Pico-second spin dynamics in nano-structures: Towards nanometer spatial resolution by Transmission electron microscopy
Ferromagnetic resonance spectroscopy was employed to characterize the spectral properties of collective magnetic oscillations – spin-waves (magnons) – in individual chains of dipolar coupled magnetic nanoparticles. These biogenic particles have a diameter of about 35 nm, are arranged in magnetosomes (chains of particles) containing about 12 particles each, and are biologically synthesized in the bacterium Magnetospirillum Gryphiswaldense. The experiments show that the eigenmodes of individual nanoparticles, as well as complex coupling modes, can be spectroscopically resolved. The dipolar coupling between individual nanoparticles dominates the spectral properties of the eigenmodes. The presented results show that this coupling forms the basis for nano-sized spin-wave logic gates. Two genotypes, wild-type, and ∆-mamK mutant, are investigated. The geometric difference in the chain arrangements of the mutant and the wild type gives rise to distinct spectral properties. Based on the experimental results, two candidates for spin-wave logic gates are presented.The biological encoding of the chain geometry may, in the future, allow for genetically encoded magnonics circuits to be harvested from bacteria. A new measurement technique is developed, which enables the investigation of microwave dynamics, such as electron spin resonance, vortex dynamics, and ferromagnetic resonance, on the nanoscale using a transmission electron microscope. This technique allows, for the first time, to investigate the coupling between the electron beam, a microwave excitation, and a material’s response at frequencies of the order of 0.01 − 20 GHz. The dynamic deflection of the electron beam by such microwave fields yields spatially resolved insight into the resonant properties of micro- and nanostructures. Sensitivity to magnetic resonance is demonstrated using a standard paramagnetic marker material. Spatial resolution is observed in the ferromagnetic resonance modes of a magnetosome. An analytic model of the spectral response of confined magnets with chiral spin-spin coupling is derived. This model predicts resonant eigenmodes present only in chiral magnets. It gives the possibility to quantitatively derive the chiral coupling energy form ferromagnetic resonance spectra of confined chiral magnets.
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