Time-DomainMeasurementofUltrafastMagne4za4onDynamicsinMagne4c

Nanopar4cles

MastersofScienceThesisBrianEgenrietherNovember2015

Agenda

•  Introduc?onandpurpose•  Experimentalobjec?ves•  Theore?calintroduc?ons•  Induc?vetechniquedescrip?on•  Experimentaldetailsandconsidera?ons•  Resultsandinterpreta?ons•  Ques?ons

Introduc?onandPurpose•  Magne?cnanopar?clescomposedofmagne?te(Fe3O4)withadiameterof

10nmarestudied.•  Similarpar?clesareusedininvivomedicalimaging,magne?csensors,

drugdelivery,cancerresearch,andmicroscopicdiffrac?ongra?ngs(CrawfordGroup),etc.

•  Inprac?callyalloftheseapplica?ons,thepar?clesinteractwithfluctua?ngmagne?cfields.

•  Largeamountsoffrequency-domainresearchhasbeendoneonmagne?cnanopar?cles,howeveralmostno?me-domaindataexistsduetothesmallnessofthepar?clesandthehighspeedoftheprocess(~2ns).

•  Havinganideaofhowtheybehaveinthe?medomainyieldsabe[erunderstandingofhowtoemploytheminprac?ce.

•  Italsoservesthefieldofscien?ficinquiry.

ExperimentalObjec?ves•  Todetermineifcollec?onsofmagne?cnanopar?clesundergothe

precessiondynamicspredictedbytheLandau-Lifshitz(LL)theoryandifthese?me-domaindynamicscanbemeasuredbyamagne?cinduc?ontechniquetobedescribed.

•  Tofitthe?me-domaindatatoadampedsinusoidalsolu?ontotheLLequa?on.

•  Tocalculatethefrequency-domainresponsebyemployingaFastFourierTransformtothe?me-domaindata.

•  Tounderstandtheprogressionofthefrequencyasafunc?onoftheappliedmagne?cbiasfield.

•  Toes?matethephenomenologicaldampingparameterofthemagne?tepar?clesasafunc?onofappliedfieldandthespectroscopicspli]ngfactor(org-factor),ofthepar?cles.

LarmorEqua?on

TheLarmorequa?onpredictsmagne?za?onwillprecessaboutanexternalfieldindefinitelyinaplaneorthogonaltothefield.

Landau-LifshitzTheory

Induc?veTechniqueOverviewCoplanarwaveguideWithnanopar?clesample

RapidHfieldreorienta?on

Time-changingmagne?cfieldfrompar?cles

InducedvoltagebyFaraday’sLaw

Superparamagne?sm•  Smallmagne?cpar?cleshavemomentsthatfluctuatetheirorienta?ondueto

thermalexcita?ons.•  Forsinglepar?clesaboveacertaintemperature(the“blocking”temperature)the

netmagne?za?onoveranextended?meiszero.

•  Themagne?za?onisanonlinearfunc?onoftheexternalmagne?cfield.

•  ThiseffectcausestheM-Hcurveofthepar?clesto

close,exhibi?ngnoremanenceorcoercivity.

•  Fordensecollec?onsofinterac?ngpar?cleshowever,theeffec?veblockingtemperaturecanberaised,inducingamixed-stateofferrimagne?smandsuperparamagne?sm.

Superparamagne?sm•  Indensecollec?onsofinterac?ngpar?cles,thecurvemaynotcompletelyclose

norcrossiden?callyatzero.•  Themaximumvalueofmagne?za?onMsisfoundtobe532kA/m,whichisroughly

10%higherthanthetabulatedvalue.ErrorinFe3O4concentra?onorvolumetricmeasurementsofferrofluidcouldbethecause.

•  Par?cleshavealsobeenfoundtohaveahigherMsduetosurfaceeffects,buttheconversehasalsobeenfound.

TwoSampleGeometries

Circularsampleonwaveguide.

Stripsampleonwaveguide.

•  Twotypesofnanopar?clesamplegeometrieswereprepared.•  Ofthese,halfweredriedinadirectedmagne?cfield(2.5kA/m)andhalfwere

not.

ExperimentLayout

TemporalDricErrorCorrec?onToextracttheinduc?vesignalfromthestepvoltagewaveformsubtrac?vesynthesisisemployed.Astepsignalwithoutprecessionissubtractedfromonethathasprecession,leavingonlythedesiredinduc?vesignal.

TemporalDricErrorCorrec?on

“Zeroing”stepsignalisnotalignedin?mewith“Precession”stepsignalduetoaslightdricintriggersignal.

Thisintroducesrela?velylargevoltagespikesandanapparentlynoisysignal(red).Signalsmustbe?meshicedtocorrelatethembetween0Vand-2.5V.Thisyieldstheactualsignal(blue).

Time-DomainResults

Exampleofatypicalcorrectedmeasurement.Notethemeasuredvoltagesignaliss?llnotexactlyadampedsinewaveaspredicted.Why?

FFTResults

TwomainresonancepeaksareseenwhenanFFTisdoneon?me-domainresults.Theymustbothbeaccountedforina?medomaindatafit.Thelowfrequencymodeistheknownresonantfrequencyofmagne?tefromFMRexperiments.Thedefiniteoriginofthehighermodeispresentlyunknown.

FFT

Time-DomainDataFit

Time-DomainDataFit

Circularfield-drieddata,resultstypical.

Time-DomainDataFits

Circularfield-drieddata,resultstypical.

LowFrequencyMode

Circularfield-drieddata,resultstypical.

