Spintronics --- Half metal Colossal Magnetoresistancespin/course/97/20080501.pdf · Spintronics --- Half metal and Colossal Magnetoresistance Jauyn Grace Lin Cener for Condensed Matter

____________________________________________________

Spintronics --- Half metaland

Colossal Magnetoresistance

Jauyn Grace Lin

Cener for Condensed Matter sciencesNational Taiwan Univsersity

2008/05/01

____________________________________________________

Chapter One

Half Metal

____________________________________________________Outline

1. Definition of half metal2. Material classification3. Polarization measurement4. Applications

Half metals are the extreme case of strong ferromagnet, where not only 3d electrons are fully polarized, but also other (sp) down-spin bands do not crossthe Fermi level.(examples: NiMnSb, PtMnSb--- Hesuler phases.)

JOURNAL OF APPLIED PHYSICS VOLUME 91 (2002)

Half-metallic ferromagnetism: Example of CrO2 (invited)J. M. D. Coey and M. Venkatesan

Physics Department, Trinity College, Dublin 2, Ireland

A half metal is a solid with an unusual electronic structure. For electrons of

one spin it is a metal with a Fermi surface, but for the opposite spin there is a

gap in the spin-polarized density of states, like a semiconductor or insulator.

This definition presupposes a magnetically ordered state to define the spin

quantization axis. The responses of a half metal to electric and magnetic field

at zero temperature are quite different. There is electric conductivity, but no

high-field magnetic susceptibility.

(CrO(CrO22,NiMnSb),NiMnSb)(Sr2FeMoO6)(Sr2FeMoO6)

(Magnetite)(Magnetite)(La(La0.70.7SrSr0.30.3MnOMnO66))

((GaAsMnGaAsMn))

(Tl(Tl22MnMn22OO77))(Doped (Doped EuOEuO & & EuSEuS))

FIG. 1. Schematic density of states for a half metal, (a) Type IA with only ↑ electrons at EF and (b) Type IB with only ↓ electrons at EF . In narrow d bands, the states at EF may be localized (type II).

FIG. 2. Schematic density of states for (a) a type IIIA half metal, whereelectrons of one spin direction are itinerant and the others are localized, (b)a semimetal, (c) a type IVA half metal, and (d), (e) two types of ferromagneticsemiconductor.

Definition of polarization Definition of polarization

νν: : fermifermi velocity of electronsvelocity of electrons

------ straightforwardstraightforward

------ real measurementreal measurement

FIG. 3. Comparison of five methods of measuring P: Photoemission, tunneljunction, point contact, Tedrow–Meservey experiment, Andreev reflection.

1.Photoemission1.Photoemission

2. 2. MagnMagn. Tunnel . Tunnel JuncJunc..

3. Point Contact3. Point Contact

4. 4. TedrowTedrow--MeserveyMeservey

5. 5. AndreevAndreev

FIG. 5. Spin polarization of the density of states of CrO2.

ΔΔSfSf : spin: spin--flip gapflip gap

FIG. 6. Resistivity of CrO2 thin films.

ρρoo= 4= 4××1010--88 ohmohm--mm~ 90 nm mean~ 90 nm mean--free pathfree path

ρρ = = ρρ oo TT22 ee--ΔΔ/T/T

with with ΔΔ ~ 80K~ 80K

FIG. 7. Magnetoresistance of a CrO2–Cr2O3 pressed powder compact, withtemperature dependence shown in the inset.

MRMR= [R(H)= [R(H)--R(0)]/R(0)R(0)]/R(0)= P= P22/(1+P/(1+P22))

a. Magneto-optical effectsLarge Kerr rotation in PtMnSb.

b. GMR applicationsSpin-valve system --- pick-up head, MRAM

c. Spin electronics--- Injection of polarized carriersi) The spin injection in a normal metal can give information on

the spin diffusion length in this metal.ii) Spin injection may act as a pair-breaking agent in a super-

conductor.iii) Half metals can also be used to build a spin transistoriv) Another possible application is as polarized tips in STM,

in order to visualize the orientation of magnetic domains.

