NanostructuredMultiferroics
Editedby RaneeshBalakrishnan
P.M.Visakh
Editors
Dr.RaneeshBalakrishnan DepartmentofPhysics CatholicateCollege Pathanamthitta Kerala689645 India
Dr.P.M.Visakh
TUSURUniversity DepartmentofPhysicalElectronics 634050Tomsk Russia
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Contents
Preface xi
Editors’Bio xiii
1NanostructuredMultiferroics:CurrentTrendsandFuture Prospects 1
P.M.VisakhandB.Raneesh
1.1Single-phaseMultiferroics 1
1.2MultiferroicStudyofPureBiFeO3 SynthesizedUsingVarious ComplexingAgentsbySol–GelMethod 2
1.3NanostructuredMultiferroics 3
1.4MultiferroicSystemsofBiFeO3 andBaTiO3 Nanostructures:NewIdeas andInsightsfromRecentMagnetoelectricAdvancements 5
1.5EffectivePropertiesofMultilayeredNanomultiferroics 6
1.6CorrelationbetweenGrainSize,Transport,andMultiferroicProperties ofBa-dopedBiFeO3 Nanoparticles 7
1.7SpecificHeatandMagnetocaloricPropertiesofSomeManganite-Based MultiferroicsforCryoCoolingApplications 8
1.8Preparations,Characterization,andApplicationsofMultiferroic Nanocomposites 10
1.9Conclusions 11 References 11
2Single-PhaseMultiferroics 23
PiotrGraczykandEmersonCoy
2.1Introduction 23
2.1.1ConsiderationsonSingle-phaseMultiferroics 26
2.1.2FerroelasticMultiferroics 29
2.2AnalysisoftheMultiferroicityintheHexagonalManganites 30
2.2.1FerromagnetisminHexagonalManganites 30
2.2.2FerroelectricityinHexagonalManganites 32
2.3InvestigationofChargeStatesandMultiferroicityinDopedSystems 32
2.3.1SensitiveOrdering-dopedPerovskiteManganites 32
2.3.2FrustratedLuFe2 O4 –MultiferroisminControversy 35
2.3.3FromtheDzyaloshinskii–MoriyaInteractiontotheExchange Striction 37
2.4MultiferroicPhasesofLone-pairFerroelectrics:Bismuth-Based Compounds 38
2.5StudiesonProperGeometricFerroelectrics 41
2.6Conclusions 44 Acknowledgments 44 References 45
3MultiferroicStudyofPureBiFeO3 SynthesizedUsingVarious ComplexingAgentsbySol–GelMethod 51 VivekVerma,NeelamSingh,andJarnailSinghBangruwa
3.1Introduction 51
3.2Experimental 52
3.3ResultsandDiscussion 53
3.3.1StructuralAnalysis 53
3.3.2MorphologicalAnalysis 54
3.3.3FTIRAnalysis 55
3.3.4MagneticAnalysis 57
3.3.5FerroelectricAnalysis 58
3.3.6DielectricAnalysis 59
3.3.7LeakageCurrentAnalysis 60
3.4Conclusions 61 References 62
4NanostructuredMultiferroics 63 HengWuandXinhuaZhu
4.1Introduction 63
4.2MultiferroicNanoparticles 64
4.2.1Solid-stateReactions 65
4.2.2Molten-saltSynthesis(MSS) 66
4.2.3MechanochemicalSynthesis 66
4.2.4WetChemicalMethods 68
4.2.4.1Sol–GelProcess 68
4.2.4.2Hydrothermal/SolvothermalProcess 69
4.2.4.3Microwave–Hydrothermal(M–H)Process 70
4.3Nanocomposites 73
4.4Core–ShellNanostructures 75
4.5NanostructuresandThinFilmsforMultifunctionalApplications: Technology,Properties,andDevices 77
4.5.1FabricationTechnologies 78
4.5.2PhysicalProperties 79
4.5.2.1FerroelectricProperties 79
4.5.2.2MagneticProperties 81
4.5.2.3PhotocatalyticProperties 82
4.5.3MultiferroicDevices 82
4.6ThinFilmsforPhotovoltaicApplications 84
4.7Conclusions 87 Acknowledgments 88 References 88
5MultiferroicSystemsofBiFeO3 andBaTiO3 Nanostructures: NewIdeasandInsightsfromRecentMagnetoelectric Advancements 95
K.C.Verma,R.K.Kotnala,andNavdeepGoyal
5.1IntroductiontoMultiferroics 95
5.1.1MultiferroicApproachesTowardMagnetoelectricMemories 96
5.1.2MultiferroicPerovskites 97
5.1.3MultiferroicSystemsofBaTiO3 andBiFeO3 Nanostructures 99
5.1.3.1BaTiO3 99
5.1.3.2BiFeO3 100
5.1.3.3LonePairsandChargeOrderingofFerroelectricActivity 101
5.2CrystallineStructureandPhaseTransition 102
5.2.1X-rayDiffraction(XRD)ofBaTM0.01 Ti0.99 O3 [TM = Cr,Mn,Fe,Co,Ni, Cu(1mol%Each)]Nanoparticles 102
5.2.2CrystallineStructureofBiFeO3 NanostructureswithPbDoping 103
5.2.3NanostructuralApproachTowardMultiferroics 105
5.2.3.1NanostructuralInfluenceonFerroelectricPolarization 106
5.2.3.2Nanosize-dependentPhaseStructure 106
5.2.3.3LatticeDefects-relatedNanostructures 107
5.2.4MagneticOrdering 108
5.2.4.1TMIon-substitutedBaTiO3 108
5.2.4.2MagneticOrderinginBiFeO3 110
5.2.5MultiferroicityandMagnetoelectricCoupling:HowtoEnhance 112
5.2.5.1MultiferroicComposites 112
5.2.5.2MultiferroicThinFilmsandNanostructures 116
5.3SynthesisMethodsofBaTiO3 andBiFeO3 Multiferroics 122
5.3.1Sol–Gel:Synthesis 122
5.3.2ChemicalCombustion 123
5.3.3Liquid-phaseDepositionRoute 123
5.3.4HydrothermalSynthesis 123
5.3.5Metallo-organicDecompositionMethod(MOD)forThin-Film Preparation 123
5.3.6ModifiedPechiniMethod 124
5.4Conclusions 124 Acknowledgments 124 References 125
6EffectivePropertiesofMultilayeredNanomultiferroics 133 IvanA.StarkovandAlexanderS.Starkov
6.1Introduction 133
6.2MatrixHomogenizationMethod 134
6.2.1JustificationoftheMatrixHomogenizationMethod 135
6.3LaminateNanocomposites 138
6.4FiberNanocomposites 144
6.4.1BasicEquations 144
6.4.2Anti-planeElasticity 147
6.4.3Axial-symmetryCase 149
6.4.4Maxwell–GarnettTheory 152
6.5Core–ShellNanostructures 153
6.5.1BasicEquations 154
6.5.2HomogenizationProcedurefortheLayeredHollowSphere 156
6.6SummaryandConclusions 159 Acknowledgments 159 References 160
7CorrelationBetweenGrainSize,Transport,andMultiferroic PropertiesofBa-dopedBiFeO3 Nanoparticles 163 M.M.El-DesokyandM.S.Ayoub
7.1Introduction 163
