Jan-Peter Wüstenberg

Determination of spin injection and transport in a ferromagnet/organic semiconductor heterojunction by two-photon photoemission

A fundamental prerequisite for the implementation of organic semiconductors (OSCs) in spintronics devices is the still missing basic knowledge about spin injection and transport in OSCs. Here, we consider a model system consisting of a high-quality interface between the ferromagnet cobalt and the OSC copper phthalocyanine (CuPc). We focus on interfacial effects on spin injection and on the spin transport properties of CuPc. Using spin-resolved two-photon photoemission, we have measured directly and in situ the efficiency of spin injection at the cobalt-CuPc interface. We report a spin injection efficiency of 85-90% for injection into unoccupied molecular orbitals of CuPc. Moreover, we estimate an electron inelastic mean free path in CuPc in the range of 1 nm and a 10-30 times higher quasi-elastic spin-flip length. We demonstrate that quasi-elastic spin-flip processes with energy loss < or = 200 meV are the dominant microscopic mechanism limiting the spin diffusion length in CuPc.

Surface spin polarization of the nonstoichiometric Heusler alloy Co2MnSi

Using a combined approach of spin-resolved photoemission spectroscopy, band structure and photoemission calculations we investigate the influence of bulk defects and surface states on the spin polarization of nonstoichiometric Co2MnαSi thin films (with α = 0.69 and α = 1.19) with bulk L21 order. We find that for Mn-poor alloys the spin polarization at the Fermi energy (EF ) is negative due to the presence of CoMn antisite and minority surface state contributions. In Mn-rich alloys, the suppression of CoMn antisites leads to a positive spin polarization at EF , and the influence of minority surface states on the photoelectron spin polarization is reduced.

Towards a full Heusler alloy showing room temperature half-metallicity at the surface

In this paper we investigate the surface spin polarization in a 100?nm Co2Cr0.6Fe0.4Al film grown ex situ epitaxially on MgO(1 0 0) with a 10?nm Fe buffer layer by means of spin-resolved photoemission. We show that a careful in situ preparation of the sample surface leads to values for the room temperature spin polarization up to 45% at the Fermi level. To our knowledge, this is the highest value measured so far at the surface region of a full Heusler alloy at room temperature.

Structural, chemical and electronic properties of the Co2MnSi(001)=MgO interface

The performance of advanced magnetic tunnel junctions built of ferromagnetic (FM) electrodes and MgO as an insulating barrier depends decisively on the properties of the FM/insulator interface. Here we investigate interface formation between the Co-based Heusler compound

Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films

{\mathrm{Co}}_{2}\mathrm{MnSi}

Energy-Resolved Electron-Spin Dynamics at Surfaces of p-Doped GaAs

(CMS) and MgO by means of Auger electron spectroscopy, low-energy electron diffraction, and low-energy photoemission. The studies are performed for different annealing temperatures (

Effects of post-growth annealing on structural and compositional properties of the Co2Cr0.6Fe0.4Al surface and its relevance for the surface electron spin polarization

{T}_{A}

Characterization of the Surface Electronic Properties of Co2Cr1−xFexAl

) and MgO layer coverages (4, 6, 10, 20, and 50 ML). Thin MgO top layers (

Spin Injection and Spin Dynamics at CuPC/GaAs(100) Interface

{t}_{\mathrm{MgO}}\ensuremath{\le}10

Indirect Magnetic Coupling of Manganese Porphyrin to a Ferromagnetic Cobalt Substrate

ML) show distinct surface crystalline distortions, which can only be partly healed out by annealing and, furthermore, lead to distinct adsorption of carbon species after the MgO surface is exposed to air. For