Magnetic Materials

**3**

**Chapter 1**

*and Guolong Tan*

**Abstract**

measurement

**1. Introduction**

Structural, Electrical, and

*Poorva Sharma, Ashwini Kumar, Jingyou Tang* 

this material very useful in technology and practical applications.

fuel cell, scintillators and photocatalyst [3–7].

**Keywords:** multiferroic, Bi2Fe4O9, Raman spectroscopy, ferroelectric, magnetic

Multiferroic materials exhibit more than one primary ferroic order parameters (i.e. ferroelectricity, ferroelasticity and ferromagnetism) in same phase which was first proposed by Schmid in 1994 [1]. In recent years, there has been a strong interest in systems that exhibit convergence between magnetic degrees of freedom, electronic degrees of freedom, and orbital degrees of freedom. Perovskite based oxides have attracted much attention due to their interesting structural, magnetic, optical and electronic properties [2]. A large number of publications have been devoted to multiferroic materials working with theory, experimentation and application features. Bismuth-based complex oxides (Bi2Fe4O9) with mullite-type structure, as an important active material, has a wide application prospect in the fields of magnetic recording media, sensor, magnetoresistive devices, solid oxide

The crystallographic structure of Bi2Fe4O9 is orthorhombic with space group *Pbam*, No. 55, which belongs to the mullite-type crystal structure family [8, 9].

Mullite-Type Ceramic: Bi2Fe4O9

This work reports the structure, electrical and magnetic properties of the orthorhombic (*Pbam*) structured bulk Bi2Fe4O9 synthesized by the solid-state reaction process. Bi2Fe4O9 has been studied using several experimental techniques such as X-ray diffraction, scanning electron microscopy, Raman spectroscopy, dielectric spectroscopy, and magnetometry. Rietveld-refined X-ray diffraction data and Raman spectroscopy results clearly reveal the formation of Bi2Fe4O9 perovskite structure and all the peaks of Bi2Fe4O9 perfectly indexed in the orthorhombic (*Pbam*) structure. It has been established that the Raman spectrum identified Ag, B2g, and B3g active optical phonon modes, and that the Raman peak at 470 cm−1 may have a magnetic origin. As a result, the coexistence of weak ferromagnetic and antiferromagnetic orders in Bi2Fe4O9 ceramic was established. The remanent magnetization (2*M*r) and coercivity (2*H*c) are 8.74 × 10−4 emu/g and 478.8 Oe, respectively. We report a remarkable multiferroic effects in polycrystalline Bi2Fe4O9 ceramic. These characteristics make

Magnetic Properties of