Applications of Half metals

____________________________________________________

Chapter Two

Colossal Magnetoresistance

____________________________________________________Outline

1. Introduction2. Material3. Physical Properties4. Experiments

a. bulkb. film, bilayers

1. Introduction ---何謂電阻(率)

電阻 Rρ = R*A/w

ρ ρ ρ

T金屬半導體超導體

e-

____________________________________________________

Introduction ---物質的基本磁性

順磁

鐵磁

斜磁

反鐵磁

亞鐵磁

____________________________________________________

Introduction ---何謂磁阻

H = Ha

H = 0 大電阻

小電阻

____________________________________________________

____________________________________________________Introduction --- 何謂龐磁阻(CMR)

1) Very high magnetoresistance(99% at Tp)

2) Polarization 100% (half metal)

3) M- I (F/AF) transition4) Phase separation5) Charge ordering6) Orbital ordering

S. Jin et al. Science 265 (1994)

MR =[ρ(H)-ρ(0)]/ρ(H=6 tesla )

Type MR Field Temp. Sample

OMR 0.01% ~Tesla RT Cu,Al

AMR 2 ﹪ 10 Oe RT Fe,Co,Ni

GMR 10 ﹪ 2 Oe RT Fe/Cr/Fe

CMR 10 (99)% ~Tesla RT(LT) La-Sr-Mn-O

TMR 40 ﹪ 10 Oe RT Co/AlO/Co

____________________________________________________MR ratio of MR ratio of spintronicspintronic materialsmaterials

c=7.77ÅLa,Sr

La, Sr

Mn+3

b=5.5Å

a=5.471Å

2. Material PerovskitePerovskite layered structurelayered structure

LaMnO3: Cubic (insulator,Antiferromagnetic)

(La,Sr)MnO3: orthorhombic

(Metal, Ferromagnetic)

(0.70 (0.70 Å))(1.32 (1.32 Å))(1.216 (1.216 Å))

____________________________________________________X X –– ray diffraction patternray diffraction pattern

Bragg condition:Bragg condition:

nnλλ = 2dsin= 2dsinθθ

20 30 40 50 60

x=0.3

x=0.25

x=0.2

x=0.15

x=0.1

x=0.05

x=0

(312

)

(114

)(1

31)

(040

)(2

20)

(202

)(0

22)

(021

)

(112

)

(111

)

(110

)

Inte

nsity

(a.u

.)dd

____________________________________________________Phase diagrams of R1-xAxMnO3

degrees of freedom: charge, spin, orbital

What’s the new physics

____________________________________________________

3. Physical properties & mechanism

SP

O-2 t2g

eg

Mn+4: 3d3 (t2g3 eg0)Mn+3: 3d4 (t2g3 eg1)

t2g

ege- h+

____________________________________________________Double exchange (1951, Zener)

(La,Sr,)MnO3

Mechanism vs. degree of freedomMechanism vs. degree of freedom_______________________________________________________________________________________________

_

♣ FM/AFM superexchange♣ Charge/orbital ordering♣ double exchange♣ Lattice distortion

(John-Teller effect)

--- spin--- charge/orbital--- charge/spin--- lattice

Physical Review B, Volume 58, Number 17 1 November 1998-I Phase diagram of manganese oxide

Ryo Maezono, Surnio Ishihara, and Naoto NagaosaDepartment of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan

__________________________________________________________________________________________

SonHundK HHHHH +++= site

ddtH jiij

ijK ')('

'σγσγ

σγγ

γγ +∑=

∑ ⋅−=i

ieitHHund gg SSJH 2

)~~( 2i

2site on iei gSTH αβ +−= ∑

jtij

itSS gg SSJH 22)(

⋅= ∑

(Kinetic energy of eg electrons)

(Hund coupling between eg & t2g spins)

(Coulomb interaction between eg-electrons)

(Super exchange t2g spins)

G

2D-F

A

1D-F

Charge Ordering (Mn+4/Mn+3 = n/8)

Chen et al., J. Appl. Phys. 81 (1997)

(0.67~5/8)

(0.5=4/8)

Mn+3 Mn+4 Mn+4 Mn+3

Spin/orbital structure

Neutron diffractionNeutron diffractionMagnetic Magnetic DichroismDichroism

Nd1-xSrxMnO3

Kajimoto et al., PRB 30, 9506 (1999)

Tobe, PRB 67, 140402 (2003)

