The magnetic shape memory alloy Ni-Mn-Sn in thin films

120 Pages·2012·3.54 MB·English

DOCTORALTHESISINPHYSICS
The magnetic shape memory alloy Ni-Mn-Sn in
thin films
AlexanderAuge
DepartmentofPhysics
UniversityofBielefeld
July2012
Declaration
Iwrotethisthesisbymyselfandusednonebuttheindicatedresources. Text
andfigureswerepartlytakenfromcorrespondingpublications,whichoriginate
directlyfromthiswork.
Bielefeld,July2012
(AlexanderAuge)
Reviewers
Prof. Dr. AndreasHu¨tten
Prof. Dr. ThomasHuser
Dateofsubmission: July2012
Dedicatedtothecurious
Publications
[1] A.Auge,A.Weddemann,F.Wittbracht,A.Hu¨tten: Magneticratchetfor
biotechnologicalapplications;Appl.Phys.Lett.94,183507(2009)
[2] A. Weddemann, F. Wittbracht, A. Auge, A. Hu¨tten: A hydrodynamic
switch: Microfluidicseparationsystemformagneticbeads;Appl.Phys.
Lett.94,173501(2009)
[3] C.Albon,A.Weddemann,A.Auge,A.Hu¨tten: Tunnelingmagnetoresis-
tancesensorsforhighresolutiveparticledetection;Appl.Phys.Lett.95,
023101(2009)
[4] C. Albon, A. Weddemann, A. Auge, D. Meißner, K. Rott, P. Jutzi, A.
Hu¨tten:Numbersensitivedetectionanddirectimagingofdipolarcoupled
magneticnanoparticlesbytunnelmagnetoresistivesensors;Appl.Phys.
Lett.95,163106(2009)
[5] A. Weddemann, A. Auge, C. Albon, F. Wittbracht, A. Hu¨tten: On the
resolutionlimitsoftunnelmagnetoresistancesensorsforparticledetection;
NewJ.Phys.11113027(2009)
[6] A.Weddemann,A.Auge,D.Kappe,F.Wittbracht,A.Hu¨tten: Dynamic
simulationsofthedipolardrivendemagnetizationprocessofmagnetic
multi-corenanoparticles;J.Magn.Magn.Mater.322,643-646(2009)
[7] A.Auge,A.Weddemann,B.Vogel,F.Wittbracht,A.Hu¨tten: Alevelset
based approach for modeling oxidation processes of ligand stabilized
metallicnanoparticles;Appl.Phys.Lett.96,093111(2010)
[8] A. Weddemann, B. Eickenberg, F. Wittbracht, A. Auge, A. Hu¨tten: A
combinedreaction-separationlab-on-a-chipdeviceforlowPecletnumber
applications;J.Appl.Phys.106,024510(2009)
[9] A.Weddemann,F.Wittbracht,A.Auge,A.Hu¨tten: Positioningsystemfor
particlesinmicrofluidicstructures;MicrofluidNanofluid7,849-855(2009)
[10] A. Weddemann, A. Auge, C. Albon, F. Wittbracht, A. Hu¨tten: Toward
the magnetoresistive detection of single magnetic nanoparticles: New
strategiesforparticledetectionbyadjustmentofsensorshape; J.Appl.
Phys.107,104314(2010)
[11] O.Schebaum,D.Drewello,A.Auge,G.Reiss,A.Thomas: Tunnelmag-
netoresistanceinalumina,magnesiaandcompositetunnelbarriermag-
netictunneljunctions;J.Magn.Magn.Mater.323,1525-1528(2011)DOI:
10.1016/j.jmmm.2011.01.011
[12] A.Weddemann,F.Wittbracht,A.Auge,A.Hu¨tten:Particleflowcontrolby
induceddipolarinteractionofsuperparamagneticmicrobeads;Microfluid
Nanofluid10,459-463(2011)
[13] A.Weddemann,C.Albon,A.Auge,P.Hedwig,D.Akemeier,K.Rott,D.
