Marek Vaňatka - Academia.edu (original) (raw)
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Papers by Marek Vaňatka
Journal of Physics: Condensed Matter, 2015
We have carried out measurements of domain wall dynamics in a Pt/Co/GdO x (t) wedge sample with p... more We have carried out measurements of domain wall dynamics in a Pt/Co/GdO x (t) wedge sample with perpendicular magnetic anisotropy. When driven by an easy-axis field H z in the presence of an in-plane field H x , the domain wall expansion along ±x is anisotropic, as expected for samples presenting Dzyaloshinskii-Moriya interaction. In the creep regime, the sign and the value of the domain wall velocity asymmetry changes along the wedge. We show that in our samples the domain wall speed vs. H x curves in the creep regime cannot be explained simply in terms of the variation of the domain wall energy with H x , as suggested by previous works. For this reason the strength and the sign of the Dzyaloshinskii-Moriya interaction (DMI) cannot be extracted from these measurements. To obtain reliable information on the DMI strength using magnetic field-induced domain wall dynamics, measurements have been arXiv:1504.00933v1 [cond-mat.mtrl-sci] 3 Apr 2015
Physical Review B, 2015
Dynamic switching of the vortex circulation in magnetic nanodisks by fast-rising magnetic field p... more Dynamic switching of the vortex circulation in magnetic nanodisks by fast-rising magnetic field pulse requires annihilation of the vortex core at the disk boundary and reforming a new vortex with the opposite sense of circulation. Here we study the influence of pulse parameters on the dynamics and efficiency of the vortex core annihilation in permalloy (Ni 80 Fe 20 ) nanodisks. We use magnetic transmission soft x-ray microscopy to experimentally determine a pulse rise time-pulse amplitude phase diagram for vortex circulation switching and investigate the time-resolved evolution of magnetization in different regions of the phase diagram. The experimental phase diagram is compared with an analytical model based on Thiele's equation describing highamplitude vortex core motion in a parabolic potential. We find that the analytical model is in good agreement with experimental data for a wide range of disk geometries. From the analytical model and in accordance with our experimental finding we determine the geometrical condition for dynamic vortex core annihilation and pulse parameters needed for the most efficient and fastest circulation switching. The comparison of our experimental results with micromagnetic simulations shows that the micromagnetic simulations of "ideal" disks with diameters larger than ∼250 nm overestimate nonlinearities in susceptibility and eigenfrequency. This overestimation leads to the core polarity switching near the disk boundary, which then in disagreement with experimental findings prevents the core annihilation and circulation switching. We modify the micromagnetic simulations by introducing the "boundary region" of reduced magnetization to simulate the experimentally determined susceptibility and in these modified micromagnetic simulations we are able to reproduce the experimentally observed dynamic vortex core annihilation and circulation switching.
Journal of Physics: Condensed Matter, 2015
We have carried out measurements of domain wall dynamics in a Pt/Co/GdO x (t) wedge sample with p... more We have carried out measurements of domain wall dynamics in a Pt/Co/GdO x (t) wedge sample with perpendicular magnetic anisotropy. When driven by an easy-axis field H z in the presence of an in-plane field H x , the domain wall expansion along ±x is anisotropic, as expected for samples presenting Dzyaloshinskii-Moriya interaction. In the creep regime, the sign and the value of the domain wall velocity asymmetry changes along the wedge. We show that in our samples the domain wall speed vs. H x curves in the creep regime cannot be explained simply in terms of the variation of the domain wall energy with H x , as suggested by previous works. For this reason the strength and the sign of the Dzyaloshinskii-Moriya interaction (DMI) cannot be extracted from these measurements. To obtain reliable information on the DMI strength using magnetic field-induced domain wall dynamics, measurements have been arXiv:1504.00933v1 [cond-mat.mtrl-sci] 3 Apr 2015
Physical Review B, 2015
Dynamic switching of the vortex circulation in magnetic nanodisks by fast-rising magnetic field p... more Dynamic switching of the vortex circulation in magnetic nanodisks by fast-rising magnetic field pulse requires annihilation of the vortex core at the disk boundary and reforming a new vortex with the opposite sense of circulation. Here we study the influence of pulse parameters on the dynamics and efficiency of the vortex core annihilation in permalloy (Ni 80 Fe 20 ) nanodisks. We use magnetic transmission soft x-ray microscopy to experimentally determine a pulse rise time-pulse amplitude phase diagram for vortex circulation switching and investigate the time-resolved evolution of magnetization in different regions of the phase diagram. The experimental phase diagram is compared with an analytical model based on Thiele's equation describing highamplitude vortex core motion in a parabolic potential. We find that the analytical model is in good agreement with experimental data for a wide range of disk geometries. From the analytical model and in accordance with our experimental finding we determine the geometrical condition for dynamic vortex core annihilation and pulse parameters needed for the most efficient and fastest circulation switching. The comparison of our experimental results with micromagnetic simulations shows that the micromagnetic simulations of "ideal" disks with diameters larger than ∼250 nm overestimate nonlinearities in susceptibility and eigenfrequency. This overestimation leads to the core polarity switching near the disk boundary, which then in disagreement with experimental findings prevents the core annihilation and circulation switching. We modify the micromagnetic simulations by introducing the "boundary region" of reduced magnetization to simulate the experimentally determined susceptibility and in these modified micromagnetic simulations we are able to reproduce the experimentally observed dynamic vortex core annihilation and circulation switching.