Orbital switching in A-type spin state

Spin A-Type :

from d3z2-r2 to dx2-y2

at TN ~ 220 K

Spin C-type :

remains d3z2-r2

with TN ~ 270 K

FMFM AFMAFM

Origin of CMR: Phase separationOrigin of CMR: Phase separation

M. Uehara, et all, Nature 399 (1999)M. Uehara, et all, Nature 399 (1999)

Metallic ClusterMetallic Cluster

AFM Melting as HAFM Melting as H≧≧1 Tesla (insulator)1 Tesla (insulator)

Spin line up (metal)Spin line up (metal)

4-a. Experiment --- bulk

Phase separation--- fine tuning the MR value by

Ionic radius size

____________________________________________________

Key parametersKey parameters_______________________________________________________________________________________________

_

• hole concentration(charge/orbital/spin)

• radius of A-site(lattice/ spin)

Mn3+ Mn4+

Mn3+

O2-

Mn4+

____________________________________________________Bulk MakingBulk Making

Step 1 Pre-heating R2O3: 900℃/ 3 h .

Step 2 Mix R2O3 ,CaCO3, SrCO3, MnCO3

Step 3 Reaction: 1200℃/ 24 h

Step 4 Pellet :d = 1 cm, Thickness =3 mm, 3 tons/ cm-2

Step 5 Anneal: 1400℃ /16 h

⇒⇒

____________________________________________________

0 – 7 Tesla1.4 – 400 KHall effectresisitivityAC susceptibility

Physical Property measurement System (PPMS)

T (K)T (K)M

(M

( em

uem

u ))

____________________________________________________Basic M Basic M –– T curveT curve

ParaPara-- to to antiferromagneticantiferromagnetic

TTcc

ParaPara-- to ferromagneticto ferromagneticM

(M

( em

uem

u ))

T (K)T (K)

TTNN

M ~ C/T , C/(T+TM ~ C/T , C/(T+TN N ), C/(T), C/(T--TcTc) )

T (K)T (K)

ρρ(o

hm(o

hm-- c

m)

cm)

T (K)T (K)ρρ

(ohm

(ohm

-- cm

)cm

)

____________________________________________________Basic R Basic R –– T curveT curve

metalmetal insulatorinsulator

ρρ = = ρρoo ++ρρ11TTαα ρρ = = ρρoo exp(C/Texp(C/Tββ))

PHYSICAL REVIEW B, VOLUME 65, 024422 (2001)Thermal and magnetic instability near the percolation threshold of

Nd0.5Ca0.5-ySryMnO3C. W. Chang,* A. K. Debnath,† and J. G. Lin‡

Center for Condensed Matter Science, National Taiwan University, Taipei, Taiwan

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0

0

4

8

1 2

1 6

y = 0 .1

8 th ru n

1 s t ru n

ρ (o

hm-c

m)

T (K )

0

2

4

6

y = 0 .0 9

8 th ru n

1 s t ru n




0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0

0

4

8

1 2

1 6

y = 0 .1

8 th ru n

1 s t ru n

ρ (o

hm-c

m)

T (K )

0

2

4

6

y = 0 .0 9

8 th ru n

1 s t ru n

0 50 100 150 200 250 300

0.0

0.2

0.4

0.6

H = 100Oe

T (K)

0.0

0.1

0.2

0.3

0.4

H = 100Oe

y = 0.08

y = 0.1

25 50 75 100 125102

103

104

105

106

y = 0.08 1st 2nd 3rd 4th 5th 6th

ρ (o

hm-c

m)

T (K)

0 50 100 150 200 250 30010 -110 010 110 210 310 410 510 6

y = 0 .08

H = 0

H = 0 .5T

H = 1 .3Tρ (o

hm-c

m)

T (K )

PHYSICAL REVIEW B, VOLUME 65, 024422 (2001)Termal and magnetic instability near the percolation threshold of






0 50 100 150 200101

102

103

104

105

106

107

108170K

150K

130K120K100K65K11K

ρ (o

hm-c

m)

T (K)

1. 3 Tesla1. 3 Tesla




1 10 100 1000

0

20

40

60

80

100

120

A

T (K)

50K

11K150K

130K80K

120K

100K

110K

Δρ/

ρ (%

)

Time (min)

0 100 200 300

Δρ/ρ = Α lnt+const.

