Abstract
Amorphous Fe64Gd36 thin film square elements are investigated by imaging in the Fresnel mode of a transmission electron microscope (TEM). The equilibrium state without an applied field shows the well-known four-domain flux closure pattern with in-plane magnetization. However, the vortex is displaced from the center of the square element and the domain walls are curved. In a reference measurement of a thin Ni81Fe19 element, the vortex core is perfectly centered and the domain walls straight. When an increasing external field is applied in-plane, the vortex core can be moved. While this motion of the vortex core is linear in NiFe elements, in the ferrimagnetic FeGd squares the vortex core moves by sudden jumps. Micromagnetic simulations show that the asymmetry of the domain patterns as well as the vortex core pinning and depinning can be attributed to random anisotropy and a patchy microstructure in amorphous films.
Highlights
In patterned ferromagnetic thin film elements multidomain states form if the elements are sufficiently large
In medium sized square elements the remanent state is a four-domain pattern with straight domain walls and a center vortex.[1]
Dietrich and co-workers[2] showed that in permalloy (Ni81Fe19) squares a distorted flux closure pattern may arise from the substrate curvature which may lead to curved domain walls
Summary
In patterned ferromagnetic thin film elements multidomain states form if the elements are sufficiently large. Most commonly the ground state is a symmetric flux closure pattern. In medium sized square elements the remanent state is a four-domain pattern with straight domain walls and a center vortex.[1] Dietrich and co-workers[2] showed that in permalloy (Ni81Fe19) squares a distorted flux closure pattern may arise from the substrate curvature which may lead to curved domain walls. The magnetic field created by the tip of a magnetic force microscope can induce twisted flux closure patterns.[3] A distortion of the equilibrium domain patterns caused by magnetic fields was reported by Hertel and co-workers.[4] They showed that the demagnetizing field of nano-islands with inclined surface leads to asymmetric magnetic states
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