____________________________________________________

Proximity and vortex pinning in YBCO/LSMO bilayers

Jauyn Grace Lin

Cener for Condensed Matter sciencesNano-storage Research Center

National Taiwan Univsersity

Phys. Dept. NTHU. 2005/10/4

Miss Su-Ling Cheng (鄭淑齡)Center for Condensed Matter Sciences, N T U

Prof. C. R. Chang (張慶瑞)Department of Physics, N T U

Prof. D. Y. Xing (邢定鈺)National Laboratory of Solid State Microstructures& Department of Physics, Nanjing University, China

____________________________________________________Co-workers

____________________________________________________Outline

I. IntroductionHigh-Tc SuperconductorColossal magnetoresistive manganiteProximity and vortex pinning

II. Experiment

III. Results & discussion

IV. Conclusion

____________________________________________________Zero resistance in YBCO

M.K. Wu & C.W..Chu, PRL 58 (1987)

YBa2Cu3O7Tc = 93 KHc2 ~ 165 T

T > Tc : ρ = ρo + AT

T < Tc:ρ = 075 90 105 120 135 150

0

4

8

12

ρ(oh

m-μ

m)

T (K)

TTcc

0 30 60 90 120 150-0.15

-0.12

-0.09

-0.06

-0.03

0.00

Nd

SmGd

Dy

Y

M (e

mu/

g)

Temperature (K)

H=10 Gauss

____________________________________________________Meissner effect in RBCO, R = rare earth ions

NM

SC

T > Tc

T < Tc

____________________________________________________

Vortex structure in type II superconductor

NMNMMixMixMeiMei

____________________________________________________

Vortex pining in type II superconductor

j = 0j = 0

SupercurrentSupercurrentVortex lineVortex line

j (x)j (x)

Bean: Bean: αα = = BjBjcc ------ (1)(1)KK--A: A: αα = = jjcc(B+B(B+Boo) ) ------ (2)(2)

(1)(1)

(2)(2)

____________________________________________________BCS Theory Work?BCS Theory Work?

...

..e-

k1`

k1

q

k2`

k2

Cooper pairCooper pairPhononPhonon--electron interactionelectron interaction

kBTc~ hω exp[-1/g]g = N(0)V

BCS-like kBTc=Echar exp[-(1+λ)/λ]

RVB kBTc=Cδ(t⊥2/t∥2)U (Anderson, 1987)

Hubbard model

kBTc= t∥δexp(-Uδ/ t∥) (Cyrot, 1987)

Charge-transfer/hole-depletion

Tc = Tco－A(n'－no) 2 (Liechtenstein, 1995)

BCS + dx2-y2 symmetry

Tc = [nH(P), Veff(P)] (Chen et al., 2000)

____________________________________________________Models for HighModels for High--TTcc materialsmaterials

____________________________________________________Colossal magnetoresistance (CMR)

1) Very high magnetoresistance(-1500% at 200 K)

2) Polarization 100% (half metal) 3) Metal - Insulator (PM -FM)

transition

S. Jin et al. Science 265 (1994)

SP

O-2 t2g

eg

Mn+4: 3d3 (t2g3 eg

0)Mn+3: 3d4 (t2g3 eg

1)

t2g

eg

e- h+

____________________________________________________Double exchange (1951, Zener)

(La,Sr,)MnO3

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

)~~( 2

i

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

Type MR Field Temp. Material

OMR 0.01% ~Tesla RT Cu,Al

AMR 2 ﹪ 10 Oe RT Fe,Co,Ni

GMR 5~10 ﹪ 2 Oe RT Fe/Cr

CMR 10 (99.9)% 2 T RT(200K) La-Sr-Mn-O

TMR 20 ﹪ 10 Oe RT Co/AlO/Co

____________________________________________________CMR effect toward to CMR effect toward to spintronicspintronic applicationsapplications

c=7.771ÅLa,Sr

La, Sr

La0.7Sr0.3MnO3

Mn+3

b=5.503Å

a=5.471Å

b=3.82Å

Ba

Y

Ba

a=3.89Å

c=11.7Å

YBa2Cu3O7

____________________________________________________Interesting physics in SC/FM

1) Proximity effects2) Magnetic vortex pinning 3) π –phase shift4) Spin injection5) Spin-accumulation6) Andreev reflection

