Magnetic Domain Wall Velocity Research Articles

Real-time probing technique of domain wall dynamic in perpendicularly magnetized film

We present the study of a rarely mentioned method for measuring the magnetic domain wall velocity, which makes it possible to have a real-time probing of the domain wall movement in the perpendicularly magnetized thin film. We have compared this technique in detail with the most common Kerr imaging method. The comparison results show interesting differences if the spot size is too small. It can be explained by the dendritic shape of the domain wall. By changing the size spot, we propose a basic model that describes quite well the transit time in the laser spot as a function of its size and makes it possible to extract the velocity and depth of the dendrites. By generalizing our method, it helps people to understand magnetic domain wall dynamics from the temporal dimension and helps the academic community to obtain intrinsic domain wall motion characteristics in the film sample, ultimately promoting the development of spintronic devices.

Elevation of Domain Wall Velocity Driven by Current Pulses in 2D Ferromagnetic Material Fe3GeTe2

AbstractControlling the domain wall motion in the 2D ferromagnetic materials is significantly critical to the topological spin electronics, non‐volatile magnetic memories, and logic devices. The elevation of the domain wall velocity has become an urgent challenge. Herein, a current‐pulse‐driving strategy is unprecedentedly established to boost the domain wall velocity with an out‐of‐plane magnetic field and a rising temperature in the Fe3GeTe2 by using the in situ Lorentz Transmission Electron Microscopy. Elevation of domain wall velocity depends on the demagnetization energy increase and Zeeman energy reduction, which originates from the magnetic moments tilting by a non‐parallel to the magnetic field. By injecting ≈2000 times of alternative current pulses, a uniform instead of an unsynchronized domain wall velocity is achieved. The key mechanism lies in the decrease of the domain wall number, leading to a reduction in the expansion and compression of the domain areas. Optimized pulse parameters are applied with a critical duration of 60 ns and the density of ≈2 × 1010 A m−2, leading to an elevation of velocity from 0.0308 to 0.39 m s−1. The elevation in magnetic domain wall velocity can be useful for the application of 2D van der Waals ferromagnetic materials in future spintronic devices.

Controlling magnetic domain wall velocity by femtosecond laser pulses

Using the technique of double high-speed photography, we find that a femtosecond laser pulse is able to change the velocity of a moving domain wall in an yttrium iron garnet. The change depends on the light intensity and the domain wall velocity itself. To explain the results we propose a model in which the domain wall velocity is controlled by photo-induced generation of vertical Bloch lines.

Domain wall energy and strain in Pt/Co/Ir thin films on piezoelectric transducers

We study the energy and creep velocity of magnetic domain walls in perpendicularly magnetised Pt/Co/Ir thin films under strain. We find that the enhancement of domain wall creep velocity under strain from piezoelectric transducers is largest in films with the thinnest Co layers (0.56 nm), in which the strain causes the smallest relative change in perpendicular magnetic anisotropy and the largest relative change in domain wall creep velocity. We show how domain wall energy is predictive of the sensitivity of domain wall creep velocity to changes in strain, and thus provide a route to designing magnetic thin film systems for optimum strain control.

19pPSB-48 フェリ磁性体GdFeCo細線における磁場駆動磁壁移動速度の温度依存性

19pPSB-48 フェリ磁性体GdFeCo細線における磁場駆動磁壁移動速度の温度依存性

Inversion of the domain wall propagation in synthetic ferrimagnets

We report on magnetic domain wall velocity measurements in a synthetic ferrimagnet made of two perpendicular ferromagnetic layers antiferromagnetically exchange coupled. In this system, two types of transitions may be observed: one from a parallel alignment to an antiparallel alignment of the magnetization of the two layers and the other between the two possible antiparallel alignments. Those transitions are shown to be dominated by domain wall propagation. The domain wall velocity as a function of the applied magnetic field pulse amplitude has been measured. Two remarkable features are observed: first, a drastic breakdown of the domain wall velocity and then an inversion of the domain propagation direction are observed when the field pulses reach values comparable to the exchange field between the two layers. This unexpected behavior can be understood qualitatively using a simple model taking into account the competition between interlayer exchange coupling and the external driving field.

