Role of structural correlation with lattice dynamics in AFeO3 (A= Pr, Ga) multiferroic materials

Abstract

This chapter gives a brief introduction to the field of Cr-substituted rare-earth orthoferrites and its importance in science and technology. The inclusion of different chemical elements at different sites results in distortion of the perovskite structure away from the ideal cubic structure. A review of Fe site substitution in orthoferrites is presented and a justification for the dopant and parent compounds, which have been selected for the present work, is given in this chapter. In “Silicon Age,” silicon transistors form the core of much of the microelectronics and from the last few decades, the properties of silicon devices have been investigated to an astonishing extent, which enables the transformation of bulky old desktop computers into sleek smartphones[1–4]. But this revolution will soon be forced to come to culminate as the fundamental physical limits set by the size of the atoms that make up the silicon material. Therefore, the steady march toward smaller, faster, lighter products with more functionality can’t continue within our existing framework. The use of microelectronics is increasing worldwide so rapidly that may consume more than half of the world’s energy by information technologies within a couple of decades[1–3]. In order to improve and maintain the global standard of living, we need new multifunctional materials. Further, the demands of high performance and multitasking micro-electronic devices that can store and share information in an easier and faster way motivate scientists for searching the new materials with multi-functional properties for reading, writing and data sharing processes[2,3]. The new emerging technology “Spintronics”, which explores the control of the magnetic (spin) state by electric fields and/or vice versa can solve this problem[2,3,5–7]. Such approaches relies on exploiting the intrinsic spin of electron in addition to the electronic charge to encode the information[2,3,5–7]. The coexistence of magnetization and electric polarization may allow an additional degree of freedom for next-generation electronics devices such as solid-state transformers, high sensitively dc and ac magnetic field sensors, electrically tuneable microwave filters, and electromagnet optic actuators[2,3,5–7]. As technology advances, the increasing need for data storage and advancement in miniaturization suggest an end to the era of conventional data storage techniques[8–10]. To overcome this upcoming crisis, modern technology is emerging as a solution these days. It is worth noting here that the efficiency of conversion of primary energy (coming from natural gas, burning coil or nuclear power plants) is around 35-40% and most of the (10-15%) primary energy is consumed by the electronic devices[11]. This consumption is expected to be growing exponentially in the next few years, putting more stress on our resources for energy production[11]. To overcome this issue, we need new materials or new emerging technology as an alternate solution to this problem[2,3,5–7]. The searches for new materials for various electronic applications have dominated the research worldwide particularly after the development of silicon-based tiny integrated circuits. The tiny as well as energy efficient electronic devices are now dominating the research worldwide and replacing the conventional electronic circuit elements. The efforts are now being made to develop spin-based electronic devices and in these directions perovskite oxides are of great interest[3,5,6,12]. The perovskite type oxides are very popular and are being investigated due to their interesting underlying physics[13–16] as well as technological importance[17–20]. Indeed, the complex and unusual properties have been observed in these perovskite oxides due to the presence of strong coupling between the electric charge, spin, and lattice degrees of freedom. One of the intriguing properties shown by these transition metal oxides is their multiferroic (MF) behavior i.e. exhibit coexistence of at least two primary ferroic orders (amongst ferroelectric, ferromagnetic and ferroelastic orderings) in a single-phase compound. These materials become attractive as they can have intrinsically combined magnetic, ferroelectric, and elastic properties. In MF, the magnetism and the ferroelectricity can occur independently or may have a strong coupling between these ferroic orders. Depending upon the said coupling multiferroics are divided into two groups, which can be categorized as type-I and type-II multiferroics. The type-I MF covers those materials in which magnetism and ferroelectricity have a different origin and appears independently of one another, though there may be a little (weak) coupling between them, while type-II multiferroics exhibit strong coupling between ferroelectric and magnetic orders[3]. The interaction between two ferroic orders in these materials would result into control of electric polarization with the application of applied magnetic field or in magnetization control of electric field[21]. Broadly, in type-I multiferroics, the transition temperature of ferroelectric ordering (TFE) is generally higher as compared to that of the magnetic ordering (TM) whereas TFE and TM are same in case of type-II MF’s. There is a quest for searching the materials that exhibit such kind of coupling near to room temperature (RT), which further increases the possibility of scheming RT based novel MF devices[2,3].