Excess velocity of magnetic domain walls close to the depinning field

TL;DR

This study investigates the behavior of magnetic domain walls in [Co/Ni] multilayers near the depinning field, revealing an unexpected excess velocity explained by a phenomenological scaling model.

Contribution

It introduces a phenomenological model that accurately describes the excess velocity of domain walls near the depinning transition in magnetic multilayers.

Findings

Universal creep regime observed at low fields

Excess velocity near depinning field identified

Model fits data and extracts depinning parameters

Abstract

Magnetic field driven domain wall velocities in [Co/Ni] based multilayers thin films have been measured using polar magneto-optic Kerr effect microscopy. The low field results are shown to be consistent with the universal creep regime of domain wall motion, characterized by a stretched exponential growth of the velocity with the inverse of the applied field. Approaching the depinning field from below results in an unexpected excess velocity with respect to the creep law. We analyze these results using scaling theory to show that this speeding up of domain wall motion can be interpreted as due to the increase of the size of the deterministic relaxation close to the depinning transition. We propose a phenomenological model which allows to accurately fit the observed excess velocity and to obtain characteristic values for the depinning field $H_d$, the depinning temperature $T_d$, and the characteristic velocity scale $v_0$ for each sample.