7.2CharacterizationofBa-dopedBiFeO3 MultiferroicNanoparticles 165
7.2.1X-rayDiffraction(XRD) 165
7.2.2ScanningElectronMicroscope(SEM) 167
7.2.3TransmissionElectronMicroscope(TEM) 167
7.2.4FourierTransformInfrared(FTIR)Spectra 169
7.3TransportPropertiesofBa-dopedBiFeO3 Multiferroic Nanoparticles 170
7.3.1NatureofConductionMechanism 172
7.3.2RelationBetweenActivationEnergyandMeanDistanceBetweenIron Ions 174
7.3.3NatureofSmallPolaron-hopping(SPH)Conduction 176
7.3.4SmallPolaron-hopping(SPH)Parameters 176
7.3.5HoppingCarrierMobilityandDensity 177
7.4MultiferroicPropertiesofBa-dopedBiFeO3 Multiferroic Nanoparticles 178
7.4.1FerromagneticProperties 178
7.4.1.1MolarMagneticSusceptibility(λM ) 178
7.4.1.2NéelTemperature(TN ) 180
7.4.2FerromagneticHysteresisLoop 180
7.4.3FerroelectricProperties 184
7.4.3.1TemperatureDependence 184
7.4.3.2FrequencyDependence 187
7.4.4FerroelectricHysteresisLoop 188
7.5Conclusion 189 References 190
8SpecificHeatandMagnetocaloricPropertiesofSome Manganite-BasedMultiferroicsforCryoCooling Applications 193 N.PavanKumar,ElleSagar,andP.VenugopalReddy
8.1Introduction 193
8.1.1MagneticRefrigeration 193
8.1.2MagnetocaloricEffect 194
8.1.3MagnetocaloricEffectandMagneticTransition 195
8.1.4ManganitesasMagnetocaloricMaterials 195
8.1.5MagnetocaloricEffectinRareEarth-BasedMultiferroic Manganites 196
8.1.6MethodsfortheDeterminationofMagnetocaloricEffect 196
8.1.6.1DirectMeasurements 196
8.1.6.2IndirectMeasurements 197
8.1.7PropertiesofanIdealMagneticRefrigeratorMaterial 198
8.2MultiferroicMaterialsandTheirStructure 198
8.2.1RareEarth-BasedMultiferroicManganitesBasedonTheir Structures 198
8.2.1.1HexagonalManganiteMultiferroics 199
8.2.1.2OrthorhombicManganiteMultiferroics 199
8.3SpecificHeatandEstimationofMagneticEntropy 200
8.3.1SpecificHeat 200
8.3.1.1RMnO3 (R = Sm,Eu,Gd,Tb,andDy) 200
8.3.1.2Tb1 x Dyx MnO3 (x = 0,0.1,0.2,0.3,and0.4) 204
8.3.1.3RMn2 O5 (R = Tb,Dy,andHo) 205
8.3.2EstimationofMagneticEntropy 208
8.3.2.1RMnO3 (R = Sm,Eu,Gd,Tb,andDy) 208
8.3.2.2Tb1 x Dyx MnO3 (x = 0,0.1,0.2,0.3,and0.4) 211
8.3.2.3RMn2 O5 (R = Tb,Dy,andHo) 211
8.4MagnetocaloricProperties 213
8.4.1RMnO3 Series 214
8.4.1.1OrthorhombicNdMnO3 ,SmMnO3 ,andEuMnO3 214
8.4.1.2OrthorhombicGdMnO3 ,TbMnO3 ,andDyMnO3 216
8.4.1.3HexagonalDyMnO3 220
8.4.1.4HexagonalHoMnO3 220
8.4.2Group2Series(DopedRare-earthManganites) 221
8.4.2.1OrthorhombicDy-dopedTbMnO3 221
8.4.2.2h-YbMnO3 DopedwithTransitionMetalsandRareEarths 223
8.4.3RMn2 O5 (R = Tb,Dy,andHo)Series 224
8.5Conclusions 227
References 228
x Contents
9Preparations,Characterization,andApplicationsof MultiferroicNanocomposites 233
P.M.Visakh
9.1Introduction 233
9.2PreparationofMultiferroicNanocomposites 235
9.3CharacterizationsofMultiferroicNanocomposites 238
9.4ApplicationsofMultiferroicNanocomposites 240
9.5Conclusions 241
References 241
Index 249
Preface
Thebook NanostructuredMultiferroics: summarizesmanyoftherecentresearch accomplishmentsintheareaofmultiferroics.Wediscussmanytopicssuchas nanostructuredmultiferroicscurrenttrends,newchallengesandopportunities, structureandproperties’relationshipinmultiferroicsystems.Thebookgives acomprehensiveaccountofsingle-phasemultiferroics,multiferroicstudyof pureBiFeO3 synthesizedusingvariouscomplexingagentsbysol–gelmethod, nanostructuredmultiferroics,multiferroicsystemsofBiFeO3 andBaTiO3 nanostructures.Newideasandinsightsfromrecentmagnetoelectricadvancements; effectivepropertiesofmultilayerednanomultiferroics;correlationbetweengrain size,transport,andmultiferroicpropertiesofBa-dopedBiFeO3 nanoparticles; specificheatandmagnetocaloricpropertiesofsomemanganite-basedmultiferroics forcryocoolingapplications;preparations,characterization,andapplicationsof multiferroicnanocompositesarealsoincludedinthisbook.
Thisbookwillbeaveryvaluablereferencesourceforuniversityandcollege faculties,professionals,researchfellows,seniorgraduatestudents,researchers inR&Dlaboratoriesworkingintheareaofnanostructuredmultiferroics.The variouschaptershavebeencontributedbyprominentresearchersfromindustry, academia,andgovernment/privateresearchlaboratoriesacrosstheglobe.Itcovers anup-to-daterecordonthemajorfindingsandobservationsinthefieldofmultiferroicnanocomposites.Thefirstchapterdiscussesabout,scope,stateofart,current trendsnewchallenges,andopportunitiesofmultiferroicnanosystems.
Secondchaptertitled“Single-phaseMultiferroics”givesabetterreviewon structure-propertyrelationships.Theauthorsdiscussmanytopicssuchasimportanceofsingle-phasemultiferroics,ferroelasticmultiferroics,analysisofthe multiferroicityinthehexagonalmanganites,ferromagnetisminhexagonalmanganites,ferroelectricityinhexagonalmanganites,investigationofchargestates andmultiferroicityindopedsystems,frustratedLuFe2 O4 ,multiferroicphasesof lone-pairferroelectrics,andstudiesonpropergeometricferroelectrics.Chapter3 dealswithmultiferroicstudyofpureBiFeO3 synthesizedusingvariouscomplexing agentsbysol–gelmethod.Inthischapter,theauthorsdiscussexperimentalmethod, structuralanalysis,morphologicalanalysis,FTIRanalysis,magneticanalysis, ferroelectricanalysis,dielectricanalysis,andleakagecurrentanalysisofBiFeO3 multiferroics.
