Dependence Of Domain Wall Velocity Research Articles

Magnetic properties and field-driven dynamics of chiral domain walls in epitaxial Pt/Co/AuxPt1−x trilayers

Chiral domain walls in ultrathin perpendicularly magnetised layers have a N\'{e}el structure stabilised by a Dzyaloshinskii-Moriya interaction (DMI) that is generated at the interface between the ferromagnet and a heavy metal. Different heavy metals are required above and below a ferromagnetic film in order to generate the structural inversion asymmetry needed to ensure that the DMI arising at the two interfaces does not cancel. Here we report on the magnetic properties of epitaxial Pt/Co/Au$_x$Pt$_{1-x}$ trilayers grown by sputtering onto sapphire substrates with 0.6 nm thick Co. As $x$ rises from 0 to 1 a structural inversion asymmetry is generated. We characterise the epilayer structure with x-ray diffraction and cross-sectional transmission electron microscopy, revealing (111) stacking. The saturation magnetization falls as the proximity magnetisation in Pt is reduced, whilst the perpendicular magnetic anisotropy $K_\mathrm{u}$ rises. The micromagnetic DMI strength $D$ was determined using the bubble expansion technique and also rises from a negligible value when $x=0$ to $\sim 1$ mJ/m$^2$ for $x = 1$. The depinning field at which field-driven domain wall motion crosses from the creep to the depinning regime rises from $\sim 40$ to $\sim 70$ mT, attributed to greater spatial fluctuations of the domain wall energy with increasing Au concentration. Meanwhile, the increase in DMI causes the Walker field to rise from $\sim 10$ to $\sim 280$ mT, meaning that only in the $x = 1$ sample is the steady flow regime accessible. The full dependence of domain wall velocity on driving field bears little resemblance to the prediction of a simple one-dimensional model, but can be described very well using micromagnetic simulations with a realistic model of disorder. These reveal a rise in Gilbert damping as $x$ increases.

Effect of annealing on magnetic properties and structure of Fe-Ni based magnetic microwires

We studied the magnetic properties and domain wall (DW) dynamics of Fe47.4Ni26.6Si11B13C2 and Fe77.5Si7.5B15 microwires. Both samples present rectangular hysteresis loop and fast magnetization switching. Considerable enhancement of DW velocity is observed in Fe77.5Si7.5B15, while DW velocity of samples Fe47.4Ni26.6Si11B13C2 is less affected by annealing. The other difference is the magnetic field range of the linear region on dependence of domain wall velocity upon magnetic field: in Fe47.4Ni26.6Si11B13C2 sample is considerably shorter and drastically decreases after annealing. We discussed the influence of annealing on DW dynamics considering different magnetoelastic anisotropy of studied microwires and defects within the amorphous state in Fe47.4Ni26.6Si11B13C2. Consequently we studied the structure of Fe47.4Ni26.6Si11B13C2 sample using X-ray diffraction and the atom probe tomography. The results obtained using the atom probe tomography supports the formation of the B-depleted and Si-enriched precipitates in the metallic nucleus of Fe-Ni based microwires.

Switching processes of thin ferroelectric films

The influence of size effects on dielectric and switching characteristics of lead titanate and lead zirconate titanate thin films with various thicknesses was studied. It was shown that with decreasing the film thickness the “creep” regime of domain wall movement is expanded due to shortening area where the sliding motion of domain walls occurs. In weak electric fields a deviation from the strictly exponential dependence of domain wall velocity V on the strength of an applied electric field was established with the appearance of an exponent in dependence V∼exp[−C/Eμ], where C – constant and μ – dynamic factor. For lower thicknesses of films with polycrystalline structure the values of this factor approach to unity due to an increase of the orientation of crystallite axis. For strong fields with decreasing film thickness the domain wall mobility decreases due to an increase of near-surface defect contribution to domain wall motion.

Magnetic Properties and Domain Wall Propagation in Micrometric Amorphous Microwires

We studied magnetic properties and domain propagation in thin magnetic amorphous microwires Fe72 75Co2 25B15Si10. At low metallic nucleus diameters considerable increase of switching field has been observed. Dependence of domain wall velocity, v , measured by abovementioned method shows roughly linear dependence on applied magnetic field, H, achieving about 850 m/s at 18 Oe. This velocity is somehow smaller as compared with similar microwires compositions of thicker diameter. Probably, magnetoelastic contribution plays an important role in domain wall propagation. Results are discussed taking into account the magnetoeleastic contribution.

The defects influence on domain wall propagation in bistable glass-coated microwires

We studied the domain wall (DW) dynamics of magnetically bistable amorphous glass-coated Fe74B13Si11C2 microwires. In according to our experimental results magnetic field dependences of DW velocity of studied microwires can be divided into two groups: with uniform or uniformly accelerated DW propagation along the microwire. Strong correlation between the type of the magnetic field dependence of domain wall velocity, v(H), and the distribution of the local nucleation fields has been observed.Moreover, we observed abrupt increasing of DW velocity (jump) on the magnetic field dependences of the domain wall velocity, v(H), for the both types of the v(H) dependences. At the same time usual linear increasing of the domain wall velocity with magnetic field persists below these jumps. It was found that the jump height correlates with the location of nucleation place of the new domain wall. We have measured local nucleation field distribution in all the microwires. From local nucleation field distribution we have obtained the DW nucleation locations and estimated the jump height

Study of domain wall propagation in nanostructured CoPt multilayers by using antisymmetric magnetoresistance

Domain wall propagation has been studied in perpendicular anisotropy CoPt multilayers patterned by e-beam lithography into 5 μm wide wires. Positive and negative peaks appear in time resolved magnetoresistance curves, associated to the different directions of domain wall propagation along the wires. The field dependence of domain wall velocity is well described by a creep model of a 1D wall in the presence of weak disorder with critical exponent μ=1/4.

