schuller group - electrical and computer...

1

SCHULLER GROUP Nanoscience: Thin Film, Lithography

Magnetism: Exchange Bias, Tunneling, Transport

Superconductivity: Pinning,Photoinduced,Search

Superlattices: Metal, Organic, Oxides, Semicond.

Organics: Metallo-Phthalocyanines

Oxides: Transition Metals, Perovskites,

Applications: Sensors, Storage, Magnetic devices

Movies and Plays

http://ischuller.ucsd.edu

2

Enjoy the Process

•Caminante no hay camino, se hace el camino al andar.

Antonio Cipriano José María y Francisco de Santa Ana Machado y Ruiz

(26 July 1875 – 22 February 1939)

•Wanderer, there is no road,the road is made by walking.

3

VERY INTERESTING

50 100 150

-1.0

-0.5

0.0

0.5

1.0

M /

MS

Temperature (K)TN

AFFM

H HFC=1kOe

Proximity Between Dissimilar Magnets

Anomalous Spontaneous Reversal in Magnetic Heterostructures, Z.-P. Li, J. Eisenmenger, C. W. Miller and Ivan K. Schuller, Phys. Rev. Lett. 96, 137201 (2006).

UNDERSTANDING CRUCIAL

TN<< TC

4

PLEASE ASK QUESTIONSWhy ?

• Keeps you focused• Keeps you awake• You learn more• Develop interest

Feed Back Please

5

35 Years of

Metallic Superlattices

DOENSF, AFOSR, ONR

IVAN K. SCHULLER

IEEE Distinguished Lecturer

IEEE Magnetics Society Home Page: www.ieeemagnetics.org– 3000 full members– 300 student members

The Society– Conference organization (INTERMAG, MMM, TMRC, etc.)– Student support for conferences– Large conference discounts for members– Graduate Student Summer Schools– Local chapter activities– Distinguished lectures

IEEE Transactions on Magnetics– ~2000 peer reviewed pages each year– Electronic access to all IEEE Transactions on Magnetics papers

Online applications for IEEE membership: www.ieee.org/join– 360,000 members – IEEE student membership IEEE full membership

The Journal of Your Field

On line at ieeexplore.ieee.orgSubmit manuscripts at mc.manuscriptcentral.com/maglet‐ieee

Peer reviewed

Rapid publication

Worldwide circulation

IEEE Xplore archive

Four‐page articles

No page charges

8

Thank you

10

L. Esaki and R.Tsu, IBM J. Res. Dev. 14,61(1970)

35 years

of

Metallic Superlattices

(Fe/Cr)N Nb SiO2

I I

11

JUNIOR

UCSD ARGONNE LABS BELGIUMJose Colino Cornell Chun Kristian TemstKai Liu Hitoshi Homma Hans VanderstraetenMarie-Claire Cyrille Indrajit Banerjee M. GijsArjang Fartash M.R. Khan J.-P. LocquetIatneng Chan Yves Lepetre W. SevenhansAlberto Fernandes J. MurduckEric Fullerton T.R. WernerJosé M. Gallego Q.S. YangDoris Girata G.-G. ZhengElvira Gonzalez Jia-Qi ZhengJulio Guimpel Eric ZieglerSihong KimDavid LedermanChris LeightonJosé I. MartínTim MoranOsamu NakamuraMaría VélezJosep Nogués

LONG TERM

Yvan BruynseraedeRicardo RamirezMiguel KiwiJose VicentK.V. Rao

13

U C T )

T E

AP

PL

ICA

TIO

NS

Hard disk drives

MRAM

Sensors

SC

IEN

CE

Co

Cu

I

State: +1

State: 0

State: -1

-4 -3 -2 -1 0 1 2 3 4

-1

0

1 HFC (kOe) 0.5 2.0 5.0

M /

MS

H (kOe)

GMR SPIN TORQUE

EXCHANGEBIAS

14

Increased Exchange Anisotropy due to Interface Disorder in Permalloy/CoO, T.J. Moran, J.M. Gallego, and Ivan K. Schuller,

Jour. Appl. Phys. 78, 1887 (1995).

