ebook img

Nanostructured Materials for Magnetoelectronics PDF

228 Pages·2013·10.536 MB·English
Save to my drive
Quick download
Download
Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.

Preview Nanostructured Materials for Magnetoelectronics

Springer Series in Materials Science Volume 175 SeriesEditors RobertHull,Charlottesville,VA,USA ChennupatiJagadish,Canberra,ACT,Australia RichardM.Osgood,NewYork,NY,USA JürgenParisi,Oldenburg,Germany ZhimingM.Wang,Chengdu,P.R.China Forfurthervolumes: www.springer.com/series/856 TheSpringerSeriesinMaterialsSciencecoversthecompletespectrumofmaterialsphysics, including fundamental principles, physical properties, materials theory and design. Recog- nizingtheincreasingimportanceofmaterialsscienceinfuturedevicetechnologies,thebook titlesinthisseriesreflectthestate-of-the-artinunderstandingandcontrollingthestructure andpropertiesofallimportantclassesofmaterials. Bekir Aktas¸ (cid:2) Faik Mikailzade Editors Nanostructured Materials for Magnetoelectronics Editors BekirAktas¸ FaikMikailzade DepartmentofPhysics DepartmentofPhysics GebzeInstituteofTechnology GebzeInstituteofTechnology Gebze-Kocaeli,Turkey Gebze-Kocaeli,Turkey ISSN0933-033X SpringerSeriesinMaterialsScience ISBN978-3-642-34957-7 ISBN978-3-642-34958-4(eBook) DOI10.1007/978-3-642-34958-4 SpringerHeidelbergNewYorkDordrechtLondon LibraryofCongressControlNumber:2013930538 ©Springer-VerlagBerlinHeidelberg2013 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerptsinconnection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher’slocation,initscurrentversion,andpermissionforusemustalwaysbeobtainedfromSpringer. PermissionsforusemaybeobtainedthroughRightsLinkattheCopyrightClearanceCenter.Violations areliabletoprosecutionundertherespectiveCopyrightLaw. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublication doesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. Whiletheadviceandinformationinthisbookarebelievedtobetrueandaccurateatthedateofpub- lication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityforany errorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,withrespect tothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface Theresearch anddevelopmentof nanoscalemagneticmaterialsis oneofthemost promisingfieldsintoday’sscienceandisabasefornewbranchesofhigh-techin- dustry. In recent decades intensive investigations in this field have promoted great progressinthetechnologicalapplicationsofmagnetisminvariousareas.Nanoscale magnetic materials exhibit new and interesting physical properties that cannot be found in the bulk matter. Many of these unique properties have high potential for technicalapplicationsinmagneticstoragemedia,magneticheadsofcomputerhard disk drives, single-electron devices, microwave electronic devices, and magnetic sensors. New terminologies, such as magnetoelectronics and spintronics, have re- centlybeenintroducedtorefertoaspectsofthefieldinvolvingmagneticphenomena atthenanoscale. The technical progress of recent years involved the preparation of multilayer thinfilmsandnanowires,resultinginthediscoveryofthegiantmagnetoresistance (GMR)andtunnelmagnetoresistance(TMR)phenomena,consistinginanextraor- dinary change in the resistance/impedance of a material on application of an ex- ternalmagneticfield.GMRandTMRmaterialshavealreadyfoundapplicationsas sensors of low magnetic fields, computer hard disk read heads, magnetoresistive random access memory (RAM) chips, etc. The most recent investigations in the field of magnetic nanostructured materials introduced the new progressive field of spintronicdevices, whichutilize not only the electricalcharge but also the spin of electronsandopticalspinmanipulation. The dynamic behavioral features of magnetic nanostructures, especially the speed of magnetization reversal and the physical limitations, are crucial issues in magneticdatastorageandspintronics,astheydeterminethefunctionalityandfre- quencyresponseofdevices.Theneedtoincreasethedatatransferratesinmagnetic massstoragedevicespushestherelevantswitchingfrequenciesfarintothegigahertz (GHz)regime.Theenormouspowerdissipationincurrentsemiconductor-basedmi- croprocessorshasresultedinasearchforlow-poweralternatives,forexample,mag- neticlogiccircuits,whichprovidetheadvantageofaninherentdatanon-volatility. Thesuccessfuloperationoffuture“magneticprocessors”atGHzfrequenciesmust v vi Preface be based on careful control and tuning of the microscopic mechanisms governing themagneticswitchingprocess. Duringthelastdecade,spin-transfertorquephysicshasattractedmuchscientific interest after the transfer of spin momentum by spin-polarized currents was pre- dictedandobservedinthewakeoftheseminaldiscoveryofGMR,whichkickedoff the fast-paced developmentof spintronics. Whereas the GMR effect is well suited for sensing and detecting magnetization states, the spin-transfer torque provides a means to act on the magnetization, thus complementing GMR and extending the toolboxforspintronics. There are two different approaches for realizing spintronic devices. One is metal-based spintronics which uses ferromagnetic metals. The second one is semiconductor-based spintronics consisting of ferromagnetic semiconductors, for which much effort has focused on producing ferromagnetism in semiconductors above room temperature. If successful, this new class of spintronic devices could be integrated much more easily with conventional semiconductor technology. The keyrequirementinthedevelopmentofsuchdevicesistheefficientinjection,trans- fer, and detection of spin-polarized current from a ferromagnetic material into a semiconductor. Because of the well-known problem of a resistance mismatch at metal/semiconductorinterfaces,hinderinganeffectivespininjection,muchinterest isnowconcentratedonthedevelopmentofroom-temperatureferromagneticsemi- conductors. In recent years there has been a considerably growing interest in multilayered GMRnanostructuresduetotheirwidemagnetoelectronicsapplications.Obviously, themagneticanisotropyandinterlayerexchangecouplingplaythemostimportant roles in these structures. Oscillatory interlayer exchange coupling between ferro- magnetic layers is an indirect exchange interaction of localized spins in magnetic layers mediated by conducting electrons of nonmagnetic spacers. As the need for ultra highdensity datarecording increases,the size of the films used in spintronic applicationsmustdecrease.Therefore,accuratemagneticcharacterizationisoneof themajorissuesrelatedtomagneticmultilayerstructures. Anotherimportantfieldisthatofinterfacialphenomenainperovskiteoxidesu- perlattices, which have the potential to provide unique functional properties for a diverse range of applications, including sensing, energy conversion, and informa- tion technology. In these systems, the antiferromagnetic and ferromagnetic order parameters display dissimilar dependences on sublayer thickness and temperature duetothecompetitionbetweendifferentmagneticinteractions.Forasmallrangeof sublayerthicknesses,arobustspin-flopcouplingisobservedsuchthatthealignment of the magnetization of the ferromagnetic layer with a magnetic field leads to the reorientation of the magnetic moments in the antiferromagnetic layer to maintain theproperorientationbetweendifferentmoments. Thescienceandtechnologyoffunctionalnanostructuredmaterialsreceivedgreat impetus by the ability to produce structures on a sub-micrometer scale. Nanofab- rication and nanotechnology allowed the manipulation of materials and the engi- neering of innovative materials and devices, both for fundamental studies and for applications in various fields. One of the major obstacles in the miniaturization of Preface vii nanoelectronic devices has been the fabrication of interconnects having diameters compatible with the size of the devices they connect. In solid state electronics as wellasinnanoelectronics,interconnectingnanoormoleculardeviceshasremained a challenge for several decades. Although the search for feasible interconnects in nanoelectronics is continuing, nanosized Si nanowires appear to be an attractive 1Dmaterialbecauseoftheirwell-knownsilicon-basedmicroelectronicfabrication