At Filip

Spin-injection device based on EuS magnetic tunnel barriers

We propose a spin-valve device consisting of a nonmagnetic semiconductor quantum well, sandwiched between ferromagnetic semiconductor layers that act as barriers. The total conductance through such a trilayer depends on the relative magnetization of the two ferromagnetic-barrier layers which act as “spin filters.” With respect to practical realization, EuS/PbS heterostructures may be a suitable candidate. The magnetoresistance should exceed 100% for a wide range of the thicknesses of both the quantum well and the ferromagnetic barriers. From a fundamental physics point of view, the device may not only give insight into the spin lifetimes of the nonmagnetic layer, but the strong spin accumulation taking place in the quantum well may lead to novel optical and nuclear magnetic resonance properties.

Mn diffusion and the thermal stability of tunneling spin polarization

We examine the role of Mn diffusion in the thermal stability of tunneling spin polarization P by directly measuring P of Al∕AlOx∕Co∕FeMn and Al∕AlOx∕Co90Fe10∕FeMn junctions using superconducting tunneling spectroscopy (STS). We confirm Mn diffusion in our junctions using x-ray photoelectron spectroscopy after an ultrahigh vacuum 500°C anneal. Surprisingly, and in contrast to the current belief, no drop in P is observed using STS. Therefore, though Mn diffuses significantly, it cannot be solely responsible for the drop in tunneling magnetoresistance observed after postdeposition anneals above 300°C.

Magnetic and structural properties of EuS for magnetic tunnel junction barriers

In view of potential applications as a spin filter in spintronic devices, we systematically studied the growth by sputtering of ferromagnetic EuS barriers. The relationship between growth and magnetic and transport properties, also in combination with magnetic and nonmagnetic materials, was investigated. We demonstrate that growth at lower substrate temperatures (200u200a°C), followed by an anneal step at elevated temperatures (430u200a°C), leads to improved magnetic and transport properties of the barrier layer. We tentatively attribute the observed low-temperature magnetoresistance of high-resistive Al/PbS/EuS/PbS/Gd devices to spin filtering.In view of potential applications as a spin filter in spintronic devices, we systematically studied the growth by sputtering of ferromagnetic EuS barriers. The relationship between growth and magnetic and transport properties, also in combination with magnetic and nonmagnetic materials, was investigated. We demonstrate that growth at lower substrate temperatures (200u200a°C), followed by an anneal step at elevated temperatures (430u200a°C), leads to improved magnetic and transport properties of the barrier layer. We tentatively attribute the observed low-temperature magnetoresistance of high-resistive Al/PbS/EuS/PbS/Gd devices to spin filtering.

Modeling interlayer exchange coupling in EuS/PbS/EuS trilayers

All-semiconducting EuS/PbS/EuS trilayers that show antiferromagnetic coupling were studied by superconducting quantum interference device magnetometry. We analyzed our measurements with a modified Stoner–Wohlfarth model from which the interlayer exchange energy and anisotropy were extracted based on the switching field from antiparallel to parallel alignment of the EuS layers and the zero-field susceptibility, respectively. Magnetic moment versus temperature curves were simulated by taking into account Brillouin type temperature dependence of the saturation magnetization of EuS. Despite their simplicity, the simulated curves show good qualitative agreement with the measurements when strong temperature dependence of interlayer coupling is assumed.

Interface spin–flip scattering model for point contact Andreev reflection

Point contact Andreev reflection measurements show a correlation between measured spin polarization and the interface scattering parameter Z extracted from fits of the modified Blonder–Tinkham–Klapwijk model to the conductance–voltage curves of superconductor/ferromagnet point contacts. We present a simple spin–flip scattering model which identifies Z2 as the effective scattering parameter and explains the observed exponential decay of the spin polarization.

Enhanced electrical spin injection and detection in biased lateral ferromagnet–semiconductor structures

The realization of a fully electrical semiconductor-based device making use of the electron spin is of fundamental importance for physically studying spin-related phenomena. We have performed a detailed theoretical analysis of the feasibility of all electrical spin injection and detection in semiconductors by means of ferromagnetic electrodes and including spin-selective interface barriers to overcome the impedance mismatch. Based on the Poisson and diffusion equation, including electric field effects, the expected resistance difference for parallel and anti-parallel configurations of the ferromagnetic electrodes is analytically calculated and the influence of the sample and measurement geometry is extensively investigated. In this paper, we propose a new measurement geometry, for which we predict a clearly larger spin accumulation over a larger distance. Electric fields created in different sample regions via extra bias voltages will compensate spin loss in side branches. Even when the spin diffusion length is orders of magnitude smaller than the semiconductor length, the magnetoresistance in lateral devices closely approaches values for vertical devices.