Domain Wall Dynamics in a Double-Layer Magnetic Film with Different Uniaxial Anisotropy the Layers

Motion of an isolated domain wall in a double-layered magnetic film, whose layers differ in their uniaxial anisotropy only, is investigated through solving the Slonczewski equations by a numerical method. Dependences of the threshold field and the limiting velocity of disruption of the steady state motion of the film on the anisotropy and thicknesses of layers are obtained. Also, we showed that in domain wall unsteady motion regime, a dependence of domain wall velocity from magnetic field contains a series velocity peaks that relies on steady motion of Bloch lines across film and domain wall velocity in such cases can’t be simply increased by increasing magnetic field and restricted by some volume.

Fractal Dimensions in Switching Kinetics of Ferroelectrics

Early work by the author with Prof. Ishibashi [Scott et al., J. Appl. Phys. 64 , 787 (1988); 61 , 5467 (1987)] showed that switching kinetics in ferroelectrics, particularly lead zirconate titanate (PZT), satisfy a constraint on current transients compatible with d = 2.5 dimensionality. At that time with no direct observations of the domains, it was not possible to conclude whether this was a true Hausdorff dimension or a numerical artefact caused by an approximation in the theory (which ignored the dependence of domain wall velocity upon domain diameter). Recent data suggest that the switching dimensionality is truly fractal with d = 2.5. The critical exponent β characterizing the order parameter P(T) can be written as a continuous function of dimension d as β(d) = [ν (d)/2] [d+η(d)−2], which is exact within hyperscaling; here ν and η are the exponents characterizing the pair correlation function G(r,T) and the structure factor S(q,T). For d = 2.5 the estimate is that β is approximately 1/4.

High-drive-field domain wall dynamics in low-damping garnet films

Domain wall (DW) dynamics in a low-damping YBiFeGa film with perpendicular magnetic anisotropy was studied under FMR conditions. Measurements were carried out under radial expansion of magnetic bubbles in high pulsed drive fields and in an in-plane de magnetic field. A high-speed image recording technique was employed. The pattern of the dependence of DW velocity on drive field for the parts of the DW oriented parallel and perpendicular to the in-plane field was established. In all cases, this dependence contains a saturation region in which the DW velocity increases noticeably with increasing in-plane field. The experimental data obtained do not agree with theory. A possible explanation for this discrepancy is proposed. The onset of spatially periodic distortions in a moving DW is discussed.

Domain wall mobility in ultrathin epitaxial Ag/Fe/Ag(001) films

The dependence of domain wall velocity on applied field strength for an in-plane magnetized ultrathin epitaxial Ag/Fe/Ag(001) multilayer film has been measured using magneto-optics. Within the velocity range of 0–200 ms−1 we find a linear response, which is characteristic of viscous damping. We find a domain wall mobility value of 117±5 ms−1 Oe−1, which is comparable to that reported by other workers for high quality Fe whiskers. This shows that the Fe/Ag interfaces do not contribute substantially to the dynamic dissipation.

On a cusp in the magnetic field-velocity dependence for domain-wall motion in rare-earth orthoferrites

Using the Landau-Lifshitz equations and the equation for acoustic waves, a formula describing the steps in the dependence of domain-wall velocity v on external magnetic field H is obtained. The analysis leads to the conclusion that a 'break' can be observed in the maximum of the H(v) dependence (i.e. a jump in the differential mobility of the domain wall) caused by a change in the contribution of long-wavelength acoustic waves to the dissipation function. An approximation for the H(v) dependence describing such a jump is proposed. The possibility of the existence of a second maximum on the H(v) curve at velocities less than the speed of sound is demonstrated.

Direct overwrite in magneto-optical recording

We have used a numerical model of thermomagnetic recording to investigate direct overwrite by domain destabilization in magneto-optical thin films. Our model includes a linear dependence of domain wall velocity on the net wall pressure due to the demagnetizing field and the wall energy density. Direct overwrite by domain destabilization can be accomplished in one step, without bias fields or prior reading or erasure.

Influence of magnetoelastic interactions on domain wall motion in YFeO 3 platelets

Dependence of domain wall velocity on drive field v( H) obtained in YFeO 3 platelets cut perpendicular to the c-crystallographic axis are presented. A single flat wall parallel to the c-axis was made to move with constant velocity in different crystallographic directions. The v( H) dependence in nonlinear and changes with the direction of motion. Velocity saturates twice near velocity of transverse and longitudinal sound waves. These nonlinearities are interpreted as the result of interactions between the domain wall and elastic vibrations of the crystal. Theory of these phenomena in infinite orthoferrite crystal is presented and compared with experimental results.