15Source: ISI Web of Knowledge, July 8, 2011

1960 1970 1980 1990 2000 20100

300

600

900

Total # of records: 7174

After 2000: 6062

Rec

ord

Cou

nt

Publication Year

"Exchange Bias" in topic

In 2050 everybodyWill be workingOn exchange bias

Unemployment Solved

16

PLAN• Introduction and History

• Characterization

• Interface Effects:

Structural length scale different from magnetic• Long Length Scales- Superlattice Effect:

Collective Magnons in M/N • Short Length Scales- Superlattice effects:

Oscillations in Resistivity• Future

17

One layer

Two layers

Three layers

Many layers, N

DisorderConfinementLower dimensionality

InterfacesElectron transferStrainsProximity effects

CouplingDimensional transitionsSpin Transmission

Superlattice effects

WHY DO ALL THIS ?

18

Metal

InsulatorConsequence

of thePeriodicity

Double Unit Cell

320 340 360101

102

103

104

105

106

107 100 nm VO2

film

Cooling

R(

)

Temperature (K)

Heating

19

VO2

~ 0.32% Volume Change

V2O3

100 120 140 160 180 200102

103

104

105

106

107

108

Cooling

R (

)

Temperature (K)

Heating

100 nm V2O3 film

1.4% Volume Change

Dimers to Single AFM to Para

Peierls Slater

20

DICTIONARY• Heterostructure(incoherent)

• Multilayer(long wavelength coherence)

• Superlattice(atomic scale coherence)

21

ATOMSSOLIDS

DUE TO THE ADDED PERIODICITYNEW EFFECTS APPEAR IN THE

ELECTRONIC PROPERTIES

FILMS SUPERLATTICES

SUPERLATTICE EFFECTS!

24

April, 1981

In 4 or 5 years, this will be THE field

in materials science.

25

METALLIC SUPERLATTICE

I.K.Schuller, Phys.Rev.Lett. 44, 1597(1980)

26

WHY CAREABOUT

STRUCTURE ?

27

STRUCTURE vs. PROPERTIES

• POSTULATEProperties of a solid are given by the atomic locations

• SMALL STRUCTURAL CHANGESLarge effects on Physical Properties

•EXAMPLE2% expansion in lattice 100% change in elastic constant

CHARACTERIZE QUANTITATIVELY AT THE ATOMIC SCALE

28

MAGNETISM

MgOFeFFeAl

2

glass

Untwinned TwinnedIn-plane

polycrystalline

FeF2

FeAl

ZnF2

bulk FeF2

MgOFeFFeAg

2

ALL 110 FeF2

29

EXCHANGE BIASED Fe/FeF2

J. Nogués, D. Lederman, I. K. Schuller, Appl. Phys. Lett. 68, 3186(1996)

30

STRUCTURE

“DETERMINE THE POSITIONS OF ALL THEATOMS IN THE MATERIAL”

Find out: - Expansions- Interdiffusion- Roughness- etc.

• ELECTRON MICROSCOPY• DIFFRACTION

31

Z

X-Y

1Å 10Å 100Å 1000Å 1m 10m

1Å 10Å 100Å 1000Å 1m 10m

Magnetism

Transport

Superconductivity

exchange

screeningRKKY dipolar

spin diffusionmean free path

coherencepenetration depth

ion mill surface analysis

x-ray diffractionneutron diffraction

transmission electron microscopy

x-ray diffractionneutron diffraction

transmission electron microscopyscanning electron microscopy

scanning probe microscopy

32

WHY CAREABOUT

STRUCTURE ?•Nothing is Perfect nor As Expected

•Small structural changes give BIG effects in

the Physical Properties

33MANY RED HERRINGS

34

-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

150 K

Long

Mom

ent (

emu)

Field (Oe)

-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

120 K

Long

Mom

ent (

emu)

Field (Oe)-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

110 K

Long

Mom

ent (

emu)

Field (Oe)-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

100 K

Long

Mom

ent (

emu)

Field (Oe)-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

80 K

Long

Mom

ent (

emu)

Field (Oe)-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

40 K

Long

Mom

ent (

emu)

Field (Oe)-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

10 K

Long

Mom

ent (

emu)

Field (Oe)

Field Cooling 1000 Oe

Py-V2O3 Bilayer

35

-3000 -2000 -1000 0 1000 2000 3000

-0.0005

0.0000

0.0005

10 K 40 K 60 K 70 K 80 K 90 K 100 K 110 K 120 K 150 K

Long

Mom

ent (

emu)

Field (Oe)

Field Cooling 1000 Oe

J. De la Venta, M. Erehkinsky, R. Morales, IKS, Phys. Rev. 2013

36

-800 -400 0 400 800

MO

KE (a

rb. u

nits

)

H (Oe)-400 -200 0 200 400

MO

KE (a

rb. u

nits

)

