# Magnetic Properties of NiZn Ferrite Nanofibers Prepared by Electrospinning
## 1 Introduction  
Electronic devices occupy a very important place in modern daily life and the industry. The circuits for these devices have become more portable and functional through increasingly higher levels of integration and complicated structure. Since this trend inevitably makes devices vulnerable to electromagnetic interference, there is a growing demand for simple and efficient electromagnetic wave shielding materials to prevent unnecessary wireless noise. Various studies have reported that, to achieve a thin and light shielding film, a magnetic ceramic filler is more potent than a heavy metal or pyramid-shaped shielding material. Transition metal oxides containing iron have unique electromagnetic, thermal, and mechanical properties, and various studies are underway in areas such as battery anode materials [1; 2; 3], catalyst materials [4; 5], and sensors [6; 7]. In particular, soft magnetic spinel ferrite has suitable magnetic properties for a ceramic paint filler to cope with high-frequency environments. In recent years, there have been many attempts to improve the efficiency of shielding films and some of the methods reported were as follows. Substitute various elements for the bivalent Fe sites inthe Fe\({}_{3}\)O\({}_{4}\) spinel ferrite structure [8; 9; 10; 11], control the content of substituted or doped elements [12; 13], and optimize the thickness of the shielding film [14; 15]. On the other hand, excellent characteristics of a one-dimensional structure like porosity, a large specific area, and improved charge mobility have been attracting more attention because of their potential value in various applications, such as solar cells [16; 17], photocatalysts [18; 19; 20], biosensors, and medical tissues [21; 22; 23]. Since the improved carrier mobility is considered to have an application value in the field of electromagnetic wave shielding film, several fillers with a one-dimensional nanostructure have been proposed [24; 25; 26]. To produce a one-dimensional nanostructure, methods such as hydrothermal [27; 28], template [29], and anodic oxidation [30; 31] are mainly used, and electrospinning have an advantage in that they can fabricate a uniform nanofiber rapidly even with a simple apparatus configuration [32]. At the same time, since the magnetization behavior of the material is closely related to the shielding efficiency and the use of the frequency band, many attempts have been made to control it. Research has focused not only on applying the one-dimensional nanostructure for a geometric advantage but also on optimizing the magnetic behavior by controlling the crystallite size. Some conventional studies have attempted to achieve this goal by increasing or decreasing the crystallite size or nanofiber diameter by controlling the heat treatment temperature [33; 34; 35]. NiZn ferrites are known to have high saturation magnetization and chemical stability, and attempts have been made to produce NiZn ferrite nanofibers and apply them as microwave absorbers [8; 36]. However, there are no reports on how the magnetization behavior in NiZn ferrite nanofibers can be changed by complex microstructural changes, such as diameter and crystallite size resulting from the polymer content in the electrospinning precursor solution. In this study, we fabricated NiZn ferrite nanofibers by the electrospinning method and controlled the microstructures, the crystallite size, and the nanofiber diameter, by polymer content in the precursor solution. As-spun nanofibers with a mixed composition of transition metal and polymer were calcined at suitable conditions and the calcined oxide nanofibers were investigated to explain the magnetization behavior of the nanofibers with various microstructures. The oxide nanofibers created different average diameters by controlling the polymer content, and the average diameter difference was measured by field emission scanning electron microscope (FE-SEM) image analysis.