Micromagnetics simulation on the microwave permeability of magnetic porous nano-flakes

Abstract

Many modern electronic devices are operated on a frequency above 1 GHz. Frequencies of electromagnetic noises coming from these devices are usually larger than 10 GHz. High-frequency magnetic losses in the natural resonance mechanism can be used to dissipate the energy of electromagnetic noises. Ferromagnetic nanostructural materials (nano flakes or nanowires) in strong shape anisotropy fields are one of the promising anti electromagnetic interference (EMI) materials due to their large high-frequency magnetic losses. Application of EMI requires that the electromagnetic wave absorbing materials should be lightweight and have a wide absorbing bandwidth. However, most electromagnetic wave absorbing materials reported do not have these features. To meet these demands, the microwave magnetic properties of porous -Fe nano flakes (length width thickness: 300 nm 100 nm 10 nm) have been simulated based on micromagnetics theory. Compared to the nano flakes without nano pores, simulation results reveal that the demagnetization fields will be altered if a nano flake contains several pores. Effect of nano pores (diameter =15 nm) in different arrangements (rows columns: 210; 25; 22; 45) on the high-frequency magnetic properties is investigated in this paper. It is found that nano flakes can alter the configurations of magnetic domains. More domains in small sizes in an inhomogeneous localized magnetic anisotropic field have been achieved. Consequently, more high-frequency magnetic loss peaks can be found. Overlapping of magnetic loss peaks implies that it potentially enables to widen the bandwidth of electromagnetic absorption within 1030 GHz. Furthermore, simulations reveal that the quantity, magnitude and resonance frequencies of the loss peaks are strongly dependent on the quantity and the arrangement of nano pores. Besides, the existence of multi magnetic loss peaks has been studied for ellipsoid objects from the perspective of inhomogeneously localized effective magnetic fields. Results reveal that the frequently observed wide magnetic loss peaks in experimental data may be due to the inhomogeneously localized effective magnetic fields of an absorber containing a plentiful of randomly oriented particles. Clearly, compared to the nano flakes without pores, the nano flakes with pores can significantly reduce the volume density. Therefore, our simulation results show that porous nano flakes can be a good lightweight electromagnetic wave absorber candidate with wide absorbing bandwidths.