Inhomogeneous vortex-state-driven enhancement of superconductivity in nanoengineered ferromagnet-superconductor heterostructures

Thin film heterostructures provide a powerful means to study the antagonism between superconductivity (SC) and ferromagnetism (FM). One interesting issue in FM-SC hybrids which defies the notion of antagonistic orders is the observation of magnetic field induced superconductivity (FIS). Here we show that in systems where the FM domains/islands produce spatial inhomogeneities of the SC order parameter, the FIS can derive significant contribution from different mobilities of the magnetic flux identified by two distinct critical states in the inhomogeneous superconductor. Our experiments on nanoengineered bilayers of ferromagnetic CoPt and superconducting NbN where CoPt/NbN islands are separated by a granular NbN, lend support to this alternative explanation of FIS in certain class of FM-SC hybrids.Comment: 5 figure

Comment on "Mn Interstitial Diffusion in (Ga,Mn)As"

The magnetic and transport properties of (GaMn)As are known to be influenced by postgrowth annealing, and it is generally accepted that these modifications are due to outdiffusion of Mn interstitials. We show that the annealing-induced modifications are strongly accelerated if the treatment is carried out under As capping. This means that the modification rate is not limited by the diffusion process, but rather by the surface trapping of the diffusing species.Comment: 4 pages, 1 figur

Electron Spectroscopic Studies of Homogenous (GaMn) As Layers

By incorporating magnetism into semiconductors, it may possibly be viable to enhance the functionality of materials. An exceptionally important material in this context is GaAs, which can be doped with Mn atoms. (GaMn)As has fascinated research community as a promising candidate for spintronic application. It is quite appealing due to both its compatibility with existing III-V technology and great progress in improving its magnetic properties. Being fabricated by low temperature molecular beam epitaxy (LT-MBE), due to thermal instability at elevated temperatures, the material contains a high density of various defects compensating Mn acceptors. It is a well-established fact that the ferromagnetic state of (GaMn)As can be stabilized via post growth annealing. Nevertheless, in general, the annealed (GaMn)As layers do not remain useful for further epitaxial overgrowth that might be included in multilayer structure. We present a summary of our investigations regarding the synchrotron-based characterization of (GaMn)As layers grown via molecular beam epitaxy carried out at the Swedish National Facility of Synchrotron Radiation-the MAX-lab aiming at the reduction of the density of Mn interstitial and increase in the content of Mn

Organic molecular beam deposition system and initial studies of organic layer growth

This work describes an organic molecular beam deposition system with substrate entry/exit chamber, buffer chamber and with the possibility to transfer substrate from a III–V molecular beam deposition system. Flux calibrations of organic molecules and the initial growth of organic layers are described. For this purpose, the molecules 3,4,9,10 perylene tetra carboxylic dianhydride and copper phtalocyanine were used. Layers were grown on oxidized and hydrogen passivated Si(100), Indium tin oxide and glass respectively. The growth was investigated with atomic force microscopy, reflection high energy electron diffraction and ultraviolet photoemission spectroscopy. An investigation with x-ray photoelectron and Raman spectroscopy on the effect of atmospheric exposure is also included, showing little effect of surface pollution when the samples were handled carefully. The initial formation (monolayers) of copper phtalocyanine thin films was studied by ultraviolet photoemission spectroscopy

Organic molecular beam deposition system and initial studies of organic layer growth

This work describes an organic molecular beam deposition system with substrate entry/exitchamber, buffer chamber and with the possibility to transfer substrate from a III–V molecularbeam deposition system. Flux calibrations of organic molecules and the initial growth oforganic layers are described. For this purpose, the molecules 3,4,9,10 perylene tetra carboxylicdianhydride and copper phtalocyanine were used. Layers were grown on oxidized andhydrogen passivated Si(100), Indium tin oxide and glass respectively. The growth wasinvestigated with atomic force microscopy, reflection high energy electron diffraction andultraviolet photoemission spectroscopy. An investigation with x-ray photoelectron and Ramanspectroscopy on the effect of atmospheric exposure is also included, showing little effect ofsurface pollution when the samples were handled carefully. The initial formation (monolayers)of copper phtalocyanine thin films was studied by ultraviolet photoemission spectroscopy

Photoelectron spectroscopic studies of ultra-thin CuPc and PTCDA layers on Cu(100)

The initial interaction and interface formation between Cu(100) and the organic semiconductors 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) and copper phtalocyanine (CuPc) has been studied by means of angle-resolved UV photoelectron spectroscopy (ARUPS). Both CuPc and PTCDA are known to adsorb strongly on the Cu(100) surface. The bonding interaction is revealed via interface-related structures in photoemission spectra. However, the spectra develop rather differently in the low coverage regime: while CuPc molecular states are observed below monolayer coverage, the first PTCDA layer is found to be reacted such that the adsorbate-induced emission is strongly modified relative that of intact PTCDA molecules. We find a number of structures that are neither PTCDA- nor Cu-derived, and that the oxygen-related component of the PTCDA spectrum is completely missing in spectra from the monolayer. Importantly for device applications, we find evidence of interfacial electronic states in the form of new peaks located in the former HOMO-LUMO gap for both molecules. In the case of PTCDA these support a chemisorptive bonding model, whereas in the case of CuPc we interpret the state as a monolayer-specific resonance

GaSb/GaAs quantum dot systems

GaSb/GaAs quantum dot systems : in situ synchrotron radiation x-ray photoelectron spectroscopy study / R. Claessen ... - In: Nanotechnology. 16. 2005. S. 1326-133