J OF APPLIED PHYSICS VOLUME 90 (2001)Enhancement of magnetoresistance in the intermediate state

of Pr0.5Sr0.3Ca0.2MnO3C. W. Chang and J. G. Lin

Center for Condensed Matter Science, National Taiwan University, Taipei, Taiwan 10764

FIG. 2. I –V curves for Pr0.5Sr0.3Ca0.2MnO3 at 120, 100, and 80 K, respectively.The arrows denote the jumps of voltage. The inset shows the temperaturedependence of the onset voltage of the jump with the forward scan(increasing ) and the backward scan (decreasing).




FIG. 2. I –V curves for Pr0.5Sr0.3Ca0.2MnO3 at 120, 100, and 80 K, respectively.The arrows denote the jumps of voltage. The inset shows the temperaturedependence of the onset voltage of the jump with the forward scan(increasing ) and the backward scan (decreasing).

4-b. Experiment : films & bilayers

____________________________________________________

Subject (1): Nanocrystalline LSMO films--- High electroresistance

& low field MR effects

____________________________________________________

Experiment Flow ChartExperiment Flow Chart

Target preparation (Solid State ReactionSolid State Reaction)

Structure Analysis (XRDXRD)

Resistance

MorphologyMagnetism

Composition

EDSEDS

PPMS & SQUIDPPMS & SQUID

PPMSPPMS TEMTEM

Thin Film Deposition (Sputtering,PLDPLD)

Thin Film Charaterization

Nd0.7Ca0.3MnO3 (NCMO):

Nd2O3, CaCO3, MnCO3 Powder100°C (3 hrs.) in air 1100°C (24 hrs.) in air

YBaYBa22CuCu33OO77 (YBCO)

Y2O3, BaCO3, CuO2 Powder100°C (3 hrs.) in air 1050°C (36 hrs.) in oxygen400°C (12 hrs.) in oxygen

____________________________________________________

Solid state reaction

Target preparationTarget preparation

Powders

____________________________________________________RF sputter system (Millton CVT, 13.6 MHz)

10-8 torrfour guns1000 °C

Ar

LaAlO3 substrate

Reactive co-sputtering process

O2

LSMOYBCO

Film making

• Substrate ⇒ Si (100) , LaAlO3(100)

• Target ⇒

• Base pressure ⇒ 3 × 10-7 torr

• Mixed gas ⇒ Ar:O2=98:2

• Sputtering pressure 70 mtorr

• Base temperature ⇒ Room temperature

• pre-sputtering ⇒ 3 minutes

• Working distance ⇒ 10 cm

• Annealing tempert.

Annealing time ⇒

800 – 920 ℃ (700 ℃)

• 1 hrs

• RF power ⇒ 80 Watt

YBCO, LSMO

NonNon--uniform strain in Launiform strain in La0.670.67CaCa0.330.33MnOMnO33 filmfilm

InterfaceLow strainHigh strain

PRB 61, 9665 (2000)

____________________________________________________

Lattice parameter a

LCMO=3.86Å

NGO(110)=3.86 Å (no strain)

LAO(100)=3.79 Å (Compressive)

STO(100)=3.91 Å (Tensile)

AFM - granular

50 -100 nm

Rrms = 3 nm

____________________________________________________20 30 40 50 60 70

2θ

*LaAlO3

(001

)*

(002

)*

(002

)

Structures of LSMO layer

XRD – monoclinic

c-oriented

20nm

H=500 Gauss

ZFC(black line); FC (red line)

10nm0 50 100 150 200 250 300

40

60

80

100

120

140

160

180

200

220

240

260

M (

emu

/cm

3 )

T (K)

30nm

0 50 100 150 200 250 300

60

80

100

120

140

160

180

200

220

M (e

mu

/ cm

3 )

T (K)

0 50 100 150 200 250 300

0

20

40

60

80

100

120

140

160

180

200

M (

emu

/ cm

3 )

T (K)

0 50 100 150 200 250 300

-40

-20

0

20

40

60

80

100

120

140

160

M (

emu

/ cm

3 )

T (K)

?