Thefourthchapteristitled“NanostructuredMultiferroics.”Followinganintroductiontothemultiferroicnanoparticles,thechaptergoesontodiscussdifferent synthesismethod,coreshellnanostructuresandmultifunctionalapplicationsof nanostructuresthinfilms.Thefifthchapter“MultiferroicSystemsofBiFeO3 and BaTiO3 Nanostructures:NewIdeasandInsightsfromRecentMagnetoelectric Advancements”.Inwhichthemultiferroicapproachtowardmagnetoelectricmemories,multiferroicsbasedonBaTiO3 andBiFeO3 nanostructures,multiferroicity andmagnetoelectriccoupling,andsynthesismethodsforBaTiO3 andBiFeO3 multiferroicsarecriticalityanalyzed.
Thesixthchaptertheauthorsexplaintheeffectivepropertiesofmultilayered nanomultiferroicsthroughmatrixhomogenizationmethod,justificationofthe matrixhomogenizationmethod,laminatenanocomposites,fibernanocomposites, basicequations,anti-planeelasticity,axial-symmetrycase,Maxwell–Garnetttheory, core–shellnanostructures,andhomogenizationprocedureforthelayeredhollow sphere.
Theseventhchapterofthisbookistitled“CorrelationBetweenGrainSize, Transport,andMultiferroicPropertiesofBa-dopedBiFeO3 Nanoparticles”.In thischapter,theauthorsdiscussmaintopicssuchas,transportproperties,and multiferroicpropertiesofBa-dopedBiFeO3 multiferroicnanoparticles.Specific HeatandMagnetocaloricPropertiesofSomeManganite-basedMultiferroicsare discussedinchaptereight.
Thefinalchapterpresentsanoverviewof–preparationofmultiferroicnanocomposites,characterizationsofmultiferroicnanocomposites,andapplicationsofmultiferroicnanocomposites.
Finally,wewouldliketoexpressoursinceregratitudetoallthecontributorsofthis book,whogaveexcellentsupporttothesuccessfulcompletionofthisventure.We aregratefultothemforthecommitmentandthesinceritytheyhaveshowntoward theircontributioninthebook.Withouttheirenthusiasmandsupport,compilation ofthisbookwouldhavenotbeenpossible.Wewouldliketothankallthereviewers whohavegiventheirvaluabletimetomakecriticalcommentsoneachchapter.We alsothankthepublisherWiley-VCHforrecognizingthedemandforsuchabook, forrealizingtheincreasingimportanceoftheareaofnanostructuredmultiferroics, andtheircurrenttrendsandfutureprospects.
B.Raneesh
P.M.Visakh
Editors’Bio
Dr.B.Raneesh isanAssistantProfessorintheDepartmentofPhysics,CatholicateCollege,Pathanamthitta,Kerala,India.HereceivedPh.D.inPhysicsfromMahatma GandhiUniversity,Kerala,India.Hiscurrentresearchinterestsincludemultiferroics,thinfilms,nanocomposites,and electronmicroscopy.Hehaspublishedmorethantwenty researcharticlesinpeer-reviewedinternationaljournals. Healsoco-editedthreebooksandco-authoredfourbook chapters.Source:Dr.B.Raneesh.
Dr.VisakhP.M.(MSc,MPhil,PhD) isaprolificeditor withmorethan 30publishedbooks.HeisworkingasassistantprofessorinTUSURUniversity,Tomsk,Russia,since 2017.HedidhispostdocresearchinTomskPolytechnicUniversity,Tomsk,Russia(2014–2017).HeobtainedhisPhD, MPhil,andMScdegreesfromSchoolofChemicalSciences, MahatmaGandhiUniversity,Kottayam,Kerala,India.He hasedited 30books ofScrivener(Wiley),Springer,Royal SocietyofChemistry,Elsevier,andmorethan 10books in press(Wiley,Springer,RoyalSocietyofChemistry,andElsevier).Hehasbeeninvited asavisitingresearchertoRussia(2014topresent),Portugal(2013,2014),Czech Republic(2012,2013),Italy(2009,2012),Argentina(2010),Sweden(2010,2011, 2012),Switzerland(2010),Spain(2011,2012),Slovenia(2011),France(2011),Belgium(2012),andAustria(2012)forhisresearchwork.Hehasvisited12countries, and15universitiesinEurope.Hehas20publications,4reviews,andmorethan30 bookchapterstohiscredit.Hehasattendedandpresentedatmorethan28conferences,has1339 citations, andhis h-indexis17.Heactsasguesteditorfor4 internationaljournals.Source:Dr.VisakhP.M.
NanostructuredMultiferroics:CurrentTrendsandFuture
Prospects
P.M.Visakh 1 andB.Raneesh 2
1 DepartmentofPhysicalElectronics,TUSURUniversity,Tomsk,Russia
2 DepartmentofPhysics,CatholicateCollege,Pathanamthitta,Kerala,India
1.1Single-phaseMultiferroics
Inferroics,atleasttwometastablestatescanbefound.Thesestatesarerelatedto thedirectionalarrangementandcrystallinelimitationsofthematerials,providing reversible“storedstates”thatcanbeswitchedbyexternalfields.Forexample,in ferromagnets,anexternalmagneticfieldcanflipthedirectionofthematerialmagnetizationtoalignparalleltothefielddirection.Thisphenomenonhasfoundseveral applicationsnowadays,especiallyinelectronicsandinformationstoragedevices, bothforferroelectricandferromagneticmaterials[1].Multiferroicsarespecialclass ofmaterialswhichpossessmorethanoneoftheprimaryferroicpropertiesinthe samephase.Multiferroicmaterialsareofgreatinterestintheelectronicsindustry forapplicationasmemorystoragedevices[2,3],spintronics[4],components[5], andsensors[6].Theperovskitestructureisperhapsthemostcommoncrystalline structureformultiferroicmaterialsstudiedsofar.Itssimplicityisduetoitsrather straightforwardorganizationandchemicalconstitution.ThegeneralperovskiteformulaisABX3 ,whereAandBarecationsandXisananion,typicallyoxygen,but alsoothers,likefluorine,aresometimesconsidered.Materialsinwhichmultiple ferroicorderingtakeplacehadbeenalreadystudied,asearlyas1960s.Thoseearly studiesfocusedonthesynthesisofcompoundswithextremelycomplexstoichiometry,suchas(1 x )PbFe0.66 W0.33O3 – x PbMg0.5 W0.5 O3 [7]andnickeliodineboracite, (Ni3 B2 O13 I)[8],bothofwhichpresenttoolargeionicinteractionsandcrystallinedistortionstobeabletodeterminethetrueoriginoftheirmultiferroicbehavior.Nevertheless,themethodologywasconceptuallysimple:itaimedtoreplaced0 Bcations,in ferroelectricperovskiteoxides,bymagneticdn cations[9].Tounderstandmagnetic interactionsinperovskites,itisimportanttodiscusstheGoodenough–Kanamori rule.ItwasfirstformulatedbyGoodenoughin1955,andmorerigorousmathematicalunderpinningwassubsequentlyprovidedbyKanamori(1959).Itisappliedto interatomicspin–spininteractionsbetweentwoatomsthataremediatedbyvirtual electrontransfers,forexampleintheNi2 + –O–Mn4+ chain[10,11].
