Domain Wall Speed Research Articles

Fast domain wall motion in nanostripes with out-of-plane fields

Controlling domain wall motion is important due to the impact on the viability of proposed nanowire devices. One hurdle is slow domain wall speed when driven by fields greater than the Walker field due to nucleation of vortices in the wall. We present simulation results detailing the dynamics of these vortices including the nucleation and subsequent fast ejection of the vortex core leading to fast domain wall speeds. The ejection is due to the reversal of the core moments by an out-of-plane field. The technique can be used to produce domain walls of known orientation, independent of the initial state.

Enhanced domain wall speed in non-c-oriented SrBi2Ta2O9 thin film

A non-c-oriented SrBi2Ta2O9 thin film was fabricated by eclipse pulsed laser deposition. It showed improved ferroelectric properties as well as enhanced domain wall speed. The enhanced domain wall speed directly indicates that the non-c-oriented domain has a lower activation field in terms of Merz's law than the highly c-oriented domain. The non-c-oriented domains of the low activation field give easier domain switching with the fast domain wall speeds than the c-oriented domains.

Domain wall motion in epitaxial Pb(Zr,Ti)O3 capacitors investigated by modified piezoresponse force microscopy

We investigated the time-dependent domain wall motion of epitaxial PbZr0.2Ti0.8O3 capacitors 100nm thick using modified piezoresponse force microscopy (PFM). We obtained successive domain evolution images reliably by combining the PFM with switching current measurements. We observed that domain wall speed (v) decreases with increases in domain size. We also observed that the average value of v, obtained under applied electric field (Eapp), showed creep behavior, i.e., ⟨v⟩∼exp[−(E0∕Eapp)μ] with an exponent μ of 0.9±0.1 and an activation field E0 of about 700kV∕cm.

Magnetic domain wall creep in the presence of an effective interlayer coupling field

We investigate thermally activated domain wall creep in a system consisting of two ultrathin Co layers with perpendicular anisotropy coupled antiferromagnetically through a 4 nm thick Pt spacer layer. The field driven dynamics of domain walls in the softer Co layer have been measured while keeping the harder Co layer negatively saturated. The effect of the interlayer interaction on the soft layer is interpreted in terms of an effective coupling field, H J , which results in an asymmetry between the domain wall speeds measured under positive and negative driving fields. We show that creep theory remains valid to describe the observed wall motion when the effective coupling field is included in the creep velocity law as a component of the total field acting on the wall. Using the resultant modified creep expression, we determine a value for the effective coupling field which is consistent with that measured from the shift of the soft layer's minor hysteresis loop. The net antiferromagnetic coupling is attributed to a combination of RKKY and orange-peel coupling.

Enhancing domain wall speed in nanowires with transverse magnetic fields

Dynamic micromagnetic simulation studies have been completed to observe the motion of a domain wall in a magnetic nanowire in an effort to increase the field-driven domain wall speed. Previous studies have shown that the wire dimensions place a cap on the maximum speed attainable by a domain wall when driven by a magnetic field placed along the direction of the nanowire. Here we present data showing a significant increase in the maximum speed of a domain wall due to the addition of a magnetic field placed perpendicular to the longitudinal driving field. The results are expressed in terms of the relative alignment of the transverse field direction with respect to the direction of the magnetic moments within the domain wall. In particular, when the transverse field is parallel to the magnetic moments within the domain wall, the velocity of the wall varies linearly with the strength of the transverse field increasing by up to 20%. Further examination of the domain wall structure shows that the length of the domain wall also depends linearly on the strength of the transverse field. We present a simple model to correlate the effects.

Supersonic domain wall in magnetic microwires

Here, we present experimental evidence for the very fast domain wall in microwires that can reach wall-motion velocity approaching $18.5\phantom{\rule{0.3em}{0ex}}\mathrm{km}∕\mathrm{s}$, which is much higher than the sound velocity in the magnetic wires. We show that the domain wall speed can be adjusted by counterbalancing between the longitudinal magnetic anisotropy leading to small damping and the strong transversal anisotropy.

