Measuring the roughness exponent of magnetic domain walls in disordered media

DANIEL JORDÁN; SEBASTIÁN BUSTINGORRY; MARÍA JOSÉ CORTÉS BURGOS; MARA GRANADA; PAMELA C. GURUCIAGA; LUCAS J. ALBORNOZ; JAVIER CURIALE

Buenos Aires

Congreso; 27th International Conference on Statystical Physics; 2019

Departamento de Física, FCEyN-UBA

A wide variety of interfaces occurring in nature needs to be described by their roughness, i.e. by the fluctuations of the interface´s position. Although many alternative definitions exist for the roughness, they all present self-affinity as a result of scale invariance. In other words, the roughness evolves with a characteristic length scale $L$ as $A*L^{zeta}$, with $A$ the roughness amplitude and $zeta$ the roughness exponent. The relevance of the roughness exponent relies on that it permits one to classify the interfaces in different universality classes. In particular, for magnetic domain walls the roughness exponent can be directly related to the different static and dynamics regimes, and thus the importance to measure it.In this work, we study the roughness of domain walls in magnetic thin films with perpendicular anisotropy under the effect of out-of-plane and in-plane magnetic fields. Experimentally, we achieve this by means of polar magneto-optical Kerr effect (PMOKE) microscopy. We also numerically analyze the geometry of the domain walls generated by a simple scalar-field model, which has already been used to simulate quasi-bidimensional systems with perpendicular anisotropy and quenched disorder. We discuss the importance of making a statistical evaluation of both the roughness exponent $zeta$ and roughness amplitude $A$, and show that our intuitive understanding of roughness is enclosed in the amplitude rather than the exponent. What is the corresponding universality class for the obtained values of the roughness exponent is a question that remains open.