Quantitative determination of vortex core dimensions in head-to-head domain walls using off-axis electron holography

Junginger, F.; Kläui, Mathias; Backes, Dirk; Krzyk, Stephen; Rüdiger, Ulrich; Kasama, Takeshi; Dunin-Borkowski, Rafal E.; Feinberg, Joshua M.; Harrison, R. J.; Heyderman, Laura J.

doi:10.1063/1.2829601

Cited by 21 publications

(11 citation statements)

References 19 publications

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“…techniques to tomographic imaging [8][9][10][11][12]. The introduction of three dimensionality provides additional degrees of freedom, and can result in novel properties [14,15] such as magnetochirality [15] and induced anisotropies [14], but the imaging is nevertheless limited to thin film investigations.…”

mentioning

confidence: 99%

Three-dimensional magnetization structures revealed with X-ray vector nanotomography

Donnelly

Guizar‐Sicairos

Scagnoli

et al. 2017

Nature

274

226

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In soft ferromagnetic materials, the smoothly varying magnetization leads to the formation of fundamental patterns such as domains, vortices and domain walls. These have been studied extensively in thin films of thicknesses up to around 200 nanometres, in which the magnetization is accessible with current transmission imaging methods that make use of electrons or soft X-rays. In thicker samples, however, in which the magnetization structure varies throughout the thickness and is intrinsically three dimensional, determining the complex magnetic structure directly still represents a challenge. We have developed hard-X-ray vector nanotomography with which to determine the three-dimensional magnetic configuration at the nanoscale within micrometre-sized samples. We imaged the structure of the magnetization within a soft magnetic pillar of diameter 5 micrometres with a spatial resolution of 100 nanometres and, within the bulk, observed a complex magnetic configuration that consists of vortices and antivortices that form cross-tie walls and vortex walls along intersecting planes. At the intersections of these structures, magnetic singularities-Bloch points-occur. These were predicted more than fifty years ago but have so far not been directly observed. Here we image the three-dimensional magnetic structure in the vicinity of the Bloch points, which until now has been accessible only through micromagnetic simulations, and identify two possible magnetization configurations: a circulating magnetization structure and a twisted state that appears to correspond to an 'anti-Bloch point'. Our imaging method enables the nanoscale study of topological magnetic structures in systems with sizes of the order of tens of micrometres. Knowledge of internal nanomagnetic textures is critical for understanding macroscopic magnetic properties and for designing bulk magnets for technological applications.

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confidence: 99%

Three-dimensional magnetization structures revealed with X-ray vector nanotomography

Donnelly

Guizar‐Sicairos

Scagnoli

et al. 2017

Nature

274

226

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“…In general the transverse wall is stable for narrower and thinner wires, whereas the vortex DW is the lowest energy configuration in wide, thick structures. In the transverse DW the magnetization forms a V-shaped arrangement with the magnetization rotating in the plane of the wire, whereas the vortex DW is similar to the vortex state in disks and squares with the magnetization rotating around a central core region which is out-of-plane magnetized, as revealed by electron holography [60].…”

Section: Magnetic Domain Wall Dynamicsmentioning

confidence: 99%

Imaging spin dynamics on the nanoscale using X-Ray microscopy

et al. 2015

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The dynamics of emergent magnetic quasiparticles, such as vortices, domain walls and bubbles are studied by scanning transmission X-ray microscopy (STXM), combining magnetic (XMCD) contrast with about 25 nm lateral resolution as well as 70 ps time resolution. Essential progress in the understanding of magnetic vortex dynamics is achieved by vortex core reversal observed by sub-GHz excitation of the vortex gyromode, either by ac magnetic fields or spin transfer torque. The basic switching scheme for this vortex core reversal is the generation of a vortex-antivortex pair. Much faster vortex core reversal is obtained by exciting azimuthal spin wave modes with (multi-GHz) rotating magnetic fields or orthogonal monopolar field pulses in the x and y direction, down to 45 ps in duration. In that way unidirectional vortex core reversal to the vortex core "down" or "up" state only can be achieved with switching times well below 100 ps. Coupled modes of interacting vortices mimic crystal properties. The individual vortex oscillators determine the properties of the ensemble, where the gyrotropic mode represents the fundamental excitation. By self-organized state formation we investigate distinct vortex core polarization configurations and understand these eigenmodes in an extended Thiele model. Analogies with photonic crystals are drawn. Oersted fields and spin-polarized currents are used to excite the dynamics of domain walls and magnetic bubble skyrmions. From the measured phase and amplitude of the displacement of domain walls we deduce the size of the non-adiabatic spin-transfer torque. For sensing applications, the displacement of domain walls is studied and a direct correlation between domain wall velocity and spin structure is found. Finally the synchronous displacement of multiple domain walls using perpendicular field pulses is demonstrated as a possible paradigm shift for magnetic memory and logic applications.

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“…[ 1–7 ] Therefore, several studies have been conducted on domain walls (DW) dynamics in nanostructures such as stripes. [ 8–14 ] This DW movement in magnetic devices has been achieved using a magnetic field [ 15–20 ] or spin‐transfer torque. [ 21–26 ] For functional DW memory, the DW should be pinned at a particular position in nanowires.…”

Section: Introductionmentioning

confidence: 99%

Chiral Dependence of Vortex Domain Wall Structure in a Stepped Magnetic Nanowire

Bahri

2021

Physica Status Solidi (a)

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Herein, vortex domain wall (VDW) with anticlockwise chirality (AVDW) and clockwise vortex domain wall (CVDW) with tail‐to‐tail magnetization configuration is studied using micromagnetic simulation. The VDW dynamics and the pinning potential are investigated in a new proposed device with a stepped area of length (l) and depth (d). Spin‐transfer torque is used to drive the domain wall (DW), which could act on the DW motion and stability required for facilitating the future design of the current‐induced DW motion devices. It is found that the VDW structural stability has a high dependence on the geometry of the stepped area (length l and depth d) and VDW chirality. The simulation results show that AVDW has higher structural stability than CVDW at the stepped area. In addition, the stepped nanowire geometries contribute to VDW trapping with a high potential barrier and high structural stability. Furthermore, the VDW speed increases with increasing d to reach 350 m s−1, and no apparent influence can be observed by changing l . All these findings could help in developing future storage memory with low power consumption, high speed, high DW stability, and large storage density.

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Quantitative determination of vortex core dimensions in head-to-head domain walls using off-axis electron holography

Cited by 21 publications

References 19 publications

Three-dimensional magnetization structures revealed with X-ray vector nanotomography

Three-dimensional magnetization structures revealed with X-ray vector nanotomography

Imaging spin dynamics on the nanoscale using X-Ray microscopy

Chiral Dependence of Vortex Domain Wall Structure in a Stepped Magnetic Nanowire

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