Materials thought-provoking physics involved and as they

Materials which are simultaneously (ferro)magnetic and ferroelectric, and often also ferroelastic, fascinate now considerable attention, both because of the thought-provoking physics involved and as they have potential in using important practical applications. A ferroelectric crystal demonstrates a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few ‘multiferroic’ materials that show both of these properties, but the ‘magnetoelectric’ coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, There has been a recent revival of interest driven by long-term technological aspirations.IntroductionA ferroic is a material that adopts a spontaneous, switchable internal alignment: In ferromagnetics, the arrangement of electron spins can be interchanged by a magnetic field; in ferroelectrics,electric dipole-moment arrangement can be switched by an electric field; and in ferroelastics, strain arrangement can be switched by a stress field. Individually, the ferroics are already of great attention both for their basic physics and for their technological applications. For example, electrical polarization in ferroelectrics and magnetization in ferromagnets are exploited in data storage, with opposite alignments of the polarization or magnetization representing “1” and “0” data bits 1. A multiferroic combines any two or more of the primary ferroic orderings in the same phase,1 such as the ferroelectric ferroelastics that form the basis of piezoelectric transducers. “multiferroic” primarily to materials that combine ferroelectricitywith ferromagnetism or, more loosely, with any kind of magnetism. The terms is often extended to comprise composites, such as heterostructures of ferroelectrics interlayered with magnetic materials. One of the most attractive aspects of multiferroics is their so-called magnetoelectric coupling. Whereas a ferroic property is usually improved using its conjugate field (magnetic fields modify magnetization, electric fields modify polarization, and so on), in a multiferroic a magnetic field can tailor the electric polarization and an electric field can tune the magnetization. That is intriguing from a basic physics point of view: Since magnetization, denoted by an axial vector, and polarization, represented by a polar vector, have different symmetry properties, it is not immediately obvious that one should be addressable by the other’s conjugate field. In terms of applications, the prospect of electric-field control of magnetism is particularly exciting, as it could lead to smaller, more energy-efficient devices for magnetic technologies 2. Indeed, the development of multiferroics during the 1970sand 1980s—spearheaded by the group of Hans Schmid in Geneva and funded, curiously enough, by the Swiss Post Office—was intimately linked to the development of the magnetoelectric effectFigure 1.Interactions In Multiferroic Ceramic MaterialsSymmetry: The ferroic properties are closely related to symmetry and can be characterized by their performance under space inversion and time reversal (see table). The operation of space inversion reverses the direction of polarization P while leaving the magnetization M invariant. As a result ferromagnets and ferroelastics are invariant under space inversion whereas ferroelectrics are not. The operation of time reversal, on the other hand, changes the sign of M, while the sign of P remains invariant. Therefore ferroelastics and ferroelectrics are invariant under time reversal whereas ferromagnets are not.Space InvariantSpace variant Time invariant Ferroelastic FerroelectricTime variantFerromagneticMagnetoelectricMultiferroicClassification: Many multiferroics are transition metal oxides with perovskite crystal structure. They can be generally subdivided into two classes as introduced by D. Khomskii: Type-I and type-II multiferroics 3. Type-I multiferroics which have been known for a long time are often good ferroelectrics and antiferromagnetic. They exhibit high ferroelectric and lower magnetic ordering temperatures. Examples are BiFeO3 (TC = 1100 K, TN = 643 K) and YMnO3 (TC = 914 K, TN = 76 K) and probably BiMnO3 and PbVO3. Since ferroelectricity and magnetism develop independently from another, the magnetoelectric coupling between the two is usually weak. In a first approach, they might be regarded as ferroelectrics which happen to be (antiferro)magnetic. However, more recently there have been reports of large magnetoelectric coupling at room-temperature in type-I multiferroics such as in the “diluted” magnetic perovskite (PbZr0.53Ti0.47O3)0.6–(PbFe1/2Ta1/2O3)0.4 (PZTFT) in certain Aurivillius phases, and in the system (BiFe0.9Co0.1O3)0.4-(Bi1/2K1/2TiO3)0.6 (BFC-BKT). Here, strong ME coupling has been observed on a microscopic scale using PFM under magnetic field among other techniques.141516 The latter system, appears to be the first reported core-shell type relaxor ferroelectric multiferroic, where the magnetic structure in so-called “multiferroic