Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films

We correlate simultaneously recorded magnetotransport and spatially resolved magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films micropatterned into Hall bars. Room temperature MOKE images reveal the nucleation and propagation of domains in an externally applied magnetic field and are used to extract a macrospin corresponding to the mean magnetization direction in the Hall bar. The anisotropic magnetoresistance calculated using this macrospin is in excellent agreement with magnetoresistance measurements. This suggests that the magnetotransport in Heusler compounds can be adequately simulated using simple macrospin models, while the magnetoresistance contribution due to domain walls is of negligible importance

Local charge and spin currents in magnetothermal landscapes

A scannable laser beam is used to generate local thermal gradients in metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study the resulting local charge and spin currents that arise due to the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as a function of the laser spot position and external magnetic field magnitude and orientation. The local SSE effect is detected in a similar fashion by exploiting the inverse spin Hall effect in a Pt layer deposited on top of the Y3Fe5O12. Our findings establish local thermal spin and charge current generation as well as spin caloritronic domain imaging

Einfluss der Kristallstruktur auf den Hall-Effekt in Co2YZ-Heusler-Verbindungen

Imort I-M. Einfluss der Kristallstruktur auf den Hall-Effekt in Co2YZ-Heusler-Verbindungen. Bielefeld: Universität Bielefeld; 2013

Direct measurement of the magnetic anisotropy of thin sputtered MgB2 films

Fabretti S, Imort I-M, Thomas A. Direct measurement of the magnetic anisotropy of thin sputtered MgB2 films. In: Verhandlungen der Deutschen Physikalischen Gesellschaft. Verhandlungen der Deutschen Physikalischen Gesellschaft. Vol 48. 2013.The simple hexagonal crystal structure and large London penetration depth make Magnesium-diboride an excellent candidate for spin polarization measurements using the Meservey-Tedrow method. In a step towards these measurements, we investigated the magnetic anisotropy of thin MgB2 films sputtered onto cubic (001)MgO and R-cut sapphire substrates. We present the high field cooling experiments with an applied magnetic field perpendicular and parallel to the film plane for those samples. These measurements were done in the high field laboratory in Nijmegen due to the required high upper critical field for thin sputtered films of up to 30 T. Our measurements show an upper critical field of 38.31 T with field parallel to the film plane and 27.7 T with a field perpendicular to the film plane for the samples with 120 nm MgB2. A linear fit shows a good approximation with the data points, although the parallel magnetic field could not destroy the superconductivity. We achieved a magnetic anisotropy ratio of 1.38. Literature values show an anisotropy ratio between 1.25 and 2 for thin films, which was fit with the Ginzburg Landau theory. Therefore our results agrees with the previously estimated anisotropy ratio for thin MgB2 films, where magnetic fields of up to 7 T were used

Transport measurements in superconductor/Heusler bilayers

Imort I-M, Fabretti S, Thomas P, Reiss G, Thomas A. Transport measurements in superconductor/Heusler bilayers. In: Verhandlungen der Deutschen Physikalischen Gesellschaft. Verhandlungen der Deutschen Physikalischen Gesellschaft. Vol 47. 2012.Superconductivity and ferromagnetism are two contrary phenomena due to their electronic properties. The investigation of superconductor (S)/ferromagnet (F) heterostructures has attracted a lot of scientific interest since they allow studying the interplay between superconductivity and ferromagnetism. Additionally, applications seem possible such as F/S/F spin valves and S/F/S π-junctions. Using transport- and magnetotransport-measurements, we investigate the behavior of the superconducting transition temperature T{sub c} in NbTi/Co{sub 2}FeSi bilayers as a function of different layer thicknesses and for varying magnetic moments of the Co{sub 2}FeSi layers. Using rf-magnetron sputtering, NbTi/Co{sub 2}FeSi bilayers were grown on single-crystalline MgO(001) substrates and in-situ annealed at different temperatures. The layered character of our samples has been tested by X-ray diffraction (XRD) scans. The electronic and magnetic transport measurements have been performed between 3 and 300 K with the magnetic field up to 4 T oriented in the film plane. The dependence of T{sub c} on the NbTi- and Co{sub 2}FeSi-layer thickness enables an estimation of the interface transparency of the NbTi/Co{sub 2}FeSi barrier in the framework of recent theoretical models

Fabrication of Superconducting MgB2 Thin Films by Magnetron co-Sputtering on (001) MgO Substrates

Fabretti S, Thomas P, Meinert M, Imort I-M, Thomas A. Fabrication of Superconducting MgB2 Thin Films by Magnetron co-Sputtering on (001) MgO Substrates. Journal Of Superconductivity And Novel Magnetism. 2013;26(5):1879-1882.We fabricated superconducting MgB2 thin films on (001) MgO substrates by magnetron rf and dc co-sputtering on heated substrates. We annealed the samples exsitu and in-situ at temperatures between 450 degrees C and 750 degrees C. The substrate temperature during the sputtering process and the post annealing temperatures play a crucial role in forming MgB2 superconducting thin films. We achieved a critical onset temperature of up to 27.1 K for the ex-situ and 25.6 K for the in-situ annealed samples at a film thickness of 30 nm. The samples shows an out of plane (0002)-Peak which was determined by x-ray diffraction