H (Oe)

Py (30 nm)

Py (30 nm)V2O3 (100 nm)

Kerr Effect

37

10 20 30 40 50 60 70 80 90 100

2 degrees)

* V2O3

▼FM (Py or Ni)

● New Phase●●

▼

▼●*

Py (30nm) /V2O3(100 nm)

Ni (30nm) /V2O3(100 nm)X-

Ray

Int

ensi

ty

Unexpected FeO phase

STRUCTURE IS IMPORTANT

38

NOTHING IS PERFECT

39

IF YOU MEASURE THEMPROPERLY

40

START

I.K.Schuller, Phys.Rev.Lett. 44, 1597(1980)

41Merci-Pierre Dhez

42

Capability Neutrons Synchrotron Electron Micr Scanning Probe

Magnetic structure ☺☺☺ ☺☺ ☺☺☺Element specificity ☺☺☺ ☺☺ ☺☺Isotope sensitivity ☺☺☺ ☺Energy tuning ☺☺☺ ☺☺Inelastic ☺☺☺ ☺ ☺Intensity ☺ ☺☺☺ ☺☺Time dependence ☺ ☺☺☺ ☺

TECHNIQUES & CAPABILITIES

43

Sample Neutrons Synchrotron E- microscopy Scanning Probe

Destructive ☺☺☺ ☺☺ ☺☺☺Smallest size ☺ ☺☺☺ ☺☺ ☺☺☺Homogeneity ☺ ☺☺☺ ☺☺Environment ☺☺☺ ☺☺☺ ☺

Heating ☺ ☺ ☺Interfaces ☺☺☺ ☺ ☺

SAMPLE VIEWPOINT

44

REFINEMENT

SUPREX: http//:ischuller.ucsd.edu

45

How well do we need to know the structure ???

Compare to Physical Length Scaleand ……….

Always remember limitations

PHILOSOPHYEffects are interesting either if they:

Cannot be explained as disorderOr

Connected quantitatively to the structure

46

47

Physics Driving Force

• Surfaces• Quantization

NANO, Nano, nano, nano

Proximity• Extension of

• Extension of M

STRUCTURAL DETERMINATION

QuantitativeAppropriate Length Scale

48

SMALL CHANGES IN THE STRUCTURECAN PRODUCE

LARGE EFFECTS IN THE PHYSICS

Remember limitations of techniques

49

Magnetic & Nonmagnetic Roughness

Mo/Ni SuperlatticesCollaborators

J. Cable, ORNLM. Khan, G. Felcher, ANL

50

Polarized Neutron ScatteringMo/Ni Superlattices

SquareModulation

ExperimentalFlippingRatio

All possiblemodels

51

Mo/Ni Superlattices

J. W. Cable, M.R. Khan, G. Felcher, I. K. Schuller, Phys. Rev. B34, 1643(1986)

“A comparison of X-ray and neutron diffraction implies that the magnetic profile in the superlattice is more perfect than the chemical profile.”

Mo

Ni

Mo

53

So six blind men of Hindustan disputed loud and long,Each in his own opinion exceeding stiff and strong;

Though each was partly in the right,

they all were in the wrong!

Syādvāda (Devanagari:

यादवाद)Jain Philosphy

55

SYSTEMATIC STUDIES ESSENTIAL

• Quantitative (Structure,….. )• Systematic (One parameter at a time)• Different measurements on same samples• Reevaluate (Even well accepted “facts”)

56

Axel Hoffmann Thesis

57

One layer

Two layers

Three layers

Many layers, N





WHY DO ALL THIS ?

58

Exchange Bias

FM

Free FMExchange field HE=0Small coercivity HCSymmetricUniform

FMAF

Pinned FMLarge HELarge HC

HE

2HC

H

M

H

M

59

AntiFerromagnetSURFACE OR BULK

Py

FeF2

Ni

Confirmed by Mossbauer, Synchrotron, Neut

60

200 nm

20 40 60 80 100

T (K)

FM/AF/FMParallel

PyFeF2

Ni

PyFeF2

Ni

Anti-parallel

20 40 60 80 100

0

100

200

300

400

HE

B (O

e)

T (K)

Ni

-2 -1 0 1 2

-1.0

-0.5

0.0

0.5

1.0

HvEB=66.5mT

HbEB=40.9mT

M/M

sMagnetic Field (kOe)

T=10K

Radiation Damage

62

Ferromagnet-Oxide

FMOXIDE

320 340 360101

102

103

104

105

106

107 100 nm VO2

film

Cooling

R(

)

