20 research outputs found
Direct visualization of dynamic magnetic coupling in a Co/Py bilayer with picosecond and nanometer resolution
We present a combination of ferromagnetic resonance (FMR) with spatially and
time-resolved X-ray absorption spectroscopy in a scanning transmission X-ray
microscope (STXM-FMR). The transverse high frequency component of the
resonantly excited magnetization is measured with element-specifity in a
Permalloy (Py) disk - Cobalt (Co) stripe bilayer microstructure. STXM-FMR
mappings are snapshots of the local magnetization-precession with nm spatial
resolution and ps temporal resolution. We directly observe the transfer of
angular momentum from Py to Co and vice versa at their respective
element-specific resonances. A third resonance could be observed in our
experiments, which is identified as a coupled resonance of Py and Co.Comment: Version submitted to Physical Review Applied with updated author list
and supplemental information (Ancillary file
Unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling
We report strong unidirectional anisotropy in bulk polycrystalline B20 FeGe
measured by ferromagnetic resonance spectroscopy. Bulk and micron-sized samples
were produced and analytically characterized. FeGe is a B20 compound with
inherent Dzyaloshinskii-Moriya interaction. Lorenz microscopy confirms a
skyrmion lattice at in a magnetic field of 150 mT.
Ferromagnetic resonance was measured at ,
near the Curie temperature. Two resonance modes were observed, both exhibit a
unidirectional anisotropy of in
the primary, and in the secondary
mode, previously unknown in bulk ferromagnets. Additionally, about 25 standing
spin wave modes are observed inside a micron-sized FeGe wedge, measured at room
temperature ( K). These modes also exhibit unidirectional
anisotropy
Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5-10 GHz frequency range
We present a scanning transmission x-ray microscopy setup combined with a
novel microwave synchronization scheme in order to study high frequency
magnetization dynamics at synchrotron light sources. The sensitivity necessary
to detect small changes of the magnetization on short time scales and nanometer
spatial dimensions is achieved by combination of the developed excitation
mechanism with a single photon counting electronics that is locked to the
synchrotron operation frequency. The required mechanical stability is achieved
by a compact design of the microscope. Our instrument is capable of creating
direct images of dynamical phenomena in the 5-10 GHz range, with 35 nm
resolution. When used together with circularly polarized x-rays, the above
capabilities can be combined to study magnetic phenomena at microwave
frequencies, such as ferromagnetic resonance (FMR) and spin waves. We
demonstrate the capabilities of our technique by presenting phase resolved
images of a 6 GHz nanoscale spin wave generated by a spin torque oscillator, as
well as the uniform ferromagnetic precession with ~0.1 deg amplitude at 9 GHz
in a micrometer-sized cobalt strip.Comment: 9 pages, 7 figure
Anaerobic Microbial Degradation of Hydrocarbons: From Enzymatic Reactions to the Environment
Hydrocarbons are abundant in anoxic environments and pose biochemical challenges to their anaerobic degradation by microorganisms. Within the framework of the Priority Program 1319, investigations funded by the Deutsche Forschungsgemeinschaft on the anaerobic microbial degradation of hydrocarbons ranged from isolation and enrichment of hitherto unknown hydrocarbon-degrading anaerobic microorganisms, discovery of novel reactions, detailed studies of enzyme mechanisms and structures to process-oriented in situ studies. Selected highlights from this program are collected in this synopsis, with more detailed information provided by theme-focused reviews of the special topic issue on 'Anaerobic biodegradation of hydrocarbons' [this issue, pp. 1-244]. The interdisciplinary character of the program, involving microbiologists, biochemists, organic chemists and environmental scientists, is best exemplified by the studies on alkyl-/arylalkylsuccinate synthases. Here, research topics ranged from in-depth mechanistic studies of archetypical toluene-activating benzylsuccinate synthase, substrate-specific phylogenetic clustering of alkyl-/arylalkylsuccinate synthases (toluene plus xylenes, p-cymene, p-cresol, 2-methylnaphthalene, n-alkanes), stereochemical and co-metabolic insights into n-alkane-activating (methylalkyl) succinate synthases to the discovery of bacterial groups previously unknown to possess