Simulating the Maximum Domain Wall Speed in a Magnetic Nanowire

The dynamics of domain wall motion in permalloy nanowires have been simulated utilizing the Landau-Lifshitz-Gilbert (LLG) equation of motion. The simulation results are presented in terms of the domain wall speed for ranges of the Gilbert damping parameter alpha and nanowire width. The maximum domain wall speed is independent of alpha. The speed of the domain wall can be increased by increasing the nanowire width, but this lowers the critical field. For applied fields below the critical field, the wall moves uniformly along the wire and the speed of the wall increases with increases in the driving field. This behavior is consistent with current analytic models; however, the models overestimate both the value of the domain wall speed and the critical field

Simulated domain wall dynamics in magnetic nanowires

The simulated domain wall dynamics in rectangular 10nm thick, 2000nm long Permalloy wires of varying width is presented. In the absence of an applied field the static domain wall length is found to be linearly dependent to the width of the nanowire. As magnetic fields of increasing strength are applied along the wire’s long axis, the domain wall motion changes from a uniform reversal to a steplike reversal. The onset of the stepping motion leads to a decrease in the domain wall speed. By continuing to increase the field it is possible to decrease the time between steps increasing the domain wall speed. The critical field associated with the crossover from uniform to nonuniform reversal decreases as the wire width increases.

Field sweep rate dependence of domain-wall speed distributions in a thin Ni80Fe20 film

The magnetization reversal in a thin (100nm) Ni80Fe20∕GaAs(001) film prepared by molecular-beam epitaxy has been investigated using a focused spot Kerr magnetometer. The field was sinusoidal and applied along an in-plane easy axis, with sweep rate at the coercive point in the range ∼1kOe∕s–1MOe∕s. Real time measurements of the Kerr response enabled a study of the probability distributions P(V) of the domain-wall speed as a function of sweep rate. The shape of P(V) changes from being characteristic of stochastic domain-wall motion at low sweep rate to being characteristic of quasicontinuous domain-wall motion at high sweep rate. Increasing the diameter of the focused spot from 2to80μm increases the number of domain walls participating in the reversal within the probed area, which leads to an averaging effect and dulls the transition from stochastic to quasicontinuous wall motion seen in the probability distributions.

Real time magnetisation reversal dynamics in epitaxial Fe/GaAs(001)

Time resolved Kerr microscopy has been used to investigate the magnetisation reversal dynamics in thin (50 nm) epitaxial Fe/GaAs(001). Real time measurements of the magnetic switching in a 10 μm-diameter spot on the Fe film surface have been made at selected values of sinusoidal applied field frequency f in the range 0.3–30 kHz, and distributions of coercive field H c and domain wall speed parameter have been generated in each case. The Kerr response indicates that at low-field sweep rates ( f<3 kHz) domain walls jump in a random fashion between pinning sites, whilst at higher sweep rates ( f≈3 kHz) they are driven quasi-continuously through the laser spot. As f is increased, the distribution of coercive fields becomes more sharply peaked about the mean. This is consistent with the observation of discontinuous Barkhausen-like domain wall jumps at low-field sweep rates and field-driven, quasi-continuous switching at high sweep rates. On the scale of individual domain wall movements, the probability distribution of the wall speed parameter remains strongly skewed towards lower values even at high f, indicating that stochastic behaviour persists. This emphasises that the Kerr response is dictated by probe size and can give direct information on individual reversal events only down to the spatial resolution limit.

Domain wall speed measurement of Si-Fe samples at 50 Hz magnetisation from dynamic SEM images

The use of dynamic domain images obtained from a scanning electron microscope in the measurement of domain wall velocity in Si-Fe samples is described. Results are shown demonstrating the behaviour of the domain walls during motion and when pinning occurs.

Domain wall dynamics in ultrathin Au/Co/Au films

We report on the first direct measurements of the domain wall speed and nucleation rate in ultrathin magnetic films with perpendicular anistropy. Nucleation process becomes dominating over the domain wall motion in higher fields, leading to changes in relaxation magnetization curve. The influence of the sample thickness is briefly discussed.

Eddy current losses in magnetic sheet with simple bar-like 180° domain structures

The eddy current losses in thin magnetic sheets have finite width (W), thickness (d) and simple bar-like domain structures are calculated numerically assuming sinusoidal time variation of flux and uniform domain wall speeds. The Pry and Bean values for the ratio of calculated eddy current loss (Pe) to its classical value (Pc) are attained for fixed domain width (2L) in the limit W→∞. For a fixed number of domains (N) it is found that Pe/Pc has essentially the Pry and Bean value for 2L/d≳2 if N is odd (half-size end domains). With decreasing domain width, Pe/Pc decreases monotonically and, for fixed N (odd or even), tends to zero as 2L/d→0.