Dynamics of domain growth driven by dipolar interactions in a perpendicularly magnetized ultrathin film

TL;DR

This study investigates the domain growth dynamics in ultrathin ferromagnetic films driven by dipolar interactions, revealing slow relaxation times and the influence of structural defects on domain behavior.

Contribution

It provides a quantitative analysis of how dipolar interactions govern domain growth dynamics and pinning effects in ultrathin magnetic films, highlighting the slow relaxation timescales involved.

Findings

Domain growth driven by dipolar interactions is slow, with relaxation times around 10^5 times longer than individual Barkhausen steps.

The susceptibility peak shifts with heating rate, indicating non-equilibrium domain density dynamics.

Pinning by structural defects significantly influences the response time of domain growth.

Abstract

Measurements of the ac magnetic susceptibility of perpendicularly magnetized Fe/2ML Ni/W(110) ultrathin films show a clear signature of the dynamics of domain growth and domain density changes in the striped domain pattern that this system supports. The susceptibility peak measured at different constant heating rates in the range 0.20 K/s < R < 0.70 K/s shifts to higher temperature as the heating rate is increased. Analysis using a relaxation model demonstrates quantitatively that the dynamics is driven by a non-equilibrium domain density at (nearly) zero field (i.e. by dipole interactions), and that the temperature shift is due to a response time determined by the pinning of local domain wall segments by structural defects. The fundamental time scale for relaxation of the domain density driven by dipole interactions is of order 10^5 times slower than the fundamental time scale for an individual Barkhausen step driven by an applied field. The increase in the fundamental time scale reflects the relative size of dipole and Zeeman energies, and the need for the correlated motion of many local domain wall segments to affect domain growth.