H. S. Körner

Snell's Law for Spin Waves.

We report the experimental observation of Snells law for magnetostatic spin waves in thin ferromagnetic Permalloy films by imaging incident, refracted, and reflected waves. We use a thickness step as the interface between two media with different dispersion relations. Since the dispersion relation for magnetostatic waves in thin ferromagnetic films is anisotropic, deviations from the isotropic Snells law known in optics are observed for incidence angles larger than 25° with respect to the interface normal between the two magnetic media. Furthermore, we can show that the thickness step modifies the wavelength and the amplitude of the incident waves. Our findings open up a new way of spin wave steering for magnonic applications.

Epitaxial Growth of Room-Temperature Ferromagnetic MnAs Segments on GaAs Nanowires via Sequential Crystallization

We investigate the incorporation of manganese into self-catalyzed GaAs nanowires grown in molecular beam epitaxy. Our study reveals that Mn accumulates in the liquid Ga droplet and that no significant incorporation into the nanowire is observed. Using a sequential crystallization of the droplet, we then demonstrate a deterministic and epitaxial growth of MnAs segments at the nanowire tip. This technique may allow the seamless integration of multiple room-temperature ferromagnetic segments into GaAs nanowires with high-crystalline quality.

Time Resolved Measurements of the Switching Trajectory of Pt/Co Elements Induced by Spin-Orbit Torques

We report the experimental observation of spin-orbit torque induced switching of perpendicularly magnetized Pt/Co elements in a time resolved stroboscopic experiment based on high resolution Kerr microscopy. Magnetization dynamics is induced by injecting subnanosecond current pulses into the bilayer while simultaneously applying static in-plane magnetic bias fields. Highly reproducible homogeneous switching on time scales of several tens of nanoseconds is observed. Our findings can be corroborated using micromagnetic modeling only when including a fieldlike torque term as well as the Dzyaloshinskii-Moriya interaction mediated by finite temperature.

Magnetic damping in poly-crystalline Co25Fe75: Ferromagnetic resonance vs. spin wave propagation experiments

We report on the investigation of the magnetic damping of a 10 nm thin, poly-crystalline Co25Fe75 film grown by molecular beam epitaxy. Ferromagnetic resonance (FMR) measurements reveal a low intrinsic magnetic damping αintFMR=(1.5±0.1)×10−3. In contrast, in patterned micrometer wide stripes, spin wave (SW) propagation experiments performed by time resolved scanning magneto-optical Kerr microscopy yield attenuation lengths on the order of 5–8 μm. From this quantity, we deduce an effective magnetic SW damping αeffSW, exp =(3.9±0.3)×10−3. For the system studied, this significant difference between both damping parameters is attributed to the non-negligible extrinsic contributions (local inhomogeneities and two-magnon scattering) to the magnetic losses which manifest themselves as a distinct inhomogeneous FMR linewidth broadening. This explanation is supported by micromagnetic simulations. Our findings prove that poly-crystalline Co25Fe75 represents a promising binary 3d transition metal alloy to be employed in magnonic devices with much longer SW attenuation lengths compared to other metallic systems.We report on the investigation of the magnetic damping of a 10 nm thin, poly-crystalline Co25Fe75 film grown by molecular beam epitaxy. Ferromagnetic resonance (FMR) measurements reveal a low intrinsic magnetic damping αintFMR=(1.5±0.1)×10−3. In contrast, in patterned micrometer wide stripes, spin wave (SW) propagation experiments performed by time resolved scanning magneto-optical Kerr microscopy yield attenuation lengths on the order of 5–8 μm. From this quantity, we deduce an effective magnetic SW damping αeffSW, exp =(3.9±0.3)×10−3. For the system studied, this significant difference between both damping parameters is attributed to the non-negligible extrinsic contributions (local inhomogeneities and two-magnon scattering) to the magnetic losses which manifest themselves as a distinct inhomogeneous FMR linewidth broadening. This explanation is supported by micromagnetic simulations. Our findings prove that poly-crystalline Co25Fe75 represents a promising binary 3d transition metal alloy to be employ...

Spatial constraints on the source of uniaxial anisotropy in (Ga,Mn)As films

We use time-resolved Kerr microscopy to perform ferromagnetic resonance experiments on nanostructured elements to show that strain is not the origin of the strong uniaxial in-plane anisotropy observed in (Ga,Mn)As films. From local angular dependent ferromagnetic resonance measurements we are able to extract the anisotropy constants. We observe no change of the strong uniaxial anisotropy in disks as small as 200 nm.