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I NTERLAYER E XCHANGE C OUPLING , P AIR B REAKING & 2D V ORTEX D YNAMICS IN F ERROMAGNET -S UPERCONDUCTOR H ETEROSTRUCTURES. R. C. B UDHANI Indian Institute of Technology, Kanpur. Collaborator :- K. Senapati Funding :- D.R.D.O. Govt. of India. Objectives :-. - PowerPoint PPT Presentation
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IINTERLAYERNTERLAYER E EXCHANGEXCHANGE C COUPLINGOUPLING, P, PAIRAIR BBREAKINGREAKING & 2D V & 2D VORTEX ORTEX DDYNAMICSYNAMICS ININ
FFERROMAGNETERROMAGNET-S-SUPERCONDUCTORUPERCONDUCTOR HHETEROSTRUCTURESETEROSTRUCTURES
R. C. BUDHANI
Indian Institute of Technology, Kanpur
Collaborator :- K. Senapati
Funding :- D.R.D.O. Govt. of India
Pair-breaking effects of ferromagnetic boundaries in Pair-breaking effects of ferromagnetic boundaries in cuprates.cuprates.
Influence of ferromagnetic boundaries on the vortex Influence of ferromagnetic boundaries on the vortex state of ultra-thin YBCO films.state of ultra-thin YBCO films.
Exchange coupling between two ferromagnets Exchange coupling between two ferromagnets separated by an exotic superconductor.separated by an exotic superconductor.
ObjectivesObjectives :- :-
dFM --- 300 ÅdY --- 50 - 500 Å
dNM --- 100 Å
[100] STO
LSMO
LSMO
YBCO (c-axis)
[100] STO
PBCO
PBCO
YBCO (c-axis)
dNM
dY
dFM
dY
dFM dNM
THIN FILM STRUCTURES
-200 0 200
-2
0
2
(b)
Field (Oe)
H || [110]
M (
10-
4 em
u)
-2
0
2
-200 0 200
(a)H || [100]
50 100 150 200 250 300 3500
1x10-4
2x10-4
M (
emu)
Temperature (K)
with 500 Oe
ZFC FC
LSMO film 600 Å
-: STATE OF MAGNETIZATION IN LSMO:-
Soft Magnetic Films with in-plane Magnetization
MS(T)/MS(0) = 1 - AT3/2
J ~ 2 meV
75 150 225 300 3750
400
800
1100 Å
550Å
450 Å
X= 350Å
LSMO (X) / YBCO (100 Å) / LSMO (X)
Res
ista
nce
(O
hm
s)
Temperature (K)
20 40 60 80 1000
25
50
Res
ista
nce
(Ohm
s)
Temp (K)
50 100 150 200 250 300 350
-8.0
-4.0
0.0
LSMO / YBCO ( X ) / LSMO
ZFC500 Oe
x = 100 Å x = 200 Å x = 300 Å x = 500 Å
M ( 1
0 -4
emu)
Temperature (K)
100
40
60
80
40
60
80
Senapati et al., Phys. Rev. B 70, 174506 (2004)
dY (Å )
Tc (
K)
NM Boundary FM Boundary
0 interfaceC Y C C Y C YtotalT d T T d T d
ln
( )
2 20
4
1 12 2 2
20
2
C C
C Y
C
eff Y C
TT d
zz
d d
0
A
MOST OF THE DYNAMICS SCALES WITH THE EFFECTIVE THICKNESS
interface pair breakingC Y C Y C Ytotal
T d T d T d
Effective Tc due to pair breaking (PB)
Inhomogeneous stress field Hole concentration Reduced Tc
Exchange field Spin injection
Interface transparencyEnhanced PB in a reduced
carrier system
SuperconductingmagnetVacuum canDrive coil
SampleHall sensor
G-10 base
Brass rod
Heating element
-: VORTEX DYNAMICS :-
0.00
0.08
20 40 60 80
4T
|TH
3|
dY = 100 Å / FM boundary[a]
0
121 Hz / 1 Oe
1E-3
10
R (
)
20 40 60 800.0
0.5
1.0 [b]
T (K)
TH'
Irreversibility temperature and field TH3 Inverse sheet inductance (1/L) TH’
TH’ = 1- (4a2/c2d) (1/L) [d = thickness , a = effective radius]
1/L = ln(1/Z)THERMALLY ACTIVETED INVERSE SHEET INDUCTANCE
Senapati et al. Rev. Sci. Instrum. 75, 141 (2004)
0.00 0.02 0.04
-0.4
-0.2
0.0
0.8 1.00
2
4
ln (
T C
(H) /
TC
(0) )
H1/2 / T
C(H) ( T1/2K-1 )
deff
(Å)
H (
T)
T
C(H) / T
C(0)
150 300
30
60
90
Hp
b (
0) (
T)
Tirr Tc(H) Critical temperature at which ac Loss of pinning Loss of phase stiffness
c
c B c
πT HLn =
T 0 4k T (H)
Clean limit pair breaking :
( )0
1/2
0Fk H
k H
1/2c(H)
c(0) c(H)
PB
vh2 = ; = , where l = l 2πH
T Hln T T
slope Pair breaking field H
HPB(0) scales with deff
Two regimes of thermal activation separated by a characteristic temperature T*
0.04 0.08
1
0.1
10.05 0.10 0.15
dY= 75 Å
2 T
0
log
( T
H' )
1/T (K -1)
2 T
10 kHz
21 Hz
log
(T
H')
1 / T ( K -1 )
0.02 0.04
0.1
1
1/T (K -1)
dY= 75 Å
0
4 T
log
( T
H' )
LSMO-YBCO-LSMO
Frequency : 121 Hz
PBCO-YBCO-PBCO
Frequency : 121 Hz
d2P
d0
1/22 2
0
0d
0
d
exp - . nT
, .
n ( ) exp 2
ln
<<
Id f
I C
d
pd
v R
R R R Characteristic length for two dislocation
RT aT
103 104 105
102
104
106
0 250 5000
10
300 / FM 75 / FM 75 / FM 35 / FM
U (
0, H
) (
K )
Field (Oe)
dY(Å)
U0( 1
04 K )
deff
( Å )
High T (> T*) --------- U0(T) Energy of creation of dislocationsLow T (< T*) --------- U0(T) Energy required to move preexisting dislocations
50 100 150
0.05
0.10
0.15
100 200 3000.05
0.10
0.15
J 1 (er
g/cm
2 )
Temperature (K)
75100300
dY(Å)
100 K
20 K
J 1 (er
g/cm
2 )
dY(Å)
Summary
• The dynamics of the vortex state in 2D films of YBCO sandwiched between FM-boundaries has been studied over a wide range of temperature, frequency and magnetic field strength.
• Flux motion is controlled by creation of dislocations near Tm, and by the motion of preexisting dislocations at T<Tm.
•The irreversibility temperature in the vortex state maps onto a clean-limit pair-breaking temperature Tc(H), and the pair-breaking field scales with the thickness of the films.
-1.5
0.0
1.5
-250 0 250
HS
120 K
-250 0 250
-1.5
0.0
1.5
HS
Field (Oe)
100 K
-1.5
0.0
1.5
HS
80 K
-1.5
0.0
1.5
HS
M (
10-4 e
mu)
60 K
-250 0 250-2.5
0.0
2.5
HS
40 K
-250 0 250-4
0
4
HS
20 K
LSMO – YBCO – LSMO(300 Å) – (100 Å) – (300 Å)
M-H curves ; Tc = 62 K
K. Senapati and R. C. Budhani, Submitted to Phys. Rev. B.