Sebastian Bustingorry

Pinning-Dependent Field-Driven Domain Wall Dynamics and Thermal Scaling in an Ultrathin Pt / Co / Pt Magnetic Film

Magnetic-field-driven domain wall motion in an ultrathin Pt/Co(0.45  nm)/Pt ferromagnetic film with perpendicular anisotropy is studied over a wide temperature range. Three different pinning dependent dynamical regimes are clearly identified: the creep, the thermally assisted flux flow, and the depinning, as well as their corresponding crossovers. The wall elastic energy and microscopic parameters characterizing the pinning are determined. Both the extracted thermal rounding exponent at the depinning transition, ψ=0.15, and the Larkin length crossover exponent, ϕ=0.24, fit well with the numerical predictions.

Multiscaling Analysis of Ferroelectric Domain Wall Roughness

Using multiscaling analysis, we compare the characteristic roughening of ferroelectric domain walls in Pb(Zr0.2Ti0.8)O3 thin films with numerical simulations of weakly pinned one-dimensional interfaces. Although at length scales up to L(MA)≥5  μm the ferroelectric domain walls behave similarly to the numerical interfaces, showing a simple monoaffine scaling (with a well-defined roughness exponent ζ), we demonstrate more complex scaling at higher length scales, making the walls globally multiaffine (varying ζ at different observation length scales). The dominant contributions to this multiaffine scaling appear to be very localized variations in the disorder potential, possibly related to dislocation defects present in the substrate.

Langevin simulations of the out-of-equilibrium dynamics of vortex glasses in high-temperature superconductors

We study the relaxation dynamics of flux lines in dirty high-temperature superconductors using numerical simulations of a London-Langevin model of the interacting vortex lines. By analysing the equilibrium dynamics in the vortex liquid phase we find a dynamic crossover to a glassy non-equilibrium regime. We then focus on the out-of-equilibrium dynamics of the vortex glass phase using tools that are common in the study of other glassy systems. By monitoring the two-times roughness and dynamic wandering we identify and characterize finite-size effects that are similar, though more complex, than the ones found in the stationary roughness of clean interface dynamics. The two-times density-density correlation and mean-squared-displacement correlation age and their temporal scaling follows a multiplicative law similar to the one found at criticality. The linear responses also age and the comparison with their associated correlations shows that the equilibrium fluctuation-dissipation relation is modified in a simple manner that allows for the identification of an effective temperature characterizing the dynamics of the slow modes. The effective temperature is closely related to the vortex liquid-vortex glass crossover temperature. Interestingly enough, our study demonstrates that the glassy dynamics in the vortex glass is basically identical to the one of a single elastic line in a disordered environment (with the same type of scaling though with different parameters). Possible extensions and the experimental relevance of these results are also discussed.

Thermal rounding of the depinning transition in ultrathin Pt/Co/Pt films

We perform a scaling analysis of the mean velocity of extended magnetic domain walls driven in ultrathin Pt/Co/Pt ferromagnetic films with perpendicular anisotropy, as a function of the applied external field for different film thicknesses. We find that the scaling of the experimental data around the thermally rounded depinning transition is consistent with the universal depinning exponents theoretically expected for elastic interfaces described by the one-dimensional quenched Edwards-Wilkinson equation. In particular, values for the depinning exponent β and thermal rounding exponent ψ are tested, and the present analysis of the experimental data is compatible with β=0.33 and ψ=0.2, in agreement with numerical simulations.

Growing correlations and aging of an elastic line in a random potential

We study the thermally assisted relaxation of a directed elastic line in a two-dimensional quenched random potential by solving numerically the Edwards-Wilkinson equation and the Monte Carlo dynamics of a solid-on-solid lattice model. We show that the aging dynamics is governed by a growing correlation length displaying two regimes: an initial thermally dominated power-law growth which crosses over, at a static temperature-dependent correlation length

Numerical Approaches on Driven Elastic Interfaces in Random Media

{L}_{T}\ensuremath{\sim}{T}^{3}

Out-of-Equilibrium Dynamics of the Vortex Glass in Superconductors

, to a logarithmic growth consistent with an algebraic growth of barriers. We present scaling arguments to deal with the crossover-induced geometrical and dynamical effects. This analysis allows us to explain why the results of most numerical studies so far have been described with effective power laws and also permits us to determine the observed anomalous temperature dependence of the characteristic growth exponents. We argue that a similar mechanism should be at work in other disordered systems. We generalize the Family-Vicsek stationary scaling law to describe the roughness by incorporating the waiting-time dependence or age of the initial configuration. The analysis of the two-time linear response and correlation functions shows that a well-defined effective temperature exists in the power-law regime. Finally, we discuss the relevance of our results for the slow dynamics of vortex glasses in high-

Thermal rounding exponent of the depinning transition of an elastic string in a random medium.

{T}_{c}

Effective Edwards-Wilkinson equation for single-file diffusion.

superconductors.

Universal depinning transition of domain walls in ultrathin ferromagnets

Abstract We discuss the universal dynamics of elastic interfaces in quenched random media. We focus on the relation between the rough geometry and collective transport properties in driven steady-states. Specially devised numerical algorithms allow us to analyze the equilibrium, creep, and depinning regimes of motion in minimal models. The relevance of our results for understanding domain wall experiments is outlined.