NanostructuredMultiferroics, FirstEdition.EditedbyRaneeshBalakrishnanandP.M.Visakh. ©2021WILEY-VCHGmbH.Published2021byWILEY-VCHGmbH.
1NanostructuredMultiferroics:CurrentTrendsandFutureProspects
Ferroelectricityandferromagnetismseemedatthebeginningtobemutually exclusiveinmostcases;muchefforthasgonetoovercomethisproblemthesearch forsingle-phasematerials,whichcanallocatetwoormoreferroicorders,isstill ofhighscientificinterest.Onewaytoachievethisgoalistoadopttheso-called lonepairsofbigstereochemicalactiveatomssuchasBi3+ orPb2+ [12–15].Magneticandelectricferroicstatesaremostlyindependentofeachother.Findinga materialinwhichtheelectricfieldcanaffectnotonlythepolarizationbutalso themagnetization(E[P,M ] )and,inequalmanner,amaterialinwhichthemagnetic fieldalsoaffectsmagnetizationandpolarization(H [M,P] ),arehighlydesirable intheindustry.Severalstudieshaveshownferroelasticswitchinginthinfilms [16–18]toexhibitthepotentialapplicabilityofthesematerialsinmultifunctional heterostructures[19,20]orartificialmultiferroicarchitectures[21].Moreover,in materialssuchasBiFeO3 ,PbTiO3 ,andBaTiO3 ,theferroelasticdomainsareknown toplayanimportantroleinfacilitatingthecouplingbetweenthepolarizationand themagnetizationviatheferroelasticswitching[22,23],anaspectthatishighly desirableinnonvolatilememories[24,25].Additionally,domainwallshavebeen showntohaveaverystrongeffectonheatflowandphononscattering,whichcan dramaticallyaffectdeviceperformance[26].Thecompoundsconsideredabove belongtotheclassoftypeImultiferroics,wherethechargeorderandferroelectricity isof“electric”origin.e.g.HoMnO3 whichhasanE-typemagneticorder[27,28]. IntypeIImultiferroics,themagnetismcausestheferroelectricpolarization,thus, implyingastrongmagnetoelectriccoupling.
Therearetwomechanismsthatgovernchargeorderthroughmagneticorder [29,30].ThefirstistheinverseDzyaloshinskii–Moriyainteraction(DMI).Thiseffect isarelativisticcorrection(spin–orbitinteraction)tothesuperexchangebetween twoTMmagneticionsthroughtheoxygen.IthasbeenobservedinRMn2 O5 compounds,whereitinducesspiralmagneticorder.Thesecondmechanismof magneticallydrivenferroelectricityistheexchangestriction.
1.2MultiferroicStudyofPureBiFeO3 SynthesizedUsing VariousComplexingAgentsbySol–GelMethod
Duetolong-termtechnologicalaspirationsinthisfield,alotofresearchworkhas beenreported.Thesurgeofinterestinmultiferroicmaterialsoverthepast15years hasbeendrivenbytheirfascinatingphysicalpropertiesandhugepotentialfor technologicalapplications.So,therehasbeenthesearchforaparticularmaterialto fulfilltherequirementtobeagoodmultiferroicmaterial.Wangetal.[31]worked toenhancepolarizationandrelatedpropertiesinhetero-epitaxiallyconstrained thinfilmsofthemultiferroicBiFeO3 (BFO).Thefilmdisplaysaroom-temperature spontaneouspolarization(50–60 μC/cm2 ),almostanorderofmagnitudehigher thanthatofthebulk(6.1 μC/cm2 ).TheCurietemperature(T c )andtheNeel temp(T N )ofBFOare1103and673K,respectively,duetowhichitactsasa goodmultiferroicmaterialatRT[14].SubhashSharmaetal.[32]reportedthe comparativestudiesofpurebismuthferritepreparedbysol–gelmethodversus
1.3NanostructuredMultiferroics 3 conventionalsolid-statereactionmethod.Thisgroupfoundthatsol–gelmethodis bettercomparedtosolid-statemethodforpreparingpurephaseofBFOatlowtemperatures.TheprecursorsusedareBi(NO3 )3 ⋅5H2 O,Fe(NO3 )3 ⋅9H2 O,anddistilled water.Differentcomplexingagentslikecitricacid,oxalicacid,glycine,andmalonic acidin1:1Mratioofmetalionswere addedinstoichiometricsolutionofabove precursorswithconstantstirring.ThegrainsofBFOsamplesusingdifferentacids arerectangularandthetypeofstructureisrhombohedral[33].BFOisreportedas G-typeantiferromagneticduetolocalspinorderingofFe3+ atRT.Atthesametime, thereareseveralreportsthatshowferromagnetic-likemagnetichysteresisinpure bismuthferrite.Bismuthferrite,preparedusingcitricacid,maybeagoodcandidate forfurtherstudies.ItcanbeobservedthatBFOpreparedbysol–geltechniqueusing citricacidascomplexingagentshowsgoodferroelectricpropertiesascompared toothermethods,anditexhibitsarhombohedralperovskitestructurewithless impurity[34].
DielectricpropertiesofBFOsamples,preparedbyusingvariouscomplexing agentsandannealedat600 ∘ C,asafunctionoffrequencyhavebeenmeasuredin therangeoffrequency102 –106 Hz.Itcanbeobservedthatthedielectricconstant decreasesonincreasingfrequencyandbecomesindependentathigherfrequencies. Thedecrementin ��’isattributedtothedielectricrelaxation.Thevariationof leakagecurrentforappliedelectricfieldofBFOfordifferentacidsannealedat 600 ∘ C.Thisgivesanideaofleakagecurrentofsamplesforappliedelectricfield. Theleakagecurrentisintherangeof10 5 –10 10 A/cm2 formaximumappliedfield 4000V/cm.InBFO,oxygenvacanciescanbeproducedbythevaporizationofBior thepresenceoflower-valenceFe2+ ions,whichleadtotheformationofatraplevel at0.6eVbelowthebottomedgeoftheconductionband.X-raydiffractionpatterns andFouriertransforminfraredanalysisofvarioussamplesshowthedegreeof formationofrequiredphase.Ferroelectricandmagneticstudyofsamplesprepared at600 ∘ Cshowstheircomparativemultiferroicproperties.Samplesshowgood magneticandferroelectricpropertiesatRT,whicharethefundamentalrequirement foranymultiferroicmaterial.