HighFrequencyMode

Circularfield-drieddata,resultstypical.

FrequencyDomainAnalysis

FrequencyDomainFitCircularField-DriedData

FrequencyDomainFitStripField-DriedData

FrequencyDomainFitCircularNonField-DriedData

FrequencyDomainFitStripNonField-DriedData

FrequencyDomainDiscussion•  Thedataarewellfi[edtotheKi[leequa?onofferromagne?cresonancewhere

thedemagne?zingfactorsareseentodescribespheres,nottheoverallsample.•  ThescalefactorKisfoundtobepropor?onaltotheHfield,notthe

magne?za?onM(H)aswasexpectedforademagne?za?onfield.Thisisnotpresentlyunderstood.

•  Thequan?tyHAmaybea[ributedtotheslightremanentfieldfoundearlierorpossiblytothemagnetocrystallineanisotropyfieldgivenby

•  Pu]ngthevaluesK1=13kJ/m3andMs=480kA/myieldsHA=43kA/m,whichiswithin10%ofallvaluesofHAfoundfromprecessiondataatHb=0.

•  IfthelargestvalueofMs=532kA/mfoundfromtheVSMisused,theerrorislessthan1%,howeverthismeasurementhas2poten?alvolumetricerrorsmen?onedearlier.

Field-DriedDamping

Circularfield-drieddamping. Stripfield-drieddamping.

•  Thelowmodedampinghasanearlymonotonicdecreaseasbiasfieldincreases.•  Thehighmodereachesaminimumatdifferentpointsandincreases

drama?cally.

NonField-DriedDamping

•  Thelowmodedampingforthestriphasanearlymonotonicdecreaseasbiasfieldincreasesbutthecircleincreases(asdoestheerror).

•  Thehighmodereachesaminimumatdifferentpointsandincreasesmuchlessthanforthefield-driedcase.

Circularnonfield-drieddamping. Stripnonfield-drieddamping.

Conclusions•  The?me-domainsignalsarewellfi[edtotwoexponen?allydampedsinusoids.•  Thelowfrequencyistheresonantfrequencyofmagne?te,theoriginofthehigher

modehasnotbeendefini?velyiden?fied.•  Thesamplesalldisplaybehaviorofnearlysphericalobjectsforbothfrequencies.•  Fielddryingversusnonfield-dryingthesampleshasli[leeffectontheprecession

frequenciesasdoessampleshape.•  Theg-factorswerefoundtoagreewellwiththepreviouslyreportedvalue.•  Thebiasfieldreduc?onwasnotfoundtobeafunc?onofthemagne?za?on.•  Lowfrequencydampinggenerallydecreaseswithincreasingbiasfield,aresult

similar(qualita?vely)toimpulseinduc?onexperimentsonthinfilms.•  Highfrequencydampingislargelyaffectedbyfielddrying.Itincreases

drama?callyathighbiasfields.•  Duetodampingalmostallofthedynamicshavedissipatedwithin2ns.

References1)  R.R.Shah,T.P.Davis,A.L.Glover,D.E.Nikkles,andC.S.Brazel,J.Magn.Magn.

Mater.387,96(2015).2)  M.Swierczewska,S.Lee,X.Y.Chen,Mol.Imaging10,3.3)  B.Gleich,J.Weizenecker,Nature435,1214(2005).4)  J.Kim,J.E.Lee,S.H.Lee,J.H.Yu,J.H.Lee,T.G.Park,T.Heyon,Adv.Mater.20,

478(2008).5)  B.G.KrugandJ.A.Asumadu,IEEE,15,4174(2015).6)  G.V.Kurlyandskaya,J.Cunanan,S.M.Bhagat,J.C.Aphesteguy,S.E.Jacobo,J.Phys.

Chem.Solids68,1527(2007).7)  DeBiasi,E.LimaJr.,C.A.Ramos,A.Butera,R.D.Zysler,J.Magn.Magn.Mater.

326,138(2013).8)  BenjaminP.Weissetal.Earth.Planet.Sci.LeG.224,73(2004).9)  Tamaru,J.A.Bain,R.J.M.vandeVeerdonk,T.M.Crawford,M.Covington,andM.

H.Kryder,J.Appl.Phys.,91,8034(2002).

References10)S.Kopyletal.J.Magn.Magn.Mater.358,44(2014).11)F.JOwens,J.Phys.Chem.Solids64,2289(2003).12) M.Grimsditch,G.K.Leaf,H.G.Kaper,D.A.Karpeev,R.E.Camley,Phys.Rev.B.69,

174428(2003).13) J.M.D.Coey,MagneKsmandMagneKcMaterials,CambridgePress,Cambridge

(2010),p.316.14) T.J.Silva,C.S.Lee,T.M.Crawford,andC.T.Rogers,J.Appl.Phys.85,7849(1999).15) L.Néel,Ann.Geophys.(C.N.R.S.)5,99(1949).16) M.F.Hansen,P.E.Jonsson,P.Nordblad,P.Svedlindh,J.Phys.:Condens.MaGer14,

4901(2002).17) D.Kechrakos,andK.N.Trohidou,J.Nanosci.Nanotechnol.8,2929(2008).18) J.Lee,R.Tan,J.Wu,andY.Kim,Appl.Phys.LeG.99,062506(2011).19) X.BatlleandALabarta,J.Appl.Phys.35R15-R42(2002).

References20) N.Songetal.Sci.Rep.3,3161(2013).21) C.Ki[el,Phys.Rev.73,155–161(1948).

Ques?ons?