Superconductor

Ferromagnet

SC pair

FM spin

Boundary conditions Boundary conditions →→

____________________________________________________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

____________________________________________________Vortex pining by domain wall

YBCO

LSMO

V

I

aatttt

Attractive force by opposite directional magneticAttractive force by opposite directional magnetic--lines lines

____________________________________________________

RF sputter system (Millton CVT, 13.6 MHz)Base pressure 10-8 torrfour gunsSubstrate temp. 1000 °C

Experimental setExperimental set--up (I)up (I)

____________________________________________________LSMO Target MakingLSMO Target Making

Step 1 Pre-heating La2O3: 900℃/ 3 h .

Step 2 Mix La2O3 , SrCO3, MnCO3

Step 3 Reaction: 1200℃/ 24 h

Step 4 Pellet :d = 5 cm, Thick =1 cm, 3 tons/ cm-2

Step 5 Anneal: 1400℃ /16 h

⇒⇒

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

Post-annealing conditions

Y1Ba2Cu3O7-δ , 150 nm

700oC for 1hour in O2

300oC for 6 hours

LaAlO3

La0.7Sr0.3MnO3

10 to 50 nm

920oC for 1 hour in O2

____________________________________________________

____________________________________________________

• Physical Property Measur. System(Quantum design)7 Tesla, 1.4 – 400 KResisitivity, I-V curveAC/DC susceptibility

• X-Ray Powder Diffractometer(Japan MAC Sience, model MXP18)

• AFM (Solver P47)

Experimental setExperimental set--up (I)up (I)

AFM - granular

50 -150 nm

Rrms = 3 nm

____________________________________________________20 30 40 50 60 70

2θ

*LaAlO3

(001

)*

(002

)*

(002

)

Structures of LSMO layer

XRD – orthorhombic

c-oriented

50nm

H = 500 Gauss

ZFC(black line); FC (red line)

10nm

0 50 100 150 200 250 30040

60

80

100

120

140

160

180

200

220

240

260

T (K)

40 nm

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

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

T (K)

30 nm 20 nm

0 50 100 150 200 250 30060

80

100

120

140

160

180

200

220

240

M (

emu

/cm

3 )

T(K)

60 nm

____________________________________________________Magnetization for LSMO

La0.7Sr0.3MnO3 (LSMO)

-20000 -10000 0 10000 200003100

3150

3200

3250

3300

3350

R (O

hms)

H (Oe)

T=360K, MR=-6.81%

____________________________________________________

-20 0 20 40 60 80 100 120 140 1600

50

100

150

200

250

300

350

400

T p (K

)

dLSMO (nm)

● For tLSMO < 50 nmFerromagnetic insulator

● For tLSMO ≥ 50 nmTM-I = 360 KFerromagnetic metalMR = -6.81% (at room temperature)

Y/L(30nm) Y/L(50nm)

Morphology of YBCO/ LSMO (t)

Pure YBCO

____________________________________________________

20 30 40 50 60 70 80

(020

)

(014

)

(102

)(0

10)

Inte

nsity

(a.u

.)

2θ

*YBCO phase orthorhombic

____________________________________________________Resistivity for YBCO(150nm)/LSMO(t)

0 50 100 150 200 250 3000.00

0.01

0.02

0.03

0.04

0.05

0.06

0nm20nm30nm40nm

50nm

ρ (o

hm-c

m)

T (K)

0 100 200 300 4001E-3

0.01

0.1

1

10

100

10nm 50nm

ρ (o

hm-c

m)

Temperature (K)

LSMO

YBCO/LSMO(t)LSMO(50nm)- FM MetalLSMO(10nm)- FM Insulator

____________________________________________________Ground state of high-Tc superconductor is an insulator ?

Solid lines: without fieldOpen symbols: at 50 tesla

Vanacken et al., PRB 64 (2001)

____________________________________________________Thermoelectric power

120 160 200 240 280

8

12

16

20

24

28

YBCO t = 10nm t = 30nm t = 50nm

S (μ

V/K

)

Temperature (K)

