In this study, I simulate domain wall dynamics and Barkhausen noise in ferromagnetic thin films with the random-field Ising model. Barkhausen noise is a phenomenon that has been studied for almost a century yet the theory remains unclear in ferromagnetic thin films. The noise is mainly generated by the irregular movement of the magnetic domain walls, which separate the magnetic domains with different uniform magnetizations. Barkhausen noise is observed as the jerky variations of the magnetization as a pinned domain wall abruptly advances and causes an avalanche.
The simulations of this work focus on the thin films, which previously have been studied with various simulations and some experiments. The random-field Ising model is a spin model which has a quenched random field interacting with the spins. In this study, also the dipolar interactions are introduced to the system. The competition between the exchange interactions of quantum mechanical origin and the dipolar interactions force the domain wall to create zigzag patterns. I simulate the model with triangular, square and hexagonal lattices.
The results show the effect of the underlying lattices on the domain wall dynamics and structure. Universality of the Barkhausen effect would implicate that the microstructural parameters such as the lattice structure of the model should not affect the universality classes. The extensive simulations on the hexagonal lattice reveal the power law behavior of the avalanche size distributions as the strength of the dipolar interactions and the random field are varied. Square and triangular lattices form high amplitude zigzag patterns due to the dipolar interactions.