1.3NanostructuredMultiferroics
Bismuthferrite,BFO,asoneoftheveryfewsingle-phasemultiferroicswithasimultaneouscoexistenceofferroelectric-andantiferromagnetic-orderparametersatRT, hasattractedconsiderableattentionsinceitsdiscoveryin1960.Muchworkhas beencarriedoutonthesynthesisofpureBFOnanoparticlesbynumerousmethods (e.g.solid-statereactions[35–37],wetchemicalsynthesis,includingsol–gelmethod withtheuseofpolymericprecursors[38–40],solutioncombustionmethods[41,42], mechanicalactivation[43],mechanochemicalsynthesis[44–46],hydrothermalprocess[47–49]).Parketal.[50]havealsoreportedanincreasedmagnetizationvalue atthenanoscale,whileMazumderetal.[51]havedemonstratedthatnanoscale BFOdepictsnotonlyhighsaturationmagnetizationbutalsogenuineferromagnetic behaviorwithfinitecoercivityatRT.Recently,multiferroicBFOnanoparticlesand
1NanostructuredMultiferroics:CurrentTrendsandFutureProspects
La-dopedBFOnanoparticleshavebeensynthesizedbyMSSprocessintheNaCl [52,53],NaCl–KCl[54,55],NaCl–Na2 SO4 [56],orKNO3 –NaNO3 [57]moltensalt. Perejonetal.[58]demonstratedthatpureBFOnanoparticlesweresynthesized viathedirectmechanochemicalreactionbygrindingpureFe2 O3 andBi2 O3 inan oxygenatmosphereatreactiontimesevenlessthan50minutes.Crystallitesizeof theBFOnanoparticlesfrom13to20nmcouldbetailoredbycontrollingthemilling conditions,particularlythemillingpower.Sol–gelprocessisapopularprocessing routeforthesynthesisofperovskiteoxidenanoparticles(e.g.BaTiO3 [59],PbTiO3 [60],BiFeO3 [61,62]).Thisprocessinvolvestheformationofasolbydissolving themetaloxides,metal–organic,ormetal-inorganicsaltprecursorsinasuitable solvent,subsequentdryingofthegel,followedbycalcinationandsinteringathigh temperature.
Thehydrothermalmethod,involvesheatinganaqueoussuspensionofinsoluble saltsinanautoclaveatamoderatetemperatureandpressurewherethecrystallizationofadesiredphasetakesplace.Solvothermalsynthesisisalsodefinedasa hydrothermalreactionthatoccursinanonaqueoussolutioninthehydrothermal processofBFOnanoparticles,Bi3+ andFe3+ ionsarefirsttransformedintohydroxide Fe(OH)3 andBi(OH)3 intheprecursor,andthendissolvedintheprecursorwiththe presenceofalkalinemineralizers(e.g.KOH,NaOH,LiOH).Whentheionicconcentrationinthealkalinesolutionsurpassesthesaturationpoint,theBFOphasebegins tonucleateandprecipitatefromthesupersaturatedhydrothermalfluid,followedby crystalgrowth[63,64].
Theterm“microwave-hydrothermalprocess”wascoinedbyKomarnenietal.[65] intheearly1990s,andthisprocesshasbeenusedfortherapidsynthesisofnumerousceramicoxides,hydroxylatedphases,porousmaterials,andhematitepowders [66–68].Itoffersmanydistinctadvantagesoverconventionalhydrothermalsynthesis,suchascostsavingsduetorapidkineticstimeandenergy,rapidinternalheating,andsynthesisofnewmaterials.Themorphologiesofthecomponentphasesin suchverticalcompositefilmscontainingeithermagneticorferroelectricnanopillarsvariedmarkedlywiththesubstrateorientationandphasefractions[69]was inferredfromtheirmicroscopyobservations.Raidongiaetal.[70]reportedacomprehensivestudyoncore–shell(CFO@BTO)nanoparticlesandnanotubes.Core–shell typenanotubesexhibitalargesaturationmagnetizationandremanentmagnetizationascomparedtothenanoparticles,sincethenanotubeprovidesalargeinterfacialareabetweentwophases.TheNiZnFe2 O4 @BTOcore–shellnanostructures werealsoextensivelystudiedbyCurecheriuetal.[71]andTestinoetal.[72].In thepastdecades,therewaswidespreadscientificinterestinmultiferroicnanostructuresandthinfilms,owingtotheirfascinatingmultifunctionalpropertiesdriven byeitherinterface-inducedstrain(typicallyinmultiferroicthinfilms)[73–75]or byanintrinsicsizeeffect(innanostructures),whichprovidesthebasisfordevelopingthenext-generationelectronicdevices.Thetop-downapproachinvolvesthe constructionofsmall-sizedstructuresfromlargeonesthroughetchingandremoval ofparts[76,77].Inthismethod,lithographyusuallyisappliedtoproducenanostructureswithassistancefromenergyparticlessuchasphotons,ions,orelectron beams.Focusedionbeam(FIB)millingandelectronbeamdirectwriting(EBDW)
1.4MultiferroicSystemsofBIFEO3 andBATIO3 Nanostructures 5 arepopulartechniquesforfabricationofnanostructureswithcontrolledsizeand shape.
1.4MultiferroicSystemsofBiFeO3 andBaTiO3 Nanostructures:NewIdeasandInsightsfromRecent MagnetoelectricAdvancements
SinceBaTiO3 couldexistinfourdifferentphasesdependingonthetemperature–the paraelectriccubic,ferroelectrictetragonal,orthorhombic,andrhombohedral phases–theresultingdisplacementgivesapolarizationof26 μC/cm2 alongthe (001)direction[78].Theoriginalcubicsymmetryisdistortedbylengtheningofthe c latticeconstant(c/a = 1.011)[79].TheperovskiteBiFeO3 withhigh T c ∼ 1103K and T N ∼ 643Kattractslotofattentionbecauseithassimultaneousferroelectric andantiferromagneticorderingevenatRT.Thisisbecausetheferroelectricityin BiFeO3 originatesfromthe6s2 lonepairelectronsofBi3+ ionsduetostructural distortion,whilethemagnetismoccursbyFe–O–Fesuperexchangeinteractions. Asanoverview,BiFeO3 hasadisappointinglylowspontaneouspolarizationand saturationmagnetizationduetothesuperimpositionofaspiralspinstructureof antiferromagneticorder[80].Inthisspiralspinstructure,theantiferromagnetic axisrotatesthroughthecrystalwithanincommensuratelongwavelengthperiod of62nm,whichcancelsthemacroscopicmagnetizationandalsoinhibitsMEcoupling.Hence,fornovelelectronicsofBiFeO3 ,itsmagneticandelectricproperties mustbeenhanced.ThesuperexchangebetweentheoctahedrallycoordinatedFe3+ throughtheOligandisresponsiblefortheantiferromagnetism,butBiFeO3 has beenreportedtohaveaweakferromagneticcomponentatRTandisthuscanted, withahelicalrepeatof ∼620Å[81].
