Ballistic electron transport through magnetic domain walls

Electron transport limited by the rotating exchange-potential of domain walls is calculated in the ballistic limit for the itinerant ferromagnets Fe, Co, and Ni. When realistic band structures are used, the domain wall magnetoresistance is enhanced by orders of magnitude compared to the results for previously studied two-band models. Increasing the pitch of a domain wall by confinement in a nano-structured point contact is predicted to give rise to a strongly enhanced magnetoresistance.Comment: 4 pages, 2 figures; to appear in PRB as a brief repor

An embedding potential definition of channel functions

We show that the imaginary part of the embedding potential, a generalised logarithmic derivative, defined over the interface between an electrical lead and some conductor, has orthogonal eigenfunctions which define conduction channels into and out of the lead. In the case of an infinitely extended interface we establish the relationship between these eigenfunctions and the Bloch states evaluated over the interface. Using the new channel functions, a well-known result for the total transmission through the conductor system is simply derived.Comment: 14 pages, 2 figure

Ab-initio-calculations of the GMR-effect in Fe/V multilayers

In a self-consistent semi-empirical numerical approach based on ab-initio-calculations for small samples, we evaluate the GMR effect for disordered (001)-(3--Fe/3--V)$_\infty$ multilayers by means of a Kubo formalism. We consider four different types of disorder arrangements: In case (i) and (ii), the disorder consists in the random interchange of some Fe and V atoms, respectively, at interface layers; in case (iii) in the formation of small groups of three substitutional Fe atoms in a V interface layer and a similar V group in a Fe layer at a different interface; and for case (iv) in the substitution of some V atoms in the innermost V layers by Fe. For cases (i) and (ii), depending on the distribution of the impurities, the GMR effect is enhanced or reduced by increasing disorder, in case (iii) the GMR effect is highest, whereas finally, in case (iv), a negative GMR is obtained (''inverse GMR'').Comment: LaTex, 30 pages, including 16 drawings; to appear in JMM

Spin Torques in Ferromagnetic/Normal Metal Structures

Recent theories of spin-current-induced magnetization reversal are formulated in terms of a spin-mixing conductance $G^{mix}$. We evaluate $G^{mix}$ from first-principles for a number of (dis)ordered interfaces between magnetic and non-magnetic materials. In multi-terminal devices, the magnetization direction of a one side of a tunnel junction or a ferromagnetic insulator can ideally be switched with negligible charge current dissipation.Comment: 4 pages, 1 figur

Universal distribution of transparencies in highly conductive Nb/AlOx_x/Nb junctions

We report the observation of the universal distribution of transparencies, predicted by Schep and Bauer [Phys. Rev. Lett. {\bf 78}, 3015 (1997)] for dirty sharp interfaces, in uniform Nb/AlO$_x$/Nb junctions with high specific conductance ($10^8$ Ohm$^{-1}$cm$^{-2}$). Experiments used the BCS density of states in superconducting niobium for transparency distribution probing. Experimental results for both the dc $I-V$ curves at magnetic-field-suppressed supercurrent and the Josephson critical current in zero magnetic field coincide remarkably well with calculations based on the multimode theory of multiple Andreev reflections and the Schep-Bauer distribution.Comment: 4 pages, 4 figures, references adde

Ideal Spin Filters: Theoretical Study of Electron Transmission Through Ordered and Disordered Interfaces Between Ferromagnetic Metals and Semiconductors

It is predicted that certain atomically ordered interfaces between some ferromagnetic metals (F) and semiconductors (S) should act as ideal spin filters that transmit electrons only from the majority spin bands or only from the minority spin bands of the F to the S at the Fermi energy, even for F with both majority and minority bands at the Fermi level. Criteria for determining which combinations of F, S and interface should be ideal spin filters are formulated. The criteria depend only on the bulk band structures of the S and F and on the translational symmetries of the S, F and interface. Several examples of systems that meet these criteria to a high degree of precision are identified. Disordered interfaces between F and S are also studied and it is found that intermixing between the S and F can result in interfaces with spin anti-filtering properties, the transmitted electrons being much less spin polarized than those in the ferromagnetic metal at the Fermi energy. A patent application based on this work has been commenced by Simon Fraser University.Comment: RevTeX, 12 pages, 5 figure

Scattering theory of interface resistance in magnetic multilayers

The scattering theory of transport has to be applied with care in a diffuse environment. Here we discuss how the scattering matrices of heterointerfaces can be used to compute interface resistances of dirty magnetic multilayers. First principles calculations of these interface resistances agree well with experiments in the CPP (current perpendicular to the interface plane) configuration.Comment: submitted to J. Phys. D (special issue at the occasion of Prof. T. Shinjo's 60th birthday

Spin-accumulation and Andreev-reflection in a mesoscopic ferromagnetic wire

The electron transport though ferromagnetic metal-superconducting hybrid devices is considered in the non-equilibrium Green's function formalism in the quasiclassical approximation. Attention if focused on the limit in which the exchange splitting in the ferromagnet is much larger than the superconducting energy gap. Transport properties are then governed by an interplay between spin-accumulation close to the interface and Andreev reflection at the interface. We find that the resistance can either be enhanced or lowered in comparison to the normal case and can have a non-monotonic temperature and voltage dependence. In the non-linear voltage regime electron heating effects may govern the transport properties, leading to qualitative different behaviour than in the absence of heating effects. Recent experimental results on the effect of the superconductor on the conductance of the ferromagnet can be understood by our results for the energy-dependent interface resistance together with effects of spin- accumulation without invoking long range pairing correlations in the ferromagnet.Comment: 15 pages, 12 figures included, submitted to PR

External validation of clinical decision rules for children with wrist trauma

Background: Clinical decision rules help to avoid potentially unnecessary radiographs of the wrist, reduce waiting times and save costs. Objective: The primary aim of this study was to provide an overview of all existing non-validated clinical decision rules for wrist trauma in children and to externally validate these rules in a different cohort of patients. Secondarily, we aimed to compare the performance of these rules with the validated Amsterdam Pediatric Wrist Rules. Materials and methods: We included all studies that proposed a clinical prediction or decision rule in children presenting at the emergency department with acute wrist trauma. We performed external validation within a cohort of 379 children. We also calculated the sensitivity, specificity, negative predictive value and positive predictive value of each decision rule. Results: We included three clinical decision rules. The sensitivity and specificity of all clinical decision rules after external validation were between 94% and 99%, and 11% and 26%, respectively. After external validation 7% to 17% less radiographs would be ordered and 1.4% to 5.7% of all fractures would be missed. Compared to the Amsterdam Pediatric Wrist Rules only one of the three other rules had a higher sensitivity; however both the specificity and the reduction in requested radiographs were lower in the other three rules. Conclusion: The sensitivity of the three non-validated clinical decision rules is high. However the specificity and the reduction in number of requested radiographs are low. In contrast, the validated Amsterdam Pediatric Wrist Rules has an acceptable sensitivity and the greatest reduction in radiographs, at 22%, without missing any clinically relevant fractures