Nucleação de paredes de domínio e produto energético máximo em nanocilindros magnéticos tipo Núcleo@Casca

Abstract

Ferromagnetic structures in confined geometries have attracted great interest, as geometric confinement opens new routes for manipulating fundamental magnetic properties required by major applications such as logic devices, magnetic sensors, nano-oscillators and magnetic memories. We report a theoretical study of the impact of dipolar interaction on the magnetic phases of the core@shell rectangular nanocylinders. Our results indicate that the dipolar interaction between the core and the shell is capable of causing significant changes in the magnetic phases of the isolated iron (Fe) cylinder and the Ni80Fe20 alloy ring, known as Permalloy (Py). We show that the geometric parameters of flat Fe@Py core@shell cylinders can be chosen in such a way to control the nucleation of domain walls in the Py shell. It is also possible to fine-tuning the domain wall position and width by using only magnetic energies. On the other hand, bimagnetic nanoparticles combining different functionalities of two magnetic materials opens new perspectives for key applications such as permanent magnets, recording media, and magnetic hyperthermia. A theoretical analysis of the impact of the composition of FePt@CoFe2 and FePt@Fe bimagnetic nanocylinders on the maximum energy product (BH)max was performed. (BH)max is the determining parameter of the permanent magnet quality. The best composition is determined by the competing trends imposed by the dipolar energy and a ferromagnetic core@shell interface exchange energy. It was observed that the dipolar interaction has a negative impact on the intensity of (BH)max for shell thicknesses above a theresehold value, which depends on the material. The results show that the best shell material is the one with highest exchange stiffness.