Temperature (K)

Heating

63

VO2

~ 0.32% Volume Change

V2O3

100 120 140 160 180 200102

103

104

105

106

107

108

Cooling

R (

)

Temperature (K)

Heating

100 nm V2O3 film

1.4% Volume Change

-300 -200 -100 0 100 200 300

-400

-200

0

200

400

180 K 190 K 200 KM

agne

tizat

ion

(em

u cm

-3)

Magnetic Field (Oe)

100 150 200 250406080

100120140160180200220

Coe

rciv

ity (O

e)

Temperature (K)

Heating Cooling

Metal Insulator Transition + Structural Phase TransitionInterface Coupling in Ni/V2O3

Change of M and Hc at MIT and SPT

V2O3 (100 nm)

Ni (10 nm)

Al2O3 Substrate

-300 -200 -100 0 100 200 300

-400

-200

0

200

400

165 K 170 K 175 K 180 K 190 K 200 K

100 K 120 K 140 K 150 K 155 K 160 K

Mag

netiz

atio

n (e

mu

cm-3)

Magnetic Field (Oe)

100 150 200 250406080

100120140160180200220

Coe

rciv

ity (O

e)

Temperature (K)

Heating Cooling

64

-300 -200 -100 0 100 200 300

-400

-200

0

200

400

165 K 170 K 175 K 180 K 190 K 200 K

150 K 155 K 160 K

Mag

netiz

atio

n (e

mu

cm-3)

Magnetic Field (Oe)

100 150 200 250406080

100120140160180200220

Coe

rciv

ity (O

e)

Temperature (K)

Heating Cooling

-300 -200 -100 0 100 200 300

-400

-200

0

200

400

165 K 170 K 175 K 180 K 190 K 200 KM

agne

tizat

ion

(em

u cm

-3)

Magnetic Field (Oe)

100 150 200 250406080

100120140160180200220

Coe

rciv

ity (O

e)

Temperature (K)

Heating Cooling

65

One layer

Two layers

Three layers

Many layers, N





WHY DO ALL THIS ?

66

Magnetotransport in Superlattices

CollaboratorsC. Falco, ANL

J. Hilliard, J. Ketterson, B. Thaler, NorthwesternR. Lacoe, R. Dee, UCLA

67

In the Beginning …

69

e e-GMR in Fe/Cr superlattices

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

0

2

4

6

8

10

RP

RAP

BS

R/R

P[%

]

B [T]

M. N. Baibich et al Phys. Rev. Lett.61, 2472 (1988)

70

2007 PHYSICS NOBELGrunberg Fert

71

DON’T LET YOUR ELDERS DEPRESS YOU !!!!

•Pushing the Limits is Important•Make New Materials

•Something will happen

72

One layer

Two layers

Three layers

Many layers, N





WHY DO ALL THIS ?

73

PROPERTIES WHICH DEPENDON THE SUPERLATTICE NATURE ?

Relevant Length scale?

1. X-rays Sensitive to disorder !

2. Magnons Long length scaleDipolar ~ 200 Å

M. Grimsditch, M. Khan, A. Kueny, IKS, Phys.Rev.Lett. 51, 498(1983)

3. Resistivity Very high compared to bulkMonotonic vs. Periodicity (

RESISTORS IN PARALLEL

74

SUPERLATTICE EFFECTS IN THETRANSPORT PROPERTIES

COLLABORATORSSihong KimJ.M. GallegoD. Lederman

UCSD

Work supported byDOE

75

Why is this difficult ?

76

TROUBLEInterfacial Scattering Dominates

Nb/Cu Nb/Ti

77

ATOMSSOLIDS

DUE TO THE ADDED PERIODICITYNEW EFFECTS APPEAR IN THE

ELECTRONIC PROPERTIES

FILMS SUPERLATTICES

SUPERLATTICE EFFECTS!

78

SUMMARYDo what you like,

but above all like what you do

Francisco Schuller

79

One layer

Two layers

Three layers

Many layers, N





WHY DO ALL THIS ?

80

INTERESTING QUESTIONS1. Extended Electronic States?

• Signature

2. Interaction Effects?• Phase in Ferromagnetic/Superconducting

3. Confinement of Collective Excitations?• Magnons, Phonons, etc.

4. Proximity Effects?• Magnetism

5. Growth• Kinetics vs. Thermodynamics

6. Pinning

7. Spin Transport

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