Hund’srulecouplingwouldleadtospinsoftheTM3dshellinparallelorientation andthismechanismbreaksthestrongcovalentbondsthatarenecessaryforferroelectricity[82].Forexample,inBiFeO3 andBiMnO3 ,theferroelectricityisduetothe lonepairsofnonmagneticBi,andinYMnO3 ,itisduetotiltingofalmost-rigidMnO5 trigonalbipyramids[83].ThestructureoftheferroelectricBiFeO3 phasehasbeen resolvedexperimentallyusingX-rayandneutrondiffractionandfoundtopossessa highlydistortedperovskitestructurewithrhombohedralsymmetryandspacegroup R3c[84].Itcreatesaneffectivenegativepressurethatledtoavolumeexpansion [85].Theincreaseinc/adistortionleadstohigherdeformationoftheTiO6 octahedra[86].Thetypeofnanomaterialsisnotwelldefinedintheliterature,butit isconsideredthatatleastoneofitsdimensionsisbelow100nm[87].Thedistributionofnanomaterialsisdependentuponitsdimensionality;asystemhavingall threedimensionswellbelow100nm(criticallength)isconsideredasquantumdots onemaindifferencebetweenferroelectricnanostructuresandbulkmaterialsisthe presenceofdepolarizingfieldintheformerbecauseoftheuncompensatedcharges atthenanostructuralsurface[88].Thedepolarizingfieldinnanosystemsisableto quenchspontaneouspolarization[89].Anexternalelectricfieldsandshort-circuit boundaryconditionsareneededtoscreenthedepolarizingfield[90,91].Modified
1NanostructuredMultiferroics:CurrentTrendsandFutureProspects
PechinimethodwasalsousedtoprepareBiFeO3 nanoparticles[92,93].TherhombohedraldistortioninBiFeO3 fromcubicstructureisreducedbydecreasingparticle sizeaccompaniedbydecreasingpolarizationinferredfromatomicdisplacements. Thesize-dependentatomicdisplacementinmultiferroicnanostructurereflectsthe effectofincreasingdepolarizationfieldwithdecreasingcrystallitesize[94].
Insmall-sizednanostructures,thesurface-to-volumeratiobecomessolargethat itincreasesagainwithdecreasingparticlesize.Caoetal.[95]reportedaCo-doped BaTiO3 systemforwhichtheCo-3dstates,rangingfrom 6eVtoFermilevel,have astronghybridizationwithO-2pstates.Itinvolvesdouble-exchangemechanism offerromagnetism.Thebondingofthechargecarriersmediatestheexchange interactionviaoxygenvacancywithinthelocalspinstocontributeferromagnetism. SuperimpositionofZFC/FCplotsaround300Kandaclearseparationbetween FC/ZFCatlowtemperature,withoutblockingtemperature,indicatethattheTM ionsinBaTiO3 arenotstronglyantiferromagnetic[96].Itwaspredictedthatthe hybridizationbetweentheTM3dorbitalsandtheO2pistheoriginofobserved magnetism[97].Thesevaluesofpolarizationaremuchlargerthanthoseobserved inpureBiFeO3 becauseoftheformationofBi2 Fe4 O9 phase,whichcauseslower electricalresistivity[98,99].ThedopingofBaTiO3 islocatedatFesiteandacts asacceptorforimprovingtheelectricalpropertiesofBF–BTnanoparticles.For this,thedopedBaTiO3 actsasanacceptortoeffectivelycompensatethecharge carrierstoFe2+ ionsattheFesiteandinduceloweroxygenvacancy.Tomodify propertiesthroughsizequantizationsuchasthesuppressionofthespinspiral inBiFeO3 andstabilizingphasesthatareinaccessiblethroughconventionalbulk techniques,thin-filmgrowthtechniquesprovidetheabilitytovarythelattice mismatchbetweenthefilmandthesubstrate,soastointroduceepitaxialstrainin thethin-filmmaterial.
1.5EffectivePropertiesofMultilayered Nanomultiferroics
Theuseofmultiferroicmaterialsisbasedonthemagnetoelectric(ME)effect.This effectconsistsintheappearanceofanelectricfieldundertheactionofanexternalmagneticfieldandviceversa.InthenaturalmultiferroicCr2 O3 ,themaximum MEcoefficientisobservedatatemperatureof260Kandamountsto3.7pS/m[100]. Unfortunately,thisvalueisinsufficientforpracticalcommercialapplications.ME coefficientsgreaterbyabouttwoordersofmagnitudeweredemonstratedforTbPO4 [101]andHO2 BaNiO5 [102].Thematrixhomogenizationmethod(MHM)presented inthisunitprovideseffectiveparametersofalayeredstructurewithoutsolution ofdifferentialequationsinpartialderivatives[103–107].Tocalculatetheparameters,onlyoperationswiththematricesenteringintotheequationsareinvolved.The methodcanbeeasilygeneralizedforboundaryconditionsdifferentfrom[110].The effectivemediumwouldpossessthesameanisotropyformonoclinic,orthorhombic,tetragonal,andtrigonalsystems[111].Theeffectivestructurewithinitialcubic anisotropyistetragonal,asacubicmediumisaparticularcaseofthetetragonalone.
1.6CorrelationbetweenGrainSize,Transport,andMultiferroicProperties 7
Fibercompositesarethemostcommonnanostructuresandareinuseinavariety ofsystems[112].Typically,theyaremodeledbyasetofcylinders(inclusions), whicharecoatedwithmultiplelayersofdifferentmaterialsandimmersedina matrixofanothermaterial.Thepresenceofanadditionalparameter–thecurvature ofthecylindricallayer–giveshopetostrengthentheinteractionbetweenthe electric,magnetic,andelasticfields.Thatis,byusingfibergeometry,onemay beabletodesignnanocompositemultiferroicswithlargerME,piezoelectric, and/orpiezomagneticcoefficients.Core–shellnanocompositeshavebeenan activeresearchareainthepastyearsbecauseoftheirpromisingmultifunctional capabilities.Thesestructuresdemonstratenovelcharacteristicsthataredifferent fromtheirsingle-componentcounterpart.Someapplicationscanalreadybefound inbioimaging,cloaking,drug/genedelivery,nanophotonics,optics,andsensors [113–121].Multilayernanoshells,orso-callednanomatryoshkas,areaparticular andverypromisingcaseofcore–shellnanomaterials.Theclassicalelectromagnetic theoryissufficienttoestimatetheopticalparametersofnanomatryoshkaswith core–shellseparationslargerthanananometer.Unfortunately,duetothebypass ofelectrontransportbetweenthecoreandshellthroughtheself-assembledmonolayer[122],classicalapproachfailsforthedescriptionofnanomatryoshkaswith subnanometer-sizedgaps.Thus,thereisneedtoemployaquantumapproachfor themodelingofthesmall-sizednanomatryoshkas(lessthan1nm).Comparedto earlierpublishedworks[123–125],thisapproachdoesnotrequireusageofspecial functionslike,e.g.sphericalorBesselfunctions.