Electric-field-driven domain wall dynamics in perpendicularly magnetized multilayers

We report on reversible electric-field-driven magnetic domain wall motion in a Cu/Ni multilayer on a ferroelectric BaTiO3 substrate. In our heterostructure, strain-coupling to ferroelastic domains with in-plane and perpendicular polarization in the BaTiO3 substrate causes the formation of domains with perpendicular and in-plane magnetic anisotropy, respectively, in the Cu/Ni multilayer. Walls that separate magnetic domains are elastically pinned onto ferroelectric domain walls. Using magneto-optical Kerr effect microscopy, we demonstrate that out-of-plane electric field pulses across the BaTiO3 substrate move the magnetic and ferroelectric domain walls in unison. Our experiments indicate an exponential increase of domain wall velocity with electric field strength and opposite domain wall motion for positive and negative field pulses. The application of a magnetic field does not affect the velocity of magnetic domain walls, but independently tailors their internal spin structure, causing a change in domain wall dynamics at high velocities.

Fast Magnetic Domain-Wall Motion in a Ring-Shaped Nanowire Driven by a Voltage.

Magnetic domain-wall motion driven by a voltage dissipates much less heat than by a current, but none of the existing reports have achieved speeds exceeding 100 m/s. Here phase-field and finite-element simulations were combined to study the dynamics of strain-mediated voltage-driven magnetic domain-wall motion in curved nanowires. Using a ring-shaped, rough-edged magnetic nanowire on top of a piezoelectric disk, we demonstrate a fast voltage-driven magnetic domain-wall motion with average velocity up to 550 m/s, which is comparable to current-driven wall velocity. An analytical theory is derived to describe the strain dependence of average magnetic domain-wall velocity. Moreover, one 180° domain-wall cycle around the ring dissipates an ultrasmall amount of heat, as small as 0.2 fJ, approximately 3 orders of magnitude smaller than those in current-driven cases. These findings suggest a new route toward developing high-speed, low-power-dissipation domain-wall spintronics.

Non-volatile polarization switch of magnetic domain wall velocity

Controlled propagation speed of individual magnetic domains in metal channels at the room temperature is obtained via the non-volatile field effect associated with the switchable polarization of P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) ferroelectric polymer. Polarization domains directly written using conducting atomic force microscope probe locally accelerate/decelerate the magnetic domains in the 0.6 nm thick Co film. The change of the magnetic domain wall velocity is consistent with the magnetic anisotropy energy modulation through the polarization upward/downward orientation. Excellent retention is observed. The demonstrated local non-destructive and reversible change of magnetic properties via rewritable patterning of ferroelectric domains could be attractive for exploring the ultimate limit of miniaturization in devices based on ferromagnetic/ferroelectric bilayers.

Excitation of magnetic domain wall velocity in (Co/Ni) nanowires induced by blocking the motion of vertical Bloch lines

We study the high-field-driven motion of a magnetic domain wall (DW) in a (Co/Ni) nanowire under the Dzyaloshinskii–Moriya interaction (DMI) by using micromagnetic simulations. The results show that the DW velocity above the Walker field (Hw) changes in response to not only the DMI strength but also the width of the nanowire. The DW velocity shows a re-increment depending on the magnetic field and reaches several hundred m/s, despite high-field regions above Hw. In the re-increment, the DW moves while maintaining its structure because the motion of vertical Bloch lines is blocked by the bending region of the DW.

Magnetic domain-wall velocity enhancement induced by a transverse magnetic field

Spin dynamics of field-driven domain walls (DWs) guided by permalloy nanowires are studied by high-speed magneto-optic polarimetry and numerical simulations. DW velocities and spin configurations are determined as functions of longitudinal drive field, transverse bias field, and nanowire width. Nanowires having cross-sectional dimensions large enough to support vortex wall structures exhibit regions of drive-field strength (at zero bias field) that have enhanced DW velocity resulting from coupled vortex structures that suppress oscillatory motion. Factor of 10 enhancements of the DW velocity are observed above the critical longitudinal drive-field (that marks the onset of oscillatory DW motion) when a transverse bias field is applied. Nanowires having smaller cross-sectional dimensions that support transverse wall structures also exhibit a region of higher mobility above the critical field, and similar transverse-field induced velocity enhancement but with a smaller enhancement factor. The bias-field enhancement of DW velocity is explained by numerical simulations of the spin distribution and dynamics within the propagating DW that reveal dynamic stabilization of coupled vortex structures and suppression of oscillatory motion in the nanowire conduit resulting in uniform DW motion at high speed. The enhanced velocity and drive field range are achieved at the expense of a less compact DW spin distribution.

Miniature coils for producing pulsed inplane magnetic fields for nanospintronics.

Nanospintronic and related research often requires the application of quickly rising magnetic field pulses in the plane of the studied planar structure. We have designed and fabricated sub-millimeter-sized coils capable of delivering pulses of the magnetic field up to ∼500 Oe in the plane of the sample with the rise time of the order of 10 ns. The placement of the sample above the coil allows for easy access to its surface with manipulators or light beams for, e.g., Kerr microscopy. We use the fabricated coil to drive magnetic domain walls in 1 μm wide permalloy wires and measure magnetic domain wall velocity as a function of the applied magnetic field.

