E. Th. Papaioannou

Magneto-optic enhancement and magnetic properties in Fe antidot films with hexagonal symmetry

The magneto-optic and magnetic properties of hexagonal arrays of holes in optically thin iron films are presented. We analyze their dependence on the hole radius and compare the results to a continuous iron film of the same thickness. We observe a large enhancement of the magneto-optic Kerr rotation with respect to that of the continuous film, at frequencies where surface-plasmon excitations are expected. The spectral position of the Kerr maxima can be tuned by the size and the distance between the holes. Additional simulations are in very good agreement with the experiment and thus confirm the effect of the surface plasmons on the Kerr rotation. The altering of the magnetic properties by the hole array is also visible in the hysteretic behavior of the sample where a significant hardening is observed.

Structural, magnetic, and spectroscopic magneto-optical properties aspects of Pt–Co multilayers with intentionally alloyed layers

Polycrystalline Pt–Co multilayers with intentionally alloyed layers were grown by e-beam evaporation on polyimide, Si, and glass substrates. X-ray diffraction spectra show that the multilayered structure of the samples degrades as compared to conventional Pt–Co multilayers. This degradation depends on the compositional variation of the intentionally alloyed layers. Magnetometry measurements reveal enhanced magnetization values for all samples, exceeding even by 90% the one of bulk Co, at a temperature of 10 K. This is attributed to both Pt-induced and enhanced Co magnetic moments, according to x-ray magnetic circular dichroism experiments. Spectroscopic magneto-optic measurements reveal large negative polar Kerr rotation maxima at photon energies between 4 and 4.4 eV due to the intense magneto-optic response of spin-polarized Pt.

Role of bulk-magnon transport in the temporal evolution of the longitudinal spin-Seebeck effect

M. Agrawal, 2, ∗ V. I. Vasyuchka, A. A. Serga, A. Kirihara, 3 P. Pirro, T. Langner, M. B. Jungfleisch, A. V. Chumak, E. Th. Papaioannou, and B. Hillebrands Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany Graduate School Materials Science in Mainz, Gottlieb-Daimer-Strasse 47, 67663 Kaiserslautern, Germany Smart Energy Research Laboratories, NEC Corporation, Tsukuba 305-8501, Japan (Dated: May 11, 2014)

Annealing influence on the Gilbert damping parameter and the exchange constant of CoFeB thin films

We present a study of the influence of the annealing temperature Ta on the magnetic properties of Co40Fe40B20 thin films. Using a vector network analyzer ferromagnetic resonance (VNA-FMR) setup and the magneto-optical Kerr effect, the dependence of the Gilbert damping parameter α, the exchange constant A, the saturation magnetization as well as the coercive field and the Kerr signal on Ta is reported. Additionally, the correlation with the crystalline properties of the films studied by X-ray diffractometry is discussed. We found that while the damping parameter α and the coercive field show sharp changes starting at a certain Ta value, the exchange constant A and the Kerr signal show a steady evolution. A differential modification of the film surface compared to the bulk is discussed as a possible reason. In any case, we found that the low damping values are preserved at the first onset of crystallization.

Lack of correlation between the spin-mixing conductance and the inverse spin Hall effect generated voltages in CoFeB/Pt and CoFeB/Ta bilayers

We investigate spin pumping phenomena in polycrystalline CoFeB/Pt and CoFeB/Ta bilayers and the correlation between the effective spin mixing conductance

Observation of a hole-size-dependent energy shift of the surface-plasmon resonance in Ni antidot thin films

g^{\uparrow\downarrow}_{\rm eff}

Growth modes of nanocrystalline Ni/Pt multilayers with deposition temperature

and the obtained voltages generated by the spin-to-charge current conversion via the inverse spin Hall effect in the Pt and Ta layers. For this purpose we measure the in-plane angular dependence of the generated voltages on the external static magnetic field and we apply a model to separate the spin pumping signal from the one generated by the spin rectification effect in the magnetic layer. Our results reveal a dominating role of anomalous Hall effect for the spin rectification effect with CoFeB and a lack of correlation between

Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers

g^{\uparrow\downarrow}_{\rm eff}

Positive surface and perpendicular magnetic anisotropy in natural nanomorphous Ni/NiO multilayers

and inverse spin Hall voltages pointing to a strong role of the magnetic proximity effect in Pt in understanding the observed increased damping. This is additionally reflected on the presence of a linear dependency of the Gilbert damping parameter on the Pt thickness.

Magnetism and magneto-optics of nanocrystalline Ni∕Pt multilayers grown by e-beam evaporation at room temperature

A combined experimental and theoretical study of the magneto-optic properties of a series of nickel antidot thin films is presented. The hole diameter varies from 869 down to 636 nm, while the lattice periodicity is fixed at 920 nm. This results in an overall increase of the polar Kerr rotation with decreasing hole diameter due to the increasing surface coverage with nickel. In addition, at photon energies of 2.7 and 3.3 eV, where surface-plasmon excitations are expected, we observe distinct features in the polar Kerr rotation not present in continuous nickel films. The spectral position of the peaks exhibits a red shift with decreasing hole size. This is explained within the context of an effective medium theory by a change in the effective dielectric function of the Ni thin films.