Thecomputationalschemeismuchsimplerthanthepreviouslyexistingone,even fortheelectrostaticproblem.Itallowsfindingsolutionsofmorecomplexproblems accountingfortheinteractionofthefieldsofdifferentnature[126].Forthedeterminationofthematerialcoefficientsofthiseffectivemediuminthecaseofsmalltotal thickness,itisrecommendedtousetheMHM,whichdoesnotrequirethesolution ofacomplexsystemofmagneto-electro-elasticityequations.Thedesiredeffective characteristicsareobtainedusingonlyoperationswithmatricescharacterizingthe propertiesofsinglenanolayers.Thisfactsignificantlysimplifiesthecalculationsand allowsmultilayernanosystemstobeaccuratelyandeasilydescribed.
1.6CorrelationbetweenGrainSize,Transport,and MultiferroicPropertiesofBa-dopedBiFeO3 Nanoparticles
BiFeO3 isoneofthesingle-phasemultiferroicmaterialswithadistortedperovskite structureABO3 [127],whichshowsmultiferroicbehavioratRThavinghigh ferroelectricCurietemperature(T C ∼ 1100K)andantiferromagneticNéeltemperature(T N ∼ 640K)[128],anditcontinuestobetheonlycompoundwithcoexistence offerroelectricityandantiferromagnetismatRT[129].Theferroelectricityand magnetisminBiFeO3 isattributedtotheBi3+ 6s2 lonepairelectronsandpartially filleddorbitalofFe3+ ion,respectively[130];thus,thecouplingbetweenthe ferroelectricandmagneticorderingisusuallyconsideredtoberatherweak[131]. Theimpurities,largeleakagecurrent,andantiferromagneticnaturearebighurdles
1NanostructuredMultiferroics:CurrentTrendsandFutureProspects
inBiFeO3 applications[132],anditisverydifficulttoobtainasingle-phaseBiFeO3 byusingsolid-statereactionathighsinteringtemperature[51].DopingatA-site affectsthecentrosymmetryofFeO6 octahedra,createsoxygenvacancies,andleads tochangeinmultiferroicpropertiesofBiFeO3 .Furthermore,theleakagecurrents arereducedbyBa2+ iondoping[133,134].Leakagecurrentduetooxygenvacancies orimpuritiesisthemajorprobleminBiFeO3 .Ithasbeenobservedthatdoping atA-sitesreducestheleakagecurrentinBiFeO3 andenhancesthemultiferroic properties[135].
ThesubstitutionofBi3+ byBa2+ maycausetwoparallelphenomenawithrespect totheconcentrationofoxygenvacancies:(i)thecreationofoxygenvacanciestoneutralizethechargeproducedsubstitutingBi3+ byBa2+ ,(ii)decreaseinconcentration ofoxygenvacanciesbyfillingtheprobablevacantvolatilizedBi3+ sites[136].The spectraof630cm 1 areofstrongmetaloxygen-bendingvibrationofM–O4 [137,138]; suchbandvibrationisapossibilityinimpurityphase,sinceminorimpurityphase wasseenonsubstitutioninXRD.ThemagneticpropertiesofBiBaFeO3 multiferroicnanoparticlesdependonparticlesizebecauseoflong-rangespinarrangement. Thereductioninparticlesizebelowtheperiodicityofcycloidalspinstructurewill enhancethemagneticproperties.However,theweakferromagneticfoundingin BiBaFeO3 multiferroicnanoparticlesoriginatedfromcantingintheFe3+ moments duetotiltof<FeO6 >octahedronandthedistortioncansuppressthespiralspin structureandincreasetheweakferromagnetism.Duetothesmallparticlesize, theelectronspinsfluctuate;thisresultsindecreasingNéeltemperatureasthefluctuationscreatedisorder.Inaddition,thereasonmayberelatedtothedecreaseof magneticexchangeinteractionswithreductioninparticlesize[92].
ThesubstitutionofdivalentmetalionsBa2+ attrivalentBi3+ sitesrequiresoxygen deficiencyforcompensatingcharge,andthismaydestabilizethesystem[139].It isexpectedtosuppressthecycloidspinstructure[140].Thesmallparticlesizes observedinthesamplesoftheorderof30nmareexcellentforefficientferromagneticproperties,duetothemagneticcycloidspinstructureof62nminthismaterial [141].Latticedistortions,oxygenandbismuthvacancies,anddefectsattheinterfacesaswellasinsidegrainsarethesourcesofspacechargesinBiFeO3 [142].These spacechargesareabletofollowtheappliedfieldatlowerfrequencies,whereasthey cannotfindtimetoundergorelaxationathigh-frequencyregion[143,144].
1.7SpecificHeatandMagnetocaloricPropertiesof SomeManganite-BasedMultiferroicsforCryoCooling Applications
Duetotherestrictionsanddisadvantagesofthevaporcompressiontechnique, thescientificcommunityislookingatnewrefrigerationtechnologies,viz.thermoelectriccooling[145],adsorptionrefrigeration[146],absorptionrefrigeration [147],thermoacousticrefrigeration,andsolid-statemagneticrefrigeration.In recenttimes,thelargemagneticentropychangefoundinperovskitemanganites [148]suggeststhatthesematerialsmightbeexploitedformagneticrefrigeration
1.7SpecificHeatandMagnetocaloricPropertiesofSomeManganite-BasedMultiferroics 9 applications.Apartfromthis,therareearthmanganitesexhibitingmultiferroic behaviorhaveattractedattentionduetotheirpotentialapplicationsinmagnetic refrigerationindustry[15,149].Althoughresearchoncolossalmagnetoresistance andmultiferroicmanganitematerialswasinitiatedalmosttwodecadesback,this methodwasusedforthecalculationofmagnetocaloriceffectbyusingtemperature dependenceofspecificheatdataatdifferentmagneticfields[150,151].Ithasbeen reportedthatthemagnetocaloriceffect(MCE)determinedbythismethodhasthe sameaccuracyasthatfrommagnetizationmeasurements.Further,theaccuracyof thismethodisbetterthanthatofthedirectmethods.Atthetransitiontemperature, ananomalyinthedielectricbehaviorhasalsobeenobserved,indicatingcorrelation betweenthesebehaviors[152].Basedontheneutrondiffractionstudies[153],it wasreportedthatthesinusoidalorderingofMn3+ momentstransformsintoan incommensuratespiralorderatthistransition,whereMn3+ momentsarelocked. Thetransformationofsinusoidaltospiralmagneticorderingresultsinbreaking centerofsymmetry,which,inturn,leadstothepolarizationinthematerial.The transitionisalsoobservedindielectricconstantdataofthepresentinvestigation [154],whichisattributedtotheferroelectricity.Basedontheresultsofneutron diffractionmeasurementsofTbMnO3 sample,itisreportedthatthesinusoidal orderingofMn3+ momentstransformsintoanincommensuratespiralorder,which breaksthecenterofsymmetryofthesystemleadingtothespontaneouspolarization.Inthespecificheatstudiesofpresentinvestigation,yetanothertransition observedat24,27,and18Kisinfluencedbythemagneticfield.Atthistransition temperature,thecommensuratephasebecomeslow-temperatureincommensurate phase.Thesignatureofthismagnetictransitioncanalsobeseenindielectric constantbehaviorofthepresentinvestigation[155].Therefore,thisiscalledsecond ferroelectrictransition(T C2 ).
