Electromagnetic wave induced resonance in infinitely long and hollow square cobalt nano-prisms

Abstract

Abstract Confined metallic ferromagnetic nano-structures are desirable constituents in magnetic composites and devices for applications in telecommunications and electromagnetic wave absorption. Removing the core of these elements or substituting with non-magnetic fillers leads to immediate reduction in their weight and potential for tailoring their magnetic, dielectric and geometrical properties to enable the development of light-weight, high-frequency and efficient composites and devices. However the effect of this geometry change on the electromagnetic wave absorption and magnetic response in these hollow structures is not clear in comparison to their solid counterparts. In this article, electromagnetic wave propagation in long and hollow square cobalt nano-prisms with side lengths of 100 and 500 nm and with different wall thicknesses in the range 25–200 nm is simulated by solving the coupled system of Maxwell’s equations and the Landau–Lifshitz–Gilbert equation using the finite-difference time-domain method. The simulated dynamic magnetisation and power dissipation spectra indicated that the core of the long cobalt prisms can be removed up to wall thicknesses equal to the magnetic skin depth (about 50 nm estimated for cobalt) without significantly impacting electromagnetic wave absorption at the fundamental resonance frequencies. The simulations also revealed prominent higher frequency corner resonance modes in the small 100 nm prism with 25 nm wall thickness, but whose contribution becomes negligible with increasing prism size.