## 1 Introduction  
With the rapid propagation of the electronic devices--especially personal mobile phones, satellite communication, radar detectors, and other communication devices--electromagnetic waves (EMW), taken as \"pollution\", are growing to be a huge threat to human health and has been attracted consideration attention [1]. Thus, great efforts have been devoted to exploiting the electromagnetic absorption (EMA) materials with low mass density, ultra-thin, and high EMA performance to eliminate the superfluous EMWs [2; 3; 4]. In the past decades, metal powders [5], graphite [6], and ferrites [7; 8] were the mainstream materials in the field of the EMA materials. However, there are several drawbacks existed in these traditional EMA materials, such as high weight, narrow bandwidth, and unsatisfactory microwave absorption performance, have seriously hindered their practical applications. Nowadays, the carbon-based nanomaterials--such as multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO),and carbon black--have been given highly attention in the field of aerospace engineering [9; 10; 11; 12]. Particularly, rGO, as one of the most promising carbon-based nanomaterials, is commonly used as a high dielectric material. Because it possesses several excellent characteristics such as being lightweight, and having high specific surface area and abundant surface defects (such as diverse oxygen-containing groups) as well as its excellent mechanical properties. Even so, in terms of EMA impedance principle, pure rGO still is insufficient for impedance matching due to the limitation of single dielectric loss behavior [10; 13; 14]. Therefore, several scholars have focused on how to adjust the composition of nanomaterial to optimize their electromagnetic (EM) parameters, so as to achieve excellent microwave attenuation. For example, [PERSON] et.al reported the chemical reduction process of rGO by ascorbic acid (VC). It was suggested that the degree of lattice defects in rGO could be tuned by the increase of VC addition, which could significantly enhance the EMA performance [15]. [PERSON]'s group also reported that the nitrogen-doped rGO sheet exhibited the excellent EMA performance in the G band (5.6-8.2 GHz) and X band (8.2-12.4 GHz) due to the existence of the lattice defects in nitrogen-doped rGO [16]. Except for optimizing EM parameters by tuning the degree of defects in rGO, rGO combined with other magnetic loss materials, such as, CoNi [13], CoFe\({}_{2}\)O\({}_{4}\)[17; 18], FeCo [18], Fe\({}_{3}\)O\({}_{4}\)[19], and Fe@Fe\({}_{3}\)O\({}_{4}\)[20], is also a meaningful way to control the EMA performance. Particularly, when the magnetically controlled Fe\({}_{3}\)O\({}_{4}\) nanoparticles are directly packaged on the rGO sheet, these results contribute to optimizing the impedance matching and enhance the EMW attenuation [21; 22]. Random Fe\({}_{3}\)O\({}_{4}\) nanoparticle packaging can be difficult to predict, thus making it difficult to obtain composite behavior at a large scale [23; 24]. Meanwhile, this charge transfer between rGO and magnetic lossy materials can easily generate the interfacial polarization, dipole relaxation, and magnetic loss [25; 26]. In general, thermoplastic polymer matrices play an important role in the EMA composites due to their excellent mechanical properties [27; 28]. Meanwhile, several interfacial effects or synergetic effects have been constantly occurred between the nano-fillers and thermoplastic polymer matrices, which are available for the enhancement of EMA performance of the absorbers [29; 30]. Poly(vinylidene fluoride-\(co\)-hexafluoropropylene) (PVDF-\(co\)-HFP), as a typical dielectric loss material, has been widely applied in the various fields owning to its unique dielectric properties, high mechanical stability and excellent chemical resistance [31; 32]. Herein, the fabrication process of two types of Si-modified rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-\(co\)-HFP composites was investigated (Scheme 1).