0 50 100 150 200 250 30060

80

100

120

140

160

180

200

220

240

M (

emu

/cm

3 )

T (K)

40nm 50nm

0 50 100 150 200 250 30060

80

100

120

140

160

180

200

220

240

M (

emu

/cm

3 )T(K)

60nm

____________________________________________________Magnetization for LSMO

10 nm10 nm

0 50 100 150 200 250 300 3500.05

0.10

0.15

0.20(C)

T (K)

-MR

(%)

ρ (Ω

-cm

)

T(K)

0 100 200 3004

8

12

16

0.08

0.16 (b)

-MR

(%)

T (K)0 100 200 300

5

10

15

20

0.4

0.6

0.8(a)

-MR

(%)

T (K)

H = 0 H = 1T

0 100 200 300

6121824

60 nm

80 nm

100 nm

PHYSICAL REVIEW B 67, 064412 (2003)Current-induced giant electroresistance in La0.7Sr0.3MnO3 thin films

A. K. Debnath* and J. G. Lin†Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan

-8000 -4000 0 4000 8000-4

-3

-2

-1

03.85%(c)

ΔR/R

o (%

)

H (Oe )

-4

-3

-2

-1

0 2.85%(b)

-4

-3

-2

-1

0 2.96%(a)

-0.4 -0.2 0.0 0.2 0.430

31

32

33

-ER

(%)

I (mA)

(c)

dV/d

I (K

Ω)

I (mA)

22

24

26

-ER

(%)

I (mA)

(b)

108

112

116

120

124

-ER

(%)

I (mA)

(a)

0.0 0.1 0.2 0.3 0.40246

0.0 0.2 0.4 0.6 0.8 1.00

2

4

6

0.0 0.2 0.4 0.6 0.8 1.00369

12

PHYSICAL REVIEW B 67, 064412 (2003)Current-induced giant electroresistance in La0.7Sr0.3MnO3 thin films

A. K. Debnath* and J. G. Lin†Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan

thickness (nm) MRH (%) MRI (%) ratio

60 2.96 5.6 (I = 0.3) 1.9

80 2.85 6.4 (I = 0.3) 2.311.3 (I = 0.9) 4.0

100 3.85 3.5 (I = 0.3) 0.94.6 (I = 0.9) 1.2

_______________________________________________________________________

Current in Current in nanowirenanowire of LSMO inducedof LSMO inducedmagnetic field, and the thermalmagnetic field, and the thermalenergy delocalized the electrons.energy delocalized the electrons.

PHYSICAL REVIEW B 67, 064412 (2003)

Current-induced giant electroresistance in La0.7Sr0.3MnO3 thin filmsA. K. Debnath* and J. G. Lin†

Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan

Subject (2): Nanocrystalline YBCO/LSMObilayers

--- Proximity effect, spin injection& vortex pinning

____________________________________________________

____________________________________________________Multilayer devices

YBCO

LSMOYBCO

YBCO

YBCO

LSMO

LSMO

LSMO

V IV

IinjectVI

I

Spin-injectionIc - depression

proximity effectTc - depression

FM/N/FM structureMR enhancement

____________________________________________________Interesting topics on YBCO/LSMO

1) Proximity effects 2) Andreev reflection3) Spin injection4) Spin-accumulation5) π –phase shift

Superconductor

Ferromagnet

Cooper pair

FM spin

____________________________________________________Proximity effect

1) Influence of magnetism on supercond.

Intermixing ⇒ effective exchange field

Heffect = Hex [dF/(ds+dF)], Tc oscillation

2) Influence of supercond. on magnetism

Intermixing ⇒ reconstruction of magnetic order

Tcurie oscillation

____________________________________________________

●● Normal electron injected to Normal electron injected to superconductor will besuperconductor will bereflected as a hole;reflected as a hole;

●● Polarized electron injectedPolarized electron injectedinto superconductor will kill into superconductor will kill a Cooper pair.a Cooper pair.

Spin-injection

____________________________________________________

●● YBaYBa22CuCu33OO77 ξS ~ 3-10 nm●● Critical parameter Tc = 90 K, Hc2 ~ 165 T ●● SQUID, Bolometer, Filter, ResonatorSQUID, Bolometer, Filter, Resonator……

SuperconductorSuperconductor: : RRBaBa22CuCu33OO77, R = Y or rare earth element, R = Y or rare earth element

Ba

Y

Ba

a=3.89Å

c=11.7Å

Wu, Chu et al., PRL (1987)

Half metal: (RHalf metal: (R,,Ca)MnOCa)MnO33, R = La, , R = La, NdNd, Pr, Pr……..

c R,Ca

R, Ca

Mn+3

b

a

___________________________________________________

●● Ferromagnetic with 90 % polarizationFerromagnetic with 90 % polarizationfor LCMO. for LCMO. ξξMM ~ 10 -15 nm