Faceting oscillations in nano-ferroelectrics

We observe periodic faceting of 8-nm diameter ferroelectric disks on a 10 s time-scale when thin Pb(Zr0.52Ti0.48)O3 film is exposed to constant high-resolution transmission electron microscopy beams. The oscillation is between circular disk geometry and sharply faceted hexagons. The behavior is analogous to that of spin structure and magnetic domain wall velocity oscillations in permalloy [Bisig et al., Nat. Commun. 4, 2328 (2013)], involving overshoot and de-pinning from defects [Amann et al., J. Rheol. 57, 149–175 (2013)].

Electric-field control of magnetic domain-wall velocity in ultrathin cobalt with perpendicular magnetization

Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2-3 MV cm(-1) can change the magnetic domain wall velocity in its creep regime (10(6)-10(3) m s(-1)) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion.

Magnetic field insensitivity of magnetic domain wall velocity induced by electrical current in Co/Ni nanowire

We have investigated the velocity of magnetic domain wall (DW) motion induced by electric currents in a Co/Ni nanowire with a perpendicular magnetic anisotropy. The DW velocity increased as current density increased and the maximum velocity of 60 m/s was observed. Furthermore, the DW velocity was found to be almost independent of external perpendicular magnetic fields in the range of −50 to +50 Oe. The mechanism of the observed field insensitivity of the current induced DW motion is also discussed.

Creep and Flow Regimes of Magnetic Domain-Wall Motion in UltrathinPt/Co/PtFilms with Perpendicular Anisotropy

We report on magnetic domain-wall velocity measurements in ultrathin Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, alpha.

Quantification of the Barkhausen noise method for the evaluation of time-dependent degradation

The Barkhausen noise (BN) method has long been applied to measure the bulk magnetic properties of magnetic materials. Recently, this important nondestructive testing (NDT) method has been applied to evaluate microstructure, stress distribution analysis, fatigue, creep and fracture characteristics. Until now the BN method has been used only qualitatively in evaluating the variation of BN with variations in material properties. For this reason, few NDT methods have been applied in industrial plants and laboratories. The present investigation studied the coercive force and BN while varying the microstructure of ultrafine-grained steels and SA508 cl.3 steels. This variation was carried out according to the second heat-treatment condition with rolling of ultrafine-grained steels and the simulated time-dependent degradation of SA 508 cl.3 steels. An attempt was also made to quantify BN from the relationship between the velocity of magnetic domain walls and the retarding force, using the coercive force of the domain wall movement. The microstructure variation was analyzed according to time-dependent degradation. Fracture toughness was evaluated quantitatively by measuring the BN from two intermediary parameters; grain size and distribution of nonmagnetic particles. From these measurements, the variation of microstructure and fracture toughness can be directly evaluated by the BN method as an accurate in situ NDT method.

Domain wall velocity and interrupted pulse experiments

The velocity of magnetic domain walls in Bloch wall Permalloy thin films excited by interrupted easy axis drive fields is investigated and correlated with the available theory of transient wall contraction. The experimental technique is useful in determining the average wall velocity, and by comparing the velocity-field curves with field duration as a parameter it is possible to infer several features of the transient behavior. It is found that, when the displacement of the wall is of the order of a characteristic distance associated with the wall coercive force interaction, the threshold field for net motion as well as the mobility of the average velocity curves depend on the field duration. The theory together with a breakable-spring model of the coercive force interaction reasonably explain the observed phenomena.

Magnetic domain wall mobility limitation by anisotropic impurity ions in ferrimagnetic insulators

A theory is given for the limitation of magnetic domain wall velocity in ferrimagnetic insulators due to the relaxation of constituent ions with anisotropic energy levels. For 10 per cent Yb 3+ doped yttrium iron garnet the predicted velocity falls from 7 × 10 5 cm sec −1 Oe −1 at 300°K to 20 cm sec −1 Oe −1 at ∼ 12°K, then rises sharply. Measurements of switching time on pure and 10 per cent doped Yb doped Y.I.G. show the impurity dominates the velocity limitation for 6°K < T < 100°K and experiment accords with theory here within the limits of the qualitative comparison. According to the theory the phenomenological damping constant determined from microwave resonance line-width and wall velocity are predicted to agree, roughly, for high but not low T for such materials. The low wall velocity observed in pure Y.I.G. receives no explanation.