Controle de paredes de domínio em nanoanéis de NiFe em estruturas núcleo-casca cilíndricas com acoplamento dipolar

Abstract

Nanostructured magnetic systems and their properties have gone through great achievement and still keep being focus of intense research effort nowadays. From the pure theoretical point of view, the interest focus on new magnetic phases that might emerge from dipolar effects in systems, with geometric constrictions, with dimensions of the order of tenths of fundamental magnetic lengths. There is also a large interest from the viewpoint of applications, such as magnetic sensors, nano-oscillators and new designs of magnetic memories. Motivated by recent experimental results, showing the possibility of domain wall confinement in ferromagnetic nanorings, by magnetic constrictions like notches and asymmetries, in addition to studies which reveal a strong impact of the domain wall width on the electrical resistance, we propose a new form for creating and tailoring domain walls in nanorings, by means of the magnetic dipolar interaction in cylindrical core-shell nanostructures. In this work, we show that NiFe nanorings have their magnetic pattern drastically changed when put in the presence of a coaxial Fe or NiFe nanodisk. With a Fe nanodisk as the core, we have found the formation of domain walls in NiFe nanorings that would hold magnetic vortices when isolated. Furthermore, we show that large changes in the domain wall width and domain wall patterns may be achieved by suitable choices of the core-shell geometrical dimensions. For NiFe-NiFe core-shells, we have found that the core-shell dipolar interaction affects both the core and shell phases, due to the vanishing anisotropy of NiFe.