●● Colossal Colossal magnetoresistancemagnetoresistance (CMR)(CMR)●● Sensor, pickSensor, pick--up head, MRAMup head, MRAM

Jin et al, Science (1995)

dd--bandband

SS--bandband

____________________________________________________

LCMO = 15 unit cell ~ 10 nmLCMO = 15 unit cell ~ 10 nmN = unit cell of YBCON = unit cell of YBCON = 3 to 12N = 3 to 12

~ 3.5 to 14 nm~ 3.5 to 14 nmΔΔTcTc ~ 62 to 2 K~ 62 to 2 K

EEeffeff--exex ~ 0.74 to 0.42 of ~ 0.74 to 0.42 of EEexexN = 12N = 12

N = 1N = 1

____________________________________________________Vortex pining device

YBCO

LSMO

V

I

____________________________________________________

Critical current ICNormal state resistance RnEnergy gap Δ

Ic = I(V=1 μV) IC Rn = π ∆ / 2

= 3.52 π KB TC / 4

I-V characteristic

-4 -2 0 2 4-0.9

-0.6

-0.3

0.0

0.3

0.6

0.940nm

30nm20nm

10nm

YBCO

V (v

olt)

I (mA)

____________________________________________________I- V Characteristic (1.9 K)

Ic decreases with increasing thicknessof LSMO

____________________________________________________Hysteresis in YBCO/LSMO(30nm)Hysteresis in YBCO/LSMO(30nm)

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

-0.04

-0.02

0.00

0.02

0.04

2T

5T

3T4T

1T0T

V (v

olt.)

I (mA)

YBCOYBCO

Subject (3): Epitaxial YBCO/NCMObilayers

--- How the superconductivity is affected by weak ferromagnetic insulator ?

____________________________________________________

La1-xSrxMnO3

E. Dagotto et. al., Physics Reports 344, 1-153 (2001)

____________________________________________________

R0.7(Ca,Sr)0.3MnO3

C. N. R. Rao et al. J. Phys. Chem. Solids 59, 487 (1998)

____________________________________________________Substrate criteriaSubstrate criteria

1. Atomically flat2. Chemically comparable3. Well lattice mismatch

For YBCO, LaAlO3 (100) is ~ 0.4%;SrTiO3(100) is 0.2% for a-parameter, 0.3% for b-parameter; NdGaO3 (110) is 0.7 % for a- and b-parameters

YBa2Cu3O7 (001), orthorhombic

LaAlO3 (100), rhombohedra

LaAlO3a=b=c=3.79 Åα=β=γ=90.12o

o-YBa2Cu3O7a=3.82 Å, b=3.85 Å, c=11.63 Å; α=β=γ=90o

3.79Å

3.79Å

b

a

c

Nd0.7Ca0.3MnO3 (001), orthorhombic

5.42Å

5.46Å5.44Å

5.44Å

o-Nd0.7Ca0.3MnO3a=5.42 Å, b=5.46 Å, c=7.72 Å;α=β=γ=90o

PulsePulse--LaserLaser--Deposition system Deposition system ––NeoceraNeocera 180180

Chamber

10-8 torr

PumpFlow meterVacuum gauge

KrF Laser (248 nm) Focus Len

PulsePulse--Laser Deposition system (II) Laser Deposition system (II) -- ChamberChamber

YBCO

NCMO

NCMO/YBCO NCMO/YBCO heterostructureheterostructure

Nd0.7Ca0.3MnO3, (40 -350 nm)

780oC for 1 hour in 50 mtorr O2

LaAlO3 (100)

YBa2Cu3O7(100-600 nm)

850 oC for 1 hour

400 °C for 6 hours

in 300 mtorr O2

____________________________________________________

____________________________________________________

10 20 30 40 50 600

2

4

10 20 30 40 50 600

4

8

2θ

NCMO(004)NCMO

(002)

YBCO(004)

YBCO(003)

YBCO(006)

YBCO(007)

YBCO(005)

LAO

YBCO(002)

(b)

Inte

nsity

(abi

tary

)

LAO(a)

X-ray Diffraction Patterns & TEM image

●● Both NCMO & YBCOare with c-axis perpendicularto the film surface

2nm001

LAONCMO

●● Epitaxial growth along [001]

