4d$ metals small wind valences are found, which make these metals attractive candidates for the experimental study of the direct valence.Comment: 18 pages LaTeX, epsfig, 8 figures. to appear in Phys. Rev. B 56 of 15/11/199

Domain wall theory and exchange stiffness in Co/Pd multilayers

The stripe model of domain structure in multilayers is studied by micromagnetic simulation. The results indicate a strong reduction of the effective domain wall energy (by dipolar effects). Domain width measurements on sputtered Co/Pd multilayers are compared with the theory. The estimated exchange stiffness is comparable with that of bulk Co. The effects of interface roughness and of interlayer exchange are discussed