technologyandtheirabilitytobeuseddirectlyontheSi-basedchips.Electronicand spintronicdeviceswithconductinginterconnectsbetweenthemcanbefabricatedon asingleSinanowireatadesiredorder. Oneofthemosteffectivemethodsofnanotechnologyandnanofabricationisthe self-assembling of nanoparticles or nanospheres, a low-cost alternative patterning technology particularly well suited to the preparation of arrays of dots or anti- dots covering a surface area of several square millimeters (mm2) or larger. While nanoparticles with a sharp size (diameter) distribution can be synthesized by sev- eral bottom-up chemical processes, and can even be functionalized for different purposes,theirdispersionoverlargesubstratesresultsinwell-ordered,short-range periodic templates, with a lack of long-range order and without a precise orienta- tiononthemacroscopicscaleofthewholesample,oftheperiodicstructure.Self- assemblingofpolystyrenenanospheresisapowerfultechniquetopreparelargearea (several mm2) nanostructured thin films. Compared to conventional lithographic techniques, which have more resolution and are more versatile, but are limited to very small surface areas, self-assembling of polystyrene nanospheres allows the preparation of large nanostructured samples. This technique limits the shaping to onlycirculardotandantidotgeometrieswhichcanbeobtainedinahexagonalclose- packedconfiguration. Another prospective field for research and application of magnetic nanostruc- tures is the fabrication and investigation of magnetic nanoparticles for biomedical applications.Magneticnanoparticlehyperthermia(MNH)treatmentoftumorsisat anadvancedstageofdevelopment;ithasbeenthroughphaseIhumanclinicaltri- als and is currently being tested in phase II in combination with other therapies. Currently the use of MNH for the treatment of tumors is restricted by the heating performance of the available nanoparticle ferrofluids. Although a massive amount ofimportantbiochemicalandclinicalworkisalsorequiredtodevelopthistherapy, theheatingissueisfundamentalandmustbesolved.Ofcourse,thisisjustthestart oftheprocess,asthemagneticnanoparticlesmustbemadebiocompatible,hidden fromtheimmunesystem,targeted,testedinvivo,etc.,butitisclearthatMNHwill be able to make significant strides towards becoming a stand-alone treatment, and thatitispotentiallyaverylowmorbidityandgenerictherapy. This book is intended to provide a review of the latest developments and the fundamentalconceptsintheabove-mentionedfieldsofresearchandapplicationof nanostructured magnetic materials as well as in the emerging fields of magneto- electronics and spintronics. The idea for this book was born at the Fifth Interna- tionalConferenceonNanoscaleMagnetism(ICNM-2010)heldonSeptember28– October2,2010inGebze-Istanbul,Turkey.ThemeetingwasorganizedbytheDe- partment of Physics of the Gebze Institute of Technology (GIT). The scope of the viii Preface contributionsextendsfromfundamentalmagneticpropertiesatthenanometerscale to fabrication and characterization of nanoscale magnetic materials and structures aswellasthephysicsbehindthebehaviorofthesestructures. Wewouldliketothankalltheauthorsfortheircontributions.Wealsoacknowl- edgethegreateffortsofourcollaboratorsandresearchfellowsfromtheDepartment ofPhysicsandNanomagnetismandSpintronicsResearchCenter(NASAM)ofGIT and others who made major contributions to the organization of the ICNM-2010 Conferenceandmadethispublicationpossible.WeareverygratefultoProf.C.As- cheronforhisgreatsupport,help,andpatienceduringthepublishingofthisbook. Gebze-Kocaeli,Turkey B.Aktas¸ F.Mikailzade Contents 1 FromMagnetodynamicstoSpinDynamicsinMagnetic Heterosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 ClausM.Schneider 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 MagnetodynamicImagingonthePicosecondTimeScale . . . . . 3 1.2.1 Time-ResolvedPhotoemissionMicroscopy . . . . . . . . . 3 1.2.2 ImagingMagnetizationDynamicsinSingleMagnetic ThinFilms . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.3 ImagingMagnetizationDynamicsinInterlayer-Coupled Trilayers . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.3 AddressingtheFemtosecondTimeScale . . . . . . . . . . . . . . 12 1.3.1 FemtosecondPulseSoftX-RaySources . . . . . . . . . . 13 1.3.2 MagnetodichroicEffectsintheEUVRegime . . . . . . . . 14 1.3.3 HHGPump-ProbeExperiments . . . . . . . . . . . . . . . 16 1.3.4 FutureDevelopment . . . . . . . . . . . . . . . . . . . . . 19 1.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2 Spin-TransferTorqueEffectsinSingle-CrystallineNanopillars . . . 25 D.E.Bürgler, R.Lehndorff, V.Sluka, A.Kákay, R.Hertel, and C.M.Schneider 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.2 Spin-TransferTorque(STT) . . . . . . . . . . . . . . . . . . . . . 27 2.2.1 Phenomenology . . . . . . . . . . . . . . . . . . . . . . . 27 2.2.2 Physical Picture: Absorption of the Transverse Spin CurrentComponent . . . . . . . . . . . . . . . . . . . . . 29 2.2.3 Slonczewski’sModel . . . . . . . . . . . . . . . . . . . . 32 2.3 SampleFabrication . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3.1 MBEGrowthofSingle-CrystallineMultilayers. . . . . . . 34 2.3.2 LithographicProcess . . . . . . . . . . . . . . . . . . . . 35 2.4 NormalandInverseCurrent-InducedSwitchinginaSinglePillar . 36 2.4.1 EvidenceforMagnetocrystallineAnisotropyinNanopillars 37 ix x Contents 2.4.2 NormalandInverseSwitching. . . . . . . . . . . . . . . . 38 2.5 InterplayBetweenMagnetocrystallineAnisotropyandSTT . . . . 40 2.5.1 Two-StepSwitchingProcess . . . . . . . . . . . . . . . . 40 2.5.2 Zero-FieldExcitationsinthe90°-State . . . . . . . . . . . 43 2.6 STT-DrivenVortexDynamicsinNanopillars . . . . . . . . . . . . 45 2.6.1 MagneticVorticesinNanopillars . . . . . . . . . . . . . . 46 2.6.2 UniformStateVersusVortexState . . . . . . . . . . . . . 47 2.6.3 InjectionLockingoftheGyrotropicVortexExcitation . . . 49 2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3 OriginofFerromagnetisminCo-ImplantedZnO . . . . . . . . . . . 57 NumanAkdogˇanandHartmutZabel 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.3 SamplePreparation . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.4 StructuralProperties . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.5 MagneticProperties . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.5.1 RoomTemperatureMagnetizationMeasurements . . . . . 65 3.5.2 XRMSandXASMeasurements . . . . . . . . . . . . . . . 65 3.5.3 Temperature-DependentMagnetizationMeasurements . . . 71 3.5.4 Magnetic Moment per Substituted Co Atom and EstimationofT . . . . . . . . . . . . . . . . . . . . . . . 73 c 3.5.5 FMRMeasurements . . . . . . . . . . . . . . . . . . . . . 74 3.6 AnomalousHallEffectMeasurements . . . . . . . . . . . . . . . 76 3.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 3.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 4 Magnetic Characterization of Exchange Coupled Ultrathin MagneticMultilayersbyFerromagneticResonanceTechnique. . . . 85 BekirAktas¸,RamazanTopkaya,MustafaErkovan,andMustafaÖzdemir 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 4.2 TheoreticalModel . . . . . . . . . . . . . . . . . . . . . . . . . . 89 4.2.1 MagneticFreeEnergy . . . . . . . . . . . . . . . . . . . . 89 4.2.2 DynamicEquationforMagnetization . . . . . . . . . . . . 91 4.2.3 SolutionofDynamicEquationforACMagnetization . . . 94 4.2.4 MagneticSusceptibility . . . . . . . . . . . . . . . . . . . 95 4.2.5 Computer Calculation of FMR Spectra to Get Fitted Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 96 4.3 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 4.3.1 SamplePreparation . . . . . . . . . . . . . . . . . . . . . 97 4.3.2 FMRandDCMagnetizationMeasurements . . . . . . . . 98 4.4 ExperimentalResultsandCalculations . . . . . . . . . . . . . . . 98 4.4.1 Three-LayeredPy/Cr/PyFilms . . . . . . . . . . . . . . . 98 4.4.2 Py/Cr/PyMultilayer . . . . . . . . . . . . . . . . . . . . . 108 4.5 OverallEvaluations . . . . . . . . . . . . . . . . . . . . . . . . . 114

See more

The list of books you might like

Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.