磁性多孔纳米片微波磁导率的微磁学研究

本文基于微磁学理论模拟了多孔α-Fe纳米片的微波磁性能. 与无纳米孔洞的纳米片对比, 发现由于纳米孔洞的引入导致退磁能发生改变, 破坏了纳米片原有的磁畴分布, 使纳米片内部存在数目更多、体积更小、局域有效场强不同的磁畴, 从而增加了高频磁损耗峰的数目. 由于部分损耗峰的相互交叠, 为在10–30 GHz范围拓宽电磁波吸收的带宽提供了潜在可能性. 模拟结果表明多孔纳米片的磁损耗峰数目、强度、峰宽和频率分布受孔洞排布方式和孔洞数目的影响. 由于纳米孔洞的存在可以降低材料的密度, 模拟结果表明多孔α-Fe纳米片可用于开发吸收频段宽、重量轻的电磁波吸收材料.

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

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 α-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: 2×10; 2×5; 2×2; 4×5) 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 10–30 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.