Sagaretal.[156]calculated ΔSM , ΔT ad ,andRCPofEuMnO3 atdifferentfields usingasimpletheoreticalapproach[157].Onlytemperature-dependentmagnetizationdata(M versus T )areneededinthismethod.Itwasobservedthatwith increasingfield,MCEparametersincreaselinearly[157].Severalscientificgroups alsoworkedonMCEofGdMnO3 ,TbMnO3 ,andDyMnO3 samplesintheirsingle andpolycrystallineforms.AdityaAWaghetal.[158]investigatedMCEproperties ofGdMnO3 singlecrystal.Theyusedmagneticandmagnetothermalmeasurements alongthethreecrystallographicaxesfortheinvestigationofMCEproperties. DyMnO3 ,whichcrystallizesinhexagonalform,wasalsostudiedbyBallietal. [159].Andcalculated ΔSM alongthec-directionandinabplaneatdifferentapplied magneticfieldvariation.Inc-direction,whenvaryingthemagneticfieldfrom0to 2T,0to5T,and0to7T,themaximumvariationoftheentropyreachesvaluesof5, 10,and13J/kg-K,respectively.Sattibabuetal.[160]alsoinvestigatedtheinfluence ofErdopingonmagnetocaloricperformanceofYbMnO3 sampleatdifferent fields.TheyusedtwosampleswithcompositionalformulaYb0.9 Er0.1 MnO3 and Yb0.8 Ho0.2 MnO3 andcalculatedusingheat-capacitydata.MCEparametersofthis systemincreasewithriseindopingconcentrationandfield,andarecomparable withreportedvalues.Forthefirstsampleinthisseries,the ΔSM valuesare1.81, 3.27,5.45,and7.26J/Kg-Kat2,4,6and8-Tfields.Multiferroicmanganiteswith
1NanostructuredMultiferroics:CurrentTrendsandFutureProspects orthorhombicandhexagonalstructureshowhighmagneticentropyandadiabatic temperaturechangesatbelow20K,whichisveryusefulforliquefactionofgases forcryocoolingapplications.The ΔS distributionofthesamplesisuniform,andit isdesirableforanEricsson-cyclemagneticrefrigerator,whichisbeneficialforthe householdapplicationofactivemagneticrefrigerantmaterials.
1.8Preparations,Characterization,andApplicationsof MultiferroicNanocomposites
Manypreparationmethodshavebeenadoptedinordertoproducehigh-quality materialsexhibitingmultiferroicpropertiesatroomtemperature.Salamietal.[161] prepared(1 x )Bi2 Fe4 O9 x CoFe2 O4 (0.0 ≤ x ≤ 1.0)multiferroicnanocomposites; thesenanocompositeshavebeenpreparedbywetchemicalprocedurescombining reversechemicalcoprecipitationandPechini-typesol–geltechniquesfollowedby mechanicalblendingprocess.Theauthorshavecharacterizedallnanocomposites withXRDandSAED,andtheresultsshowthatthediffractionpatternswere perfectlyindexedtotheconstituentphasespresentincompositesamples.Also, thecharacteristicpeaksinFTIRspectraconfirmedformationandpurityofall specimens.Manypreparationmethodshavebeenadoptedtoproduceartificial high-qualitymaterialsexhibitingmultiferroicpropertiesatRT[162–165].One interestingapproachistosynthesizecompositematerialswithonecomponent beingferroelectricandthesecondonebeingferromagneticatRT[166–168]. Mitraetal.[169]havecombinedphasesofGdMnO3 (GMO)andCoFe2 O4 (CFO) inthenanocompositestateandshowedsomelimitationsasmultiferroics.The authorshavereportedhighdielectricloss,thoughmagneticorderingisfound atRT,whiletheTiO2 matrixhoststheGMOandCFOwherethedielectricloss hasbeenremarkablyloweredandthedielectricandferroelectricordering(below ∼13K)ofGMOalongwiththemagneticphaseofCFOareutilizedtodevelopthe multiferroic.Mandaletal.[170]investigatedMEcoupling,dielectric,andelectrical propertiesof x La0.7 Sr0.3 MnO3 (LSMO) (1 x )Pb(Zr0.58 Ti0.42 )O3 (x = 0.05and0.1) multiferroicnanocomposites.Duongetal.[171]discussedaboutthegrowthof79% Bi2 Fe4 O9 –21%Fe3 O4 nanocompositefilmsonLaAlO3 substratesusingmolecular beamepitaxy.X-raydiffractionandfieldemissionscanningelectronmicroscopy confirmedthatthenanocompositesconsistedofanorthorhombicphaseoflamellae Bi2 Fe4 O9
RajeshBabuandKoduriRamam,[172]reportedsynthesis,structural,magnetic, anddielectricstudiesofRuthenium(Ru)-dopedBKFO(BiKFe2 O5 )multiferroic nanocomposite.Ajithetal.[173]preparedandcharacterizedMEmultiferroic BCZT–CFOnanocompositesthatweresynthesizedviasol–gelroute.XRDmeasurementsandTEMmeasurementswereconducted,andtheyindicatethatthemajority ofparticlesformed,havecore–shellstructure.Tangetal.[174]preparedenhanced MEresponseforLa0.67 Sr0.33 MnO3 /PbZr0.52 Ti0.48 O3 multiferroicbilayerthinfilm atRT;thesenanocompositeshavebeenpreparedusingpulsedlaserdeposition method.VivekVermaetal.[175]proposedimprovedmagneticpropertiesof
Bi0.9 Pr0.1 FeO3 intheircompositesofBPFOxNZFO.Forthecompositessample BPFO–NZFO1,theMs.andMr.arehigherthanthosemeasuredfortheBPFO andcontinuouslyincreasewiththeincreasingweightpercentageofNZFOin composites.Mahalakshmietal.[176]preparedandcharacterizedthemultiferroic compositesofCoFe2 O4 andBaTiO3 .Thesenanocompositeshavebeensynthesizedbycoprecipitationmethod.Hajlaouietal.[177]preparedandcharacterized high-qualityBa2 NdFeNb4 O15 -basedmultiferroicnanocompositefilmsthatwere grownonPt/MgO(100)singlecrystallinesubstrates.TuningofMEcouplingin multiferroicsisofgreatfundamentalandtechnologicalimportanceduetothe potentialapplicationsofMEeffectinadvanceddevices,suchasMEread-head sensors[178,179],datastorages[1,180,181],andspintronicdevices[12,107].
MultiferroicnanocompositescanfindvariousapplicationsinmagneticmaterialscoveringsensitiveHsensors,includingbiomedicalsensing,navigation,magnetoresistance(MR)applications,andmanymorecomplexapplicationsinspintronics [182].
1.9Conclusions
NanostructuredMultiferroicmaterialsoffergreatprospectsatmanyapplication levelsowingtotheiruniqueproperties.Inthischapter,wehavereviewedthe variousmultiferroicmaterialsandpreparation,characterizations,andapplications. Wehavealsoreviewedeachchapterthroughadetailedabstract.
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