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

Abstract

Measurements of the ac magnetic susceptibility of perpendicularly magnetized Fe/2 ML 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 the many local domain wall segments required to affect domain growth.PACS numbers:

Monte Carlo simulation of the effects of higher-order anisotropy on the spin reorientation transition in the two-dimensional Heisenberg model with long-range interactions

“…The authors note that near to the SRT, quadratic coupling alone is not sufficient to account for this mixed behavior. Using AC susceptibility studies of striped phases in Fe/Ni films by Abu-Libdeh et al [36,37,57], have also indicated the presence of long time scale dynamics. By varying the order of anisotropy we wish to investigate the nature of the phase transition between the striped and in plane phases.…”

Glassy behavior of two-dimensional stripe-forming systems

“…There are many reports in the literature showing metastable patterns and slow dynamics at low temperatures, which may be related with glassy physics [3,7,12,13,19,20]. Then it is important to assess the relevance of metastable states for the behavior of thermodynamic and dynamic functions.…”

“…The simplest non-trivial structure is the replica symmetric (RS) one: one associates a (static) correlation to the diagonal elements, and a (long-time) dynamic correlation to the off-diagonal ones 2,3 . The configurational entropy may then be associated to the appearance of a non-trivial matrix structure in replica space.…”

“…Competing interactions are also responsible for the appearance of complex patterns, like stripes, lamellae, bubbles and others [1]. Examples range from solid state systems, like ultrathin ferromagnetic films [2,3] and strongly correlated electron liquids [4,5], to soft matter systems like Langmuir monolayers [6], block copolymers [7,8] and colloids [9][10][11].…”

“…This is particularly dramatic in experiments, which often report effects of metastable phases and structures, although this is not always properly recognized. A few experimental results quantifying the low temperature dynamics of quasi-twodimensional stripe forming systems have been reported [3,7]. Experimental and also computer simulation results [12,13] point to the presence of slow dynamics associated with the pinning of topological defects, which are the relevant excitations at low temperatures.…”