alkyl-/arylalkylsuccinate synthases by means of functional gene markers and in situ field studies enabled by state-of-the-art stable isotope probing and fractionation approaches. Other topics are Mo-cofactor-dependent dehydrogenases performing O-2-independent hydroxylation of hydrocarbons and alkyl side chains (ethylbenzene, p-cymene, cholesterol, n-hexadecane), degradation of p-alkylated benzoates and toluenes, glycyl radical-bearing 4-hydroxyphenylacetate decarboxylase, novel types of carboxylation reactions (for acetophenone, acetone, and potentially also benzene and naphthalene), W-cofactor-containing enzymes for reductive dearomatization of benzoyl-CoA (class II benzoyl-CoA reductase) in obligate anaerobes and addition of water to acetylene, fermentative formation of cyclohexanecarboxylate from benzoate, and methanogenic degradation of hydrocarbons
Magnetocrystalline anisotropy and Gilbert damping in iron-rich Fe1−xSix thin films
The magnetocrystalline anisotropy of Fe1−xSix (0≤x≤0.4) epitaxial thin films on MgO(001) was studied by ferromagnetic resonance. The experimental results are in good agreement with theoretical predictions of ab initio electronic structure calculations using the fully relativistic Korringa-Kohn-Rostoker Green's function method within spin-density-functional theory. The Gilbert damping α is found to be isotropic by theory and experiment with a minimum at the composition x=0.2
Magnetic anisotropy and relaxation of single Fe/FexOy core/shell- nanocubes: A ferromagnetic resonance investigation
In this work a full angle dependent Ferromagnetic Resonance (FMR) investigation on a system of 20 separated Fe/FexOy nanocubes without dipolar coupling is reported. The angular magnetic field dependence of FMR spectra of 20 single particles and 2 dimers were recorded using a microresonator setup with a sensitivity of 106 μB at X-band frequencies. We determine an effective magnetocrystalline anisotropy field of 2K4,eff/M = 50 mT ± 5 mT for selected particles, which is smaller than the one of bulk Fe due to the core shell morphology of the particles. The FMR resonances have a linewidth of 4 mT ± 1 mT, corresponding to a magnetic effective damping parameter α = 0.0045 ± 0.0005 matching the values of high quality iron thin films. Numerical calculations taking into account the different angular orientations of the 24 particles with respect to the external magnetic field yield a good agreement to the experiment
Biologically encoded magnonics
International audienceSpin wave logic circuits using quantum oscillations of spins (magnons) as carriers of information have been proposed for next generation computing with reduced energy demands and the benefit of easy parallelization. Current realizations of magnonic devices have micrometer sized patterns. Here we demonstrate the feasibility of biogenic nanoparticle chains as the first step to truly nanoscale magnonics at room temperature. Our measurements on magnetosome chains (ca 12 magnetite crystals with 35 nm particle size each), combined with micromagnetic simulations, show that the topology of the magnon bands, namely anisotropy, band deformation, and band gaps are determined by local arrangement and orientation of particles, which in turn depends on the genotype of the bacteria. Our biomagnonic approach offers the exciting prospect of genetically engineering magnonic quantum states in nanoconfined geometries. By connecting mutants of magnetotactic bacteria with different arrangements of magnetite crystals, novel architectures for magnonic computing may be (self-) assembled
Spatially resolved GHz magnetization dynamics of a magnetite nano-particle chain inside a magnetotactic bacterium
Understanding magnonic properties of nonperiodic magnetic nanostructures requires real-space imaging of ferromagnetic resonance modes with spatial resolution well below the optical diffraction limit and sampling rates in the 5–100 GHz range. Here, we demonstrate element-specific scanning transmission x-ray microscopy-detected ferromagnetic resonance (STXM-FMR) applied to a chain of dipolarly coupled Fe3O4 nano-particles (40–50 nm particle size) inside a single cell of a magnetotactic bacterium Magnetospirillum magnetotacticum. The ferromagnetic resonance mode of the nano-particle chain driven at 6.748 GHz and probed with 50 nm x-ray focus size was found to have a uniform phase response but non-uniform amplitude response along the chain segments due to the superposition of dipolar coupled modes of chain segments and individual particles, in agreement with micromagnetic simulations