Obertelli et al., PBR 46 (1992)

0.09 < n[Y/L(10-50 nm)] < 0.1 (YBCO)

Our dataOur data

____________________________________________________

-60000 -40000 -20000 0 20000 40000 60000840860880900

T=0.5Tcon, LSMO=10nm

R (O

hms)

H (Oe)(a)

840860880900

20nm

920940960980

10001020

YBCO(150nm)/LSMO/LAO

30nm

(a)

-60000 -40000 -20000 0 20000 40000 6000019400195001960019700198001990020000

R (O

hms)

H (Oe)

282028402860288029002920

385392399406

100nm

50nm

40nm

(b)

R-H curves at mixed state (50K) for Y/L(t) bilayers

++

++

++

++

--

--

____________________________________________________

10 20 30 40 500

1530456075

Tc (K

)

dLSMO (nm)

-10

-5

0

5

10

300K77K

50 K

MR

(%)

Summary of MR in YBCO/LSMO(t) bilayers

R2(YBCO)

R1(YBCO)

R2(YBCO)

R1(LSMO)

____________________________________________________

route 1

route 2

Proposed effective circuit

-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 (2 K)

-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)

YBCO

Ic is defined as the current value where V = 1 µvolt.

Y/Y/L(tL(t))

0 1 2 3 4 5

2M

3M

4M

5M

6M

7M

8M

9M YBCO t =10 nm t = 20 nm t = 30 nm t = 40 nm

J c (A

/cm

2 )

H (T)

Magnetic dependent critical current density____________________________________________________

Jc = Ic/cross-sectionBean: Bean: αα = = BjBjcc

KK--A: A: αα = = jjcc(B+B(B+Boo) )

____________________________________________________Hysteresis in V- I Characteristic

0 1 2 3 4 50.00

0.05

0.10

0.15

0.20

0.25

2 T

3 T

4 T

5 T

1 T

0 T

t = 30 nm

V (m

volt)

I (mA)

● Observing anti-clockwise hysteresis inYBCO/LSMO bilayers

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

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

YBCO (150nm)/LSMO(40nm)at 2 K with 5T field

4

3

2

1

V (V

olts

)

I (mA)

____________________________________________________________________________________________________________________

1.1. Fingerprint of dynamics generated disorder via interaction betweFingerprint of dynamics generated disorder via interaction between fluxen flux--linelinelattice & pinning centers.lattice & pinning centers.

2. A 2. A ““tearingtearing”” of a soft lattice in a narrow regime of (H, T).of a soft lattice in a narrow regime of (H, T).3. A first order 3. A first order depinningdepinning transition.transition.

2H 2H –– NbSeNbSe2 2 single crystalsingle crystal(TTcc = 7.1 K, H= 7.1 K, Hc2c2 ~ 2.3 T)~ 2.3 T)

__________________________________________________________________________________________________________________

2H 2H –– NbSeNbSe2 2 at 4. 7 K, 1 Teslaat 4. 7 K, 1 TeslaTTcc = 7.1 K, H= 7.1 K, Hc2c2 ~ 2.3 T~ 2.3 T

Only fast rate IOnly fast rate I--sweep produces sweep produces HysteresisHysteresis (S = 2(S = 2××101022 A/s)A/s)

When I increases, the flux-line lattice transitsfrom a metastable to a stable state,followed by a dynamic crystallization transition at high currents.

__________________________________________________________________________________________________________________

1. Ag1. Ag--Bi2223 tape at 77 K; fast sweepBi2223 tape at 77 K; fast sweep2. Considering flux creep and 2. Considering flux creep and inhomogenousinhomogenous Flux pinning;Flux pinning;3. Clockwise 3. Clockwise hysteresishysteresis..

♣ Suppression of Tc in YBCO/LSMO(t) bilayer is observed at t = 50 nm, which should be originate from intrinsic proximity effect.proximity effect.

♣ Reversal of the sign of MR ratio in 50-nm YBCO/LSMO

bilayer indicates the competition between

superconductivity and ferromagnetism.

♣ We have observed magnetic pinning effect and

hysteresis in V-I curves of YBCO/LSMO bilayers.

Conclusion____________________________________________________