Meißner,P.Jutzi,A.Hu¨tten: Howtodesignmagneto-basedtotalanalysis
systemsforbiomedicalapplications;Biosensors&Bioelectronics26,1152-
1163(2010)
[14] I.Ennen,S.Lo¨ffler,C.Ku¨bel,D.Wang,A.Auge,A.Hu¨tten,P.Schattschnei-
der: Site-specificchiralityinmagnetictransitions;J.Magn.Magn.Mater.
324,2723–2726(2012)
[15] A.Auge,N.Teichert,M.Meinert,G.Reiss,A.Hu¨tten,E.Yu¨zu¨ak,I.Dincer,
Y.Elerman,I.Ennen,andP.Schattschneider: Thicknessdependenceof
the martensitic transformation, magnetism, and magnetoresistance in
epitaxialNi-Mn-Snultrathinfilms,Phys.Rev.B85,214118(2012)
Conferences
[1] A.Auge,T.Weiß,D.Akemeier,F.Wittbracht,A.Weddemann,A.Hu¨tten:
Micrototalanalysissystem: Acombinationofamagneticratchetwithgi-
antmagnetoresistancesensors;Biosensors2010,Edinburgh,GreatBritain
[2] A.Auge,A.Weddemann,B.Vogel,F.WittbrachtandA.Hu¨tten:Oxidation
ofmetallicnanoparticles;ComsolConference2009,Mailand,Italy
[3] A.Auge,N.Teichert,M.Meinert,I.Ennen,I.Dincer,E.Yuzuak,Y.Eler-
man, A. Hu¨tten: Martensitic transformation and magnetoresistance in
off-stoichiometricNi-Mn-Snthinfilms;Intermag2011,Taipeh,Taiwan
[4] A.Auge,N.Teichert,M.Meinert,I.Ennen,I.Dincer,E.Yuzuak,Y.Eler-
man,I.Ennen,P.Schattschneider,A.Hu¨tten: Martensitictransformation
andelectronenergylossmagneticchiraldichroisminoff-stoichiometric
Ni-Mn-Snthinfilms;APMAS2011,Antalya,Turkey
[5] A.Auge,N.Teichert,A.Hu¨tten: PhaseFieldSimulationsofMartensitic
TransformationinThinFilms;DPG2012,Berlin,Germany
Contents
Publications iv
Conferences vi
Contents vii
1 Introduction 1
2 FundamentalBasicsofMartensiticTransformations 5
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 PhaseCompatibility . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 MartensiticTransformationinrealcrystalsandthinfilms . . . . 16
2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3 Analyticalandpreparationtools 20
3.1 Thinfilmdeposition . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2 X-RayDiffractionandReflectometry . . . . . . . . . . . . . . . . 21
3.3 ChemicalcompositionanalysisbyX-RayFluorescence . . . . . 23
3.4 Electrictransportmeasurements . . . . . . . . . . . . . . . . . . 23
3.5 MagneticMeasurements . . . . . . . . . . . . . . . . . . . . . . . 23
4 PhaseFieldSimulations 24
4.1 Phasefieldmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.3 Simulationsofthinfilms-Geometry,approximationsandsolution 28
4.4 SummaryandDiscussion . . . . . . . . . . . . . . . . . . . . . . 35
5 Ni-Mn-Sninthinfilms 37
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.2 Structureintheaustenitephase: thinfilmquality. . . . . . . . . 41
5.3 Martensiticstructure . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.4 Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.5 Electricaltransport . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.6 Analysisofthemartensitictransformation. . . . . . . . . . . . . 75
5.7 Originsofthetransformationbehavior . . . . . . . . . . . . . . . 79
5.8 Magnetoresistance . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6 SummaryandConclusions 95
7 Outlook 98
Bibliography 99
8 Danksagung 111
1 Introduction
Thefunctionalbehaviorofshapememoryalloysasusedfor,e.g.,actuatorsand
switchingdevices,isrelatedtothestructuralinstabilityknownasmartensitic
transformation (MT). It is defined as a displacive, diffusionless first-order
solid to solid phase transformation from the high temperature austenite to
thelowtemperaturemartensitephase. Ferromagneticshapememoryalloys
(FSMA)arematerialsthatcombinetheshapememoryeffectandferromagnetic
behavior. TheHeusleralloysNi MnGaandoffstoichiometricNi Mn Z ,
2 50 25+x 25-x
whereZ=In,Sn,Sb,areimportantexamplesofFSMAduetotheirinteresting
physical phenomena such as large magnetic field induced strain,[1] giant
magnetocaloriceffects,[2]andgiantmagnetoresistance.[3]
Forapplicationssuchasactuators,magneticcoolingandhybridsystems,
thinfilmsareoftenadvantageousormandatory. Itwasshownthatshapemem-
oryalloysinthinfilmscanbeusedasmicrofluidicvalves,micropumpsand
microgrippers.[4]Formagneticcoolingdevices,thinfilmsoffertheadvantage
ofahighsurfacetovolumeratio. Thisallowsafastheattransfer.
