Nanoestruturas magnéticas do tipo núcleo-casca: um estudo do impacto do campo dipolar

Abstract

Bi-magnetic anoparticles has been shown promises in several tachnological applications, such that permanent magnets, microwave generators devices, nanooscilators and magnetic record system for example. We presents a theoretical study about bi-magnetic core@shell nanoparticles consisting of high and low anisotropy ferromagnetic materials. The present work has analyzed nanoparticles with spherical and cylindrical geometries. Spherical particles can be employed as building block for high performance magnets, because can presents a expensive improvement in high energy product, (BH)max, of the system. The (BH)max is a key parameter, because it’s indicate if a material is good to permanent magnets. Our results show that (BH)maxcan be improved significantly, a particle of SmCo5 with 3.5 nm recovered by iron shell with 2.5 nm thickness can presents (BH)max thereabout 4 times great then uncovered particle. In other way, a core of the same material, with major diameter s relative thick shell there is a reduction in (BH)max that unfeasible their use in production of permanent magnets. We discuss in the present work the behavior of energy product these systems. Nanostructures with cylindrical geometries presents several applications, such that nano-oscillators and magnetic memory. In this way, know the magnetic profile and behavior of magnetization in demagnetizing process is relevant. A permalloy cylinder can, with 57.0 nm diameter and 21.0 nm height, presents along your magnetization curve, a vortex state. The inhibition of this state is relevant for some applications and can be reached with a presence of an external ring with elevated magnetic moment material. In the same way, can present vortex in magnetization curve by magnetic ring presence. We study further the magnetic states existing in magnetic ring due to magnetic dipolar interaction with a core.