A. Conca

The role of the non-magnetic material in spin pumping and magnetization dynamics in NiFe and CoFeB multilayer systems

We present a study of the effective magnetization Meff and the effective damping parameter αeff by means of ferromagnetic resonance spectroscopy on the ferromagnetic (FM) materials Ni81Fe19 (NiFe) and Co40Fe40B20 (CoFeB) in FM/Pt, FM/NM, and FM/NM/Pt systems with the non-magnetic (NM) materials Ru, Cr, Al, and MgO. Moreover, for NiFe layer systems, the influence of interface effects is studied by way of thickness dependent measurements of Meff and αeff. Additionally, spin pumping in NiFe/NM/Pt is investigated by means of inverse spin Hall effect (ISHE) measurements. We observe a large dependence of Meff and αeff of the NiFe films on the adjacent NM layer. While Cr and Al do not induce a large change in the magnetic properties, Ru, Pt, and MgO affect Meff and αeff in different degrees. In particular, NiFe/Ru and NiFe/Ru/Pt systems show a large perpendicular surface anisotropy and a significant enhancement of the damping. In contrast, the magnetic properties of CoFeB films do not have a large influence of t...

Low spin-wave damping in amorphous Co40Fe40B20 thin films

A characterization of the magnetic properties of amorphous Co40Fe40B20 thin films, developed for low damping applications in magnon spintronics, using vector network analyzer ferromagnetic resonance (VNA-FMR) and the magneto-optical Kerr effect is presented. Our films show a very weak uniaxial anisotropy and a low Gilbert damping parameter (α=0.0042). The saturation magnetization MS extracted from the FMR measurements is 1250 kA/m. The frequency dependence of the first perpendicular standing spin waves mode on the applied magnetic field is used to determine the exchange constant A for this alloy resulting in a value of 1.5×10−11 J/m. These values are discussed in comparison to literature values for different CoFeB compositions and other related alloys.

Measurements of the exchange stiffness of YIG films using broadband ferromagnetic resonance techniques

Measurements of the exchange stiffness D and the exchange constant A of Yttrium Iron Garnet (YIG) films are presented. YIG films with thicknesses from 0.9 to 2.6 µm were investigated with a microwave setup in a wide frequency range from 5 to 40 GHz. The measurements were performed with the external static magnetic field applied in-plane and out-of-plane. The method of Schreiber and Frait (1996 Phys. Rev. B 54 6473), based on the analysis of the perpendicular standing spin wave mode frequency dependence on the applied out-of-plane magnetic field, was used to obtain the exchange stiffness D. This method was modified to avoid the influence of internal magnetic fields during the determination of the exchange stiffness. Furthermore, the method was also adapted for in-plane measurements. The results obtained using all methods are compared and values of D between (5.18 ± 0.01) 10−17 T m2 and (5.40 ± 0.02) 10−17 T m2 were obtained for different thicknesses. From this, the exchange constant was calculated to be A = (3.7 ± 0.4) pJm−1.

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

Relative weight of the inverse spin-Hall and spin-rectification effects for metallic polycrystalline Py/Pt, epitaxial Fe/Pt, and insulating YIG/Pt bilayers: Angular dependent spin pumping measurements

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

Magneto-optical investigation of the shape anisotropy of individual micron-sized magnetic elements

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

Spin-pumping through a varying-thickness MgO interlayer in Fe/Pt system

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

Determination of the spin Hall angle in single-crystalline Pt films from spin pumping experiments

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.

Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co2FeAl/MgO interface upon annealing

We quantify the relative weight of inverse spin Hall and spin rectification effects occurring in RF-sputtered polycrystalline permalloy, molecular beam epitaxy-grown epitaxial iron and liquid phase epitaxy-grown yttrium-iron-garnet bilayer systems with different capping materials. To distinguish the spin rectification signal from the inverse spin Hall voltage the external magnetic field is rotated in-plane to take advantage of the different angular dependencies of the prevailing effects. We prove that in permalloy anisotropic magnetoresistance is the dominant source for spin rectification while in epitaxial iron the anomalous Hall effect has an also comparable strength. The rectification in yttrium-iron-garnet/platinum bilayers reveals an angular dependence imitating the one seen for anisotropic magnetoresistance caused by spin Hall magnetoresistance.