Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems

We report a theoretical study of the quasiparticle lifetime and the quasiparticle mean free path caused by inelastic electron-electron scattering in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based on spin-polarized calculations, which are performed within the $GW$ approximation for equiatomic and Co- and Ni-rich compounds, as well as for their constituents. We mainly focus on the spin asymmetry of the quasiparticle properties, which leads to the spin-filtering effect experimentally observed in spin-dependent transport of hot electrons and holes in the systems under study. By comparing with available experimental data on the attenuation length, we estimate the contribution of the inelastic mean free path to the latter.Comment: 10 pages, 10 figure

Spin-polarized current amplification and spin injection in magnetic bipolar transistors

The magnetic bipolar transistor (MBT) is a bipolar junction transistor with an equilibrium and nonequilibrium spin (magnetization) in the emitter, base, or collector. The low-injection theory of spin-polarized transport through MBTs and of a more general case of an array of magnetic {\it p-n} junctions is developed and illustrated on several important cases. Two main physical phenomena are discussed: electrical spin injection and spin control of current amplification (magnetoamplification). It is shown that a source spin can be injected from the emitter to the collector. If the base of an MBT has an equilibrium magnetization, the spin can be injected from the base to the collector by intrinsic spin injection. The resulting spin accumulation in the collector is proportional to $\exp(qV_{be}/k_BT)$, where $q$ is the proton charge, $V_{be}$ is the bias in the emitter-base junction, and $k_B T$ is the thermal energy. To control the electrical current through MBTs both the equilibrium and the nonequilibrium spin can be employed. The equilibrium spin controls the magnitude of the equilibrium electron and hole densities, thereby controlling the currents. Increasing the equilibrium spin polarization of the base (emitter) increases (decreases) the current amplification. If there is a nonequilibrium spin in the emitter, and the base or the emitter has an equilibrium spin, a spin-valve effect can lead to a giant magnetoamplification effect, where the current amplifications for the parallel and antiparallel orientations of the the equilibrium and nonequilibrium spins differ significantly. The theory is elucidated using qualitative analyses and is illustrated on an MBT example with generic materials parameters.Comment: 14 PRB-style pages, 10 figure

Designing nanotubes

An amphiphile molecule designed to be a light-induced switch, was found to form self-assembled, stable, uniform nanotubes. In this report an attempt to change the dimensions of the nanotube wall is described. The approach is based on a systematic change in the molecular design of the molecule i.e. on changing the length of the alkyl chains. A hydrophobic precursor for a new nanotube amphiphile is synthesized, in attempt to control the morphology of the nanotubes. The synthesis of the precursor is described and also the future plans towards the complete synthesis of the nanotube amphiphile are presented. We also highlight the mechanisms of two interesting reactions used in the synthesis; the Snieckus anionic Friedel-crafts cyclisation reaction and the Barton-Kellogg reaction.

Community learning for local change: advancing social innovation through higher education

This document summarizes the main findings of the ERASMUS+ Strategic Partnership ‘Community Learning for Local Change (CLLC)’. The CLLC project has been running from September 2018 to August 2021. The project was a cooperation of four universities, three NGOs and various local community partners. Our consortium presents new approach to promote creativity, entrepreneurial thinking and skills for designing innovation in close cooperation with the communities in which our universities are embedded