____________________________________________________Basic characterizationBasic characterization

(Scanning EDX)

____________________________________________________Magnetization(MMagnetization(M) vs. Temperature (T) ) vs. Temperature (T) –– by SQUIDby SQUID

100 200

-0.4

0.0

0.4

50 1000

50

100

M (

10-6em

u)

T(K)

ZFC FC

NCMO

80 85 90 95 100

-50

0

50

ZFC FC

M(1

0-6em

u)

T(K)

YBCO

M(1

0-3 e

mu)

T(K)

ZFC FC

(a)

(b)

●● Tc is 88 K for YBCO; TN is ~ 75 K for NCMO; Both transition temperature do not change in NCMO(40nm)/YBCO(160nm).

____________________________________________________

0 50 100 150 200 250 3000.0

0.1

0.2

0.3

0.4

0.5

0.0

5.0x103

1.0x104

1.5x104

2.0x104

ρ (m

ohm

-cm

)

T(K)

YBCO

NCMOTcon

Tcoff

V

LAO

NCMO

I

●● YBCO : Tc ~ 88 K & ΔT < 2 K; NCMO: Insulating

44--Probe methodProbe method

____________________________________________________●● For Ia = 1 – 90 mA, normal state increases & Tc drops

with a rate 0.1K/mA.●● open a gap at 230 K ?open a gap at 230 K ?

Resistivity (ρ) vs. Temperature (T)

YBCO(200nm)

50 100 150 200 2500.0

0.2

0.4

0.6

80 85 900.0

0.1

0.2

0.3

ρ (1

0-3oh

m-c

m)

T(K)

0.1mA 10 mA 30 mA 50 mA 70 mA 90 mA

ρ (1

0-3 o

hm-c

m)

T(K)

____________________________________________________

●● For Ia = 5 – 30 mA, resistivity decreases.


NCMO(200nm)

100 150 200 250

100

101

102

103

104

200 250

10-1

5 mA 10 mA 20 mA 30 mA

ρ (o

hm-c

m)

T(K)

0.0001mA 0.001mA 0.01mA 0.1mA 1mA

ρ (o

hm-c

m)

T(K)

____________________________________________________

0 50 100 150 200 2500.0

0.5

1.0

1.5

40mA

1mA

ρ (m

ohm

-cm

)

T(K)

1mA

40mA

●● For Ia = 1 – 40 mA, normalstate increases & Tc dropswith a rate of 1.0 K/mA.


NCMO(200nm)/YBCO(200nm)

10 20 30 40 50 60 70 800

2

4

6

8

10

R (o

hm)

T(K)

1 mA

40mA

30mA

20mA

10

Crossing point

____________________________________________________

●● For Ia = 1 – 40 mA, normalstate decreases 30% & Tc drops with a rate of 1.4 K/mA.


NCMO(40nm)/YBCO(160nm)

0 50 100 150 200 2500

5

10

15

0.001mA 0.01mA 0.1mA 1mA

ρ (1

0-3 o

hm-c

m)

T(K)

40mA30mA 20mA

10mA

10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

140 0.001mA 0.01mA 0.1mA 1mA

R(o

hm)

T(K)

40mA30mA

20mA10mA

____________________________________________________

●● Tc is suppressed by proximityin NCMO/YBCO at I < 1 mA.

●● Tc-suppresion rate at I > 1 mAis one order higher in bilayerdue to the spin-injection.

Superconducting temperature vs. applying current

0 20 40 60 80 100

10

20

30

40

50

60

70

80

90

T c (K

)

I (mA)

YBCO

NCMO(40)/YBCO(160)

NCMO(200)/YBCO(200)

____________________________________________________

●● Current induces spin-injection effect

Observe a threshold of effective current I > 1 mALarge Tc-suppresion in a rate of 1.4 K/mA.

●● Proximity effect

Heff-ex = Hex {dF/(dS + dF)}

0.5Hex for NCMO(200nm)/YBCO(200nm)0.2Hex for NCMO(40nm)/YBCO(160nm)

ΔTc ~ 34K / 16K

Half metal is the future material forall kinds of spintronic devices !!!

____________________________________________________

Spintronics --- Half metal Colossal Magnetoresistancespin/course/97/20080501.pdf · Spintronics --- Half metal and Colossal Magnetoresistance Jauyn Grace Lin Cener for Condensed Matter

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