AgeneralknowledgeofthethinfilminfluenceontheMTisrequiredfor
alltheseapplications. Theoreticalandexperimentalstudieshaveshown,that
thetransformationbehavioraswellasthemicrostructurechangessignificantly
inthinfilms.[5,6]Ininvestigationsonthetransformationbehavior,abroader
transitionandachangeinthetransitiontemperatureshasbeenfound. The
broadeningofthetransitionaswellasareducedtransitiontemperaturecanbe
causedbysubstrateconstraints,[7]confinementofthenucleusandsizescale
effectsonthethemeanfreepathoftransformationdislocations.[6]Anincrease
inthetransitiontemperaturecanbeattributedtostressinducedbythelattice
mismatchbetweensubstrateandthinfilm.[5]
1
1. INTRODUCTION
Thedetailsofthemicrostructuredependstronglyonmaterialproperties
andexternalinfluences. Inthinfilmsthesubstrateaswellasinducedtexture
playamajorrole. Thedegreeandkindoftexturehasalargeinfluenceonthe
allowedvariants.[8]Arigidsubstrateleadstosymmetrybreakingeffectsin
thesensethatnotallorientationsoftheaustenite-martensiteinterfacesallow
coarseningofnanotwinnedmartensitetomacroscopicnonmodulatedvariants.
[9]
Systematic studies on the influence of the film thickness on the MT are
sparseinliterature. EpitaxialNi-Mn-Gafilmshavebeeninvestigatedinthe
thicknessrangeof150nmto500nmwithvaryingcomposition.[9]Anincreas-
inginfluenceofthesubstratewithdecreasingthicknesshasbeenfounddue
tostressinducedmartensiteattheinterface. PolycrystallineNi-Mn-Snfilms
grownonSihavebeeninvestigatedinthethicknessrangefrom120nmupto
2.5µmbyVishnoietal. [10]TheyfoundasuppressionoftheMTbelow410nm
andanincreasingtransitiontemperaturewithincreasingfilmthickness. Most
otherstudiesontheMTinthinfilmsinvestigatedasinglefilmthicknessinthe
rangeofseveral100nmuptoseveral µm. [5,11,12,13,14]
Thisworkhastheoreticalaswellasexperimentalaspects. Atfirst,phase
field simulations are carried out for the well known model system NiAl in
thin films. This allows us to study the influence of a rigid substrate on the
martensitictransformationandtheinvolvedenergytermsfordifferentfilm
thicknesses. Thesecondpartofthisthesisinvolvesexperimentalstudiesof
Ni-Mn-Sn. ThisisaHeusleralloywithaverylowlatticemismatchof0.7%
withrespecttoMgO.[15]Thus,alowstressinfluencecanbeexpectedandthis
systemshouldbeanidealcandidatetostudytheinfluenceofconfinementand
sizescaleeffects. Twosampleserieswithdifferentcompositioninthethickness
rangeof200nmdownto10nmareinvestigatedusingtemperaturedependent
X-raydiffraction,magnetizationandresistivitymeasurements.
Thisthesisisorganizedasfollows:
1. Theoretical Basics: The martensitic transformation is introduced. The
basicsofmartensiticstructures,theinvolvedenergytermsandtheorigin
ofthemicrostructureisexplained. Theinfluenceofphasecompatibility,
sample quality and the thin film geometry on the phase transition is
introduced.
2