We report a comparative study of magnetic field driven domain wall motion in thin films made of different magnetic materials for a wide range of field and temperature. The full thermally activated creep motion, observed below the depinning threshold, is shown to be described by a unique universal energy barrier function. Our findings should be relevant for other systems whose dynamics can be modeled by elastic interfaces moving on disordered energy landscapes.

PACS 64.60.Ht -Dynamic critical phenomena PACS 75.60.Ch -Domain walls and domain structure PACS 05.70.Ln -Nonequilibrium and irreversible thermodynamicsAbstract. -We study thermal effects at the depinning transition by numerical simulations of driven one-dimensional elastic interfaces in a disordered medium. We find that the velocity of the interface, evaluated at the critical depinning force, can be correctly described with the power law v ∼ T ψ , where ψ is the thermal exponent. Using the sample-dependent value of the critical force, we precisely evaluate the value of ψ directly from the temperature dependence of the velocity, obtaining the value ψ = 0.15 ± 0.01. By measuring the structure factor of the interface we show that both the thermally-rounded and the T = 0 depinning, display the same large-scale geometry, described by an identical divergence of a characteristic length with the velocity ξ ∝ v −ν/β , where ν and β are respectively the T = 0 correlation and depinning exponents. We discuss the comparison of our results with previous estimates of the thermal exponent and the direct consequences for recent experiments on magnetic domain wall motion in ferromagnetic thin films.

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.