Controlling the properties of vortex domain walls via magnetic seeding fields

Hankemeier, S.; Kobs, A.; Frömter, Robert; Oepen, Hans Peter

doi:10.1103/physrevb.82.064414

Cited by 10 publications

(11 citation statements)

References 32 publications

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“…The domain-walls internal structural changes correlate with * fstein@physnet.uni-hamburg.de the macroscopic motion of the wall. In addition, the excitation of walls just below the pinning threshold is analyzed.Kinked permalloy nanowires are suitable for controlled injection of vortex domain walls by external magnetic fields [20]. By widening the wire in the direction away from the kink a confining potential for the wall is generated as the domainwall energy is proportional to the wire width [21].…”

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Direct observation of internal vortex domain-wall dynamics

et al. 2014

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The motion of domain walls is influenced by their internal structure and their structural changes during motion. The macroscopic motion is well understood but the internal dynamics during motion have not been experimentally studied in detail. We study vortex domain walls excited by nanosecond long magnetic field pulses in a pinning potential and above the pinning threshold. The dynamic response is imaged by transmission x-ray microscopy and the structural changes are analyzed. From the directly observed inertial behavior of the wall the domain-wall mass equivalent is estimated. During motion, oscillations of both the vortex core around the center of the domain wall and the domain-wall width are observed. The wall shows a fully elastic behavior by compression and overexpansion when being pushed by the field. Magnetic domain walls in flat nanowires possess unique properties [1]. Although having a rather complex magnetization structure they are, to a large extent, describable as quasiparticles [2]. A controlled motion of these walls can be achieved by magnetic fields [3] and electric currents [4,5]. The equations of motion are first-order differential equations [6] compared to second-order differentials for classical particles. But like classical particles an inertial behavior of domain walls is expected [7] and has been observed for domain walls in nanowires [8][9][10]. This inertial behavior is expressed by an effective mass of the domain wall [7,8,11] that only exist for walls in motion. Their controllable motion under the influence of spin polarized currents and magnetic fields have led to several ideas for applications like nonvolatile memory, logic devices, and sensors [12][13][14]. In general, two types of domainwall motion exist. For low driving forces the walls move as almost rigid particles, while above the Walker breakdown internal dynamics govern the macroscopic motion [2]. The velocity is proportional to the driving force up to the Walker breakdown [2] and the walls move slower for forces just above it. Measurements have shown a good agreement of this behavior between the theoretical description and the macroscopic motion [3,15,16]. However, most experiments so far had no direct access to the internal dynamics of the domain walls that can have strong impact on their behavior. Time-resolved x-ray microscopy has been used to study domain-wall oscillations in confined potentials [11,17] and the fast generation of vortex domain walls [10]. The driven motion of the walls has only been observed in strong fields above the Walker breakdown [10] as strong Oersted field pulses are required for the fast generation of domain walls [18,19]. For applications a detailed understanding of the dynamics in lower driving forces is crucial. We present time-resolved x-ray microscopy of internal dynamics of vortex domain walls under the influence of magnetic field pulses. Oscillations of the wall width as well as of the vortex core are observed. The domain-walls internal structural changes correlate with * fstein@physnet.uni...

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confidence: 99%

“…Kinked permalloy nanowires are suitable for controlled injection of vortex domain walls by external magnetic fields [20]. By widening the wire in the direction away from the kink a confining potential for the wall is generated as the domainwall energy is proportional to the wire width [21].…”

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confidence: 99%

Direct observation of internal vortex domain-wall dynamics

et al. 2014

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“…Figure 8D shows a 2 µm wide stripline across a V-shaped 20 nm thick nanowire. By horizontal saturation with an external magnetic field vortex DWs can be created at the kink [67]. The wire widens in both directions away from the kink creating a potential well for the wall.…”

Section: Fast Domain Wall Generationmentioning

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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“…Typical pinning sites are notches or antinotches in straight or curved wires [20,22,23]. Alternatively, zigzag wires are used [24], in which domain walls can be easily created via an in-plane seeding field that is applied perpendicular to the main wire direction [25]. In spite of the frequent use of bent wires [24,[26][27][28][29][30][31][32][33][34][35][36], the influence of the wire geometry on the magnetic fine structure of the domain wall has not been investigated yet.…”

Section: Introductionmentioning

confidence: 99%

Domain Walls in Bent Nanowires

et al. 2017

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The influence of geometric parameters on the magnetic fine structure of domain walls in bent nanowires is investigated. The domain pattern in the soft-magnetic Co 39 Fe 54 Si 7 alloy is studied via scanning electron microscopy with polarization analysis and modeled via micromagnetic simulations. It is demonstrated that the bending angle affects details of the microstructure as well as the preponderant domain-wall type. A phenomenological model is developed that provides the global energy minimum of individual types of domain walls as a function of the geometric parameters of the wire. The results can be directly transferred to permalloy wires, as permalloy and Co 39 Fe 54 Si 7 alloy have a comparable magnetostatic exchange length.

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Controlling the properties of vortex domain walls via magnetic seeding fields

Cited by 10 publications

References 32 publications

Direct observation of internal vortex domain-wall dynamics

Direct observation of internal vortex domain-wall dynamics

Imaging spin dynamics on the nanoscale using X-Ray microscopy

Domain Walls in Bent Nanowires

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