clusters” is proposed to be due Fe-Co ferrimagnetism, which can be switched by an electric field. Type-II multiferroics include rare-earth manganites such as TbMnO3, HoMn2O5. Here, magnetism causes ferroelectricity and ordering temperatures are usually identical, which are, however, at very low temperatures (e.g. 28 K in case of TbMnO3). Moreover, they exhibit low net magnetization due to antiferromagnetic spin-spiral structures and low polarization of the order of 10?2 ?C/cm2. Other, non-perovskite multiferroic oxides include LuFe2O4 and LiCu2O2 and non-oxides such as BaNiF4 and spinel chalcogenides, e.g. ZnCr2Se4. These compounds show rich phase diagrams combining different ferroic orders in separate phases.Apart from single phase multiferroics, composites and heterostructures exhibiting more than one ferroic order parameter are studied extensively. Some examples include magnetic thin films on piezoelectric PMN-PT substrates and Metglass/PVDF/Metglass trilayer structures. Besides scientific interest in their physical properties, multiferroics have potential for applications as actuators, switches, magnetic field sensors or new types of electronic memory devicesSynthesis: Multiferroics properties can appear in a large variety of materials. Therefore, several routes for conventional material fabrication are being applied. Popular techniques within the multiferroic community are: solid state synthesis., hydrothermal synthesis, sol-gel processing, vacuum based deposition, and floating zone. However some types of multiferroics require specific processing conditions within certain techniques. For instance: ? Vacuum based deposition (for instance: MBE, PLD) for thin film deposition to exploit certain advantages that may come with 2-dimensional layered structures such as: strain mediated multiferroics, heterostructures, anisotropy. ? High pressure solid state synthesis to stabilize metastable or highly distorted structures as for example lone pair multiferroics like Bi based multiferroics due to their low melting point.Applications: Multiferroic composite structures in bulk form are explored for high-sensitivity ac magnetic field sensors and electrically tunable microwave devices such as filters, oscillators and phase shifters (in which the ferri-, ferro- or antiferro-magnetic resonance is tuned electrically instead of magnetically) 4. In multiferroic thin films, the coupled magnetic and ferroelectric order parameters can be exploited for developing magnetoelectronic devices. These include novel spintronic devices such as tunnel magnetoresistance (TMR) sensors and spin valves with electric field tunable functions. A typical TMR device consists of two layers of ferromagnetic materials separated by a thin tunnel barrier (~2 nm) made of a multiferroic thin film 5. In such a device, spin transport across the barrier can be electrically tuned. In another configuration, a multiferroic layer can be used as the exchange bias pinning layer. If the antiferromagnetic spin orientations in the multiferroic pinning layer can be electrically tuned, then magnetoresistance of the device can be controlled by the applied electric field. One can also explore multiple state memory elements, where data are stored both in the electric and the magnetic polarizations.Figure 2.Magnetic Field vs. Magnetization of BFOList of Multiferroic Ceramic Materials:There are few known materials who shows the property specially oxides od transition metals. The list is given below:CrystalTc (Critical Temperature)Type BaNiF4BiFeO31143Lone pair BiMnO3 Lone PairCs2CdI4Geometric CuO 230 Spin SpyralY-hMnO31270Geometric HoMn2O5 39K2SeO4Geometric LuFe2O4 Charge OrderMnWO413.5Spin Spyral Ni3V2O8 6.5PbVo3Lone Pair TbMnO3 2.7 Spin SpyralZnCr2Se4Recent research works on Multiferroic Ceramics Materials: J. Anthoniappen et al. 6 prepared Samarium (5%Sm) and manganese (0.5%Mn) co-doped BiFeO3 (B5SF0.5MO) polycrystalline multiferroic ceramics by using solid state reaction. they studied the morphology, local polarization switching and piezoresponse, using atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) of the material. X-ray diffraction (XRD) and micro-Raman spectra expose that samarium and manganese co-doping maintains the parental rhombohedral R3c structure of BiFeO3 (BFO). The Saturated localized in-field hysteresis phase and amplitude loops from 180° domains propose the presence of well-defined polarization along the field direction and suggests that Sm and Mn co-doped BFO can be a future material for nanoscale piezoelectric applications. La-modified Bi1?xLaxFeO3 (x = 0.15–0.40) and BaTiO3-modified (Bi1?yBay)(Fe1?yTiy)O3 (y = 0.10?0.33) multiferroic ceramics were prepared via solid-state reactions by Weiren Xia et al. 7. They did XRD and observed strucutural and vibrational properties.Prakash et. al. 8 substituted Zirconium and synthesized Zr substituted Bi0.9Dy0.1Fe1?xZrxO3 (x=0.03, 0.06 and 0.10) multiferroic ceramics by rapid liquid phase sintering technique for improving its multiferroic