**1. Introduction**

Ceramic materials are in demand due to their growing use in energy harvesting technologies, including batteries, capacitors, and storage devices [1]. There are two types of ceramic materials, i.e.*,* traditional and advanced. The advanced ceramic material plays a significant role in the sensor and storage devices due to its high piezoelectric and resistive properties. These materials include oxides, nitrates, and carbides [2]. In these ceramics, the unique ferroelectric, electrochemical, pyroelectric, and piezoelectric properties are often useful for multiferroic research. The multiferroic materials with the simultaneous occurrence of various ferroic orders such as ferro

(electric/magnetic), antiferromagnetic (AFM), ferrotoridic, and ferroelastic play a significant role in developing new technological and device applications [3]. In the recent past, researchers are focused on device miniaturization, which satisfies the vast need to integrate the electric and magnetic properties in a material. There are a variety of coupling mechanisms between the electric and magnetic orders, but magnetoelectric (ME) coupling is crucial for future micro/nanoscale electronics, low-power memory devices, and spintronic devices [4]. The ME effect was initially studied in the Cr2O3 single-phase compound. After that, many materials such as DyMn2O5, TbMnO3, and BiFeO3 showed the ME coupling in its single-phase [5]. However, these materials restrict their practical suitability applications due to the weak coupling among the electric and magnetic order parameters and the transition temperature below the room temperature (RT). To avoid the above difficulties in the single-phase materials, many researchers have focused their study on designing the composite materials [6]. Usually, in composite, the electric and magnetic properties are intentionally improved by adding the required electric and magnetic phases. The induced ME coupling in the composite is the product property relation between the constituent phases. The relation between the magnetic and electric phases is written as [7]:

$$ME\_{\rm E} = \frac{\text{electric}}{\text{mechanical}} \times \frac{\text{mechanical}}{\text{magnetic}} \text{and } ME\_{\rm H} = \frac{\text{magnetic}}{\text{mechanical}} \times \frac{\text{mechanical}}{\text{electric}} \tag{1}$$

The origin of ME coupling in the composite may be strain, charge, and exchange bias mediated. It depends upon the coupling interaction at the magnetic and electric phase interface.

The alternative approach to study the coupling among the magnetic and electric ordering is the magnetodielectric (MD) effect. The existence of ME coupling can indirectly address through the MD effect. This phenomenon is defined as the magnetic field-controlled dielectric properties and reversely electric field-induced magnetic permeability [8]. Materials having MD characteristics are rich in physical content to take further research and its practical utilization. Usually, the signature of the MD effect can be realized by observing the anomaly of magnetic/dielectric transition in the dielectric/magnetic properties. The MD effect can be experienced experimentally by measuring the capacitance at the different external magnetic fields. The microscopic source of the MD effect can be originated from the extrinsic and intrinsic mechanisms. It solely depends on the origin of the dielectric properties of the material. According to G. Catalan, the MD effect can arise without having the dielectric and magnetic coupling in the sample [9]. The extrinsic mechanism responsible for the origin of the MD effect is the magnetoresistance and Maxwell-Wagner effect of the sample. Similarly, the intrinsic source of the MD effect originated from the magnetic field-induced dipolar switching mechanism. Hence, the existence of an intrinsic MD effect in a material indicates the possible signal of ME coupling. The realization of ME coupling is restricted by the symmetry requirements. The MD materials are fascinating due to their multiple microscopic origins and simplicity for device application. Recently, the MD coupling has been used to characterize the magnetic multipole orders and quantum criticality [10]. Therefore, it is necessary to investigate the MD coupling and the improvement of dielectric properties with the applied magnetic field.

The Aurivillius compound is composed of the perovskite layer (A*n*−1B*n*O3*n* + 1) 2− sandwich periodically between the (Bi2O2) 2+ fluorite layer. Here, n represents the number of perovskite layers present in the compound. For *n* = 4, Aurivillius compound Bi5Ti3FeO15 (BTFO) is explored theoretically using the first principle

*Structural, Magnetic, and Magnetodielectric Properties of Bi-Based Modified Ceramic Composites DOI: http://dx.doi.org/10.5772/intechopen.106569*

calculation and experimentally [11]. The BTFO compound exhibits the orthorhombic crystallographic structure with the *A2*1*am* space group at RT. BTFO undergoes the structural transition at high temperature from ferroelectric *A2*1*am* transform to paraelectric *I4/mmm* at 730°C [12]. The BTFO has dragged the wide attention of researchers due to its high ferroelectric and piezoelectric properties above the RT. The single-phase BTFO shows the weak MD coupling at RT due to the unavailability of strong magnetic ordering. So, the artificially mixing magnetic phases in the form of the composite may provide a potential path to improve both magnetic and MD coupling in the sample. The first chosen material is La0.67Sr0.33MnO3 (LSMO) to make the composite with the BTFO compound. Due to its exciting properties, i.e., high ferromagnetic ordering temperature ~370 K, colossal magnetoresistance, and high carrier spin polarization [13]. The second compound of interest is the Bi2Fe4O9 (BFO), which has a unique spin frustration due to the interaction among the Fe ions. BFO ceramic shows nearly RT multiferroic behavior due to the high AFM ordering temperatures of ~260 K [14]. Therefore, the above properties of both LSMO and BFO compounds may play a pivotal role in improving the magnetic as well as MD behavior of the composite.

In this work, we have examined the physical properties of the 0.5Bi5Ti3FeO15- 0.2La0.67Sr0.33MnO3-0.3Bi2Fe4O9 composite and compared it with the pure BTFO sample. The composite sample is synthesized by the sol–gel-modified technique and their dielectric, magnetic, and the source of MD effect are discussed. MD coupling in composite might be used as a potential candidate for MD device design.