properties. The distortion in FeO6 octahedra due to Zr substitution hints to splitting of electronic bands of 3.2 eV into multiplets, which in turn reduced the optical band gap value in the range of 2.06–2.10 eV for all samples.Y. Gu et al 9 prepared Sm and Ti co-doped BiFeO3 (BFO) ceramics. with Fe vacancies—Bi0.86Sm0.14FeO3, Bi0.86Sm0.14Fe0.99Ti0.01O3, and Bi0.86Sm0.14Fe0.9Ti0.05O3 by a solid-state method using a rapid liquid process and studied XRD and Raman Spectra. Both the ferroelectric and magnetic properties were shown to correlate with the composition-driven structural evolution. S. R. Mohapatra 10 found Evidence of Magnetoelectric coupling in Bi2(1-x)Ho2xFe4O9(x=0, 0.01) multiferroic ceramics. They studied the strucutral, magnetic,dielectric and magnetoelctric properties of the synthesized compound. D.R. Ratkovski et. al 11. producedBi0.99Y0.01Fe1?xNixO3 ceramics with 0.01?x?0.05 by using a modified solid state reaction method. The low-T magnetic properties were investigated. The ferromagnetism was found more likely to be due small amounts of magnetite. B.Dhanalakshmi et. al. 12.observed Enhanced magnetic and magnetoelectric properties of Mn doped multiferroic ceramics.After their observations they concluded that the Mn doping in single phase/composite BiFeO3 based multiferroic ceramics is capable of enhancing both the ferroelectric and ferromagnetic properties and thereby the magnetoelectric (M-E) coupling as evident from the obtained M-E curves. Quian Zou et. al 13. Dielectric and magnetic properties of Zr substituted YMn0.8Fe0.2O3 ceramics were investigated .They found a promising YMnO3 based multiferroic ceramics with reduced room-temperature dielectric loss. Bhuiyan, M.K.H 14 studied Correlations of Structural, Dielectric, Magnetic and Magnetoelectric Properties of Ca1?xSrx(Fe0.5Ta0.5)O3 Multiferroic Ceramics. Various Ca1?xSrx(Fe0.5Ta0.5)O3 ceramics were synthesized by the standard solid state reaction method. The X-ray diffraction result indicates that all samples are of single phase cubic perovskite structure. The theoretical density (?th) and the bulk density (?B) increase with increasing Sr content. The values of ?th are found to be higher than those of ?B. The value of average grain size was found to be changed with the increase of Sr content. The value of dielectric constant (? ?) for all the compositions was found to be high at lower frequencies, but it increased with the increase in frequency. However, dielectric loss is found to have higher values at lower and higher frequencies for all the compositions. The complex impedance spectroscopy is used to distinguish between the grain and grain boundary contribution to the total resistance. Asymmetric semicircular arcs observed in the Cole-Cole plots indicate that non Debye-type of relaxation exists in the present samples. The Rg is extremely low as compared to Rgb which indicates the conducting nature of the grain. Both the ac conductivity and modulus study reveal hopping type of conduction in the present samples. The real part of initial permeability ( ) ?i ? increases with Sr content up to x = 0.2 and then decreases with increasing Sr content. The maximum values of saturation and remnant magnetization were found to be 1.431 emu/g and 0.461 emu/g. The highest value of ?ME is found to be 58.93 mV/cm?1 Oe?1 . The ME results imply that the composition of Ca1?xSrx(Fe0.5Ta0.5)O3 may have potential applications as multiferroic materials in the future and it may be helpful for better understanding the intrinsic ME coupling and searching high-performance multiferroic ceramics and can potentially be used for fabrication of multifunctional devices such as ME transducers, actuators, sensors and heterogeneous read/write devices.S.N.Kallaev 15.10x experimentd Thermal properties of multiferroic Bi1?xEuxFeO3 (? = 0–0.40) ceramics. Modifying by admixture of Eu was found to change the thermal anomalies of TN. The excess heat capacity is shown being related to Schottky effect. The mechanisms dominating thermal transfer of phonons at TN and TC are determined.Concluding Remarks:Multiferroic ceramic materials show a promising characteristic to tailor the upcoming micro electric devices and other important aspects. This type of ceramic materials synthesis and production technique should be developed and economic to get the essence of material science and engineering’s importance to the whole world.References1J. F. S. ,. R. Orlando Auciello, “The Physics of Ferroelectric Memories,” Physics Today, vol. 51, no. 7, p. 22, 1998.2S. C. a. R. R. Nicola A. Spaldin, “Multiferroics: Past, present, and future,” physics Today, vol. 63, no. 10, p. 38, 2010.3D. Khomskii, “Trend: Classifying multiferroics: Mechanisms and effects,” Physics, vol. 20, no. 2, 2009.4C.-W. Nan, “Multiferroic magnetoelectric composites: Historical perspective, status, and future directions,” Journal of Applied Physics, vol. 103, no. 03, 2008.5M. B. S. F. K. B. J. F. A. B. a. A. F. 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