Magnetic Properties of the New

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Nov 15, 2013 (3 years and 11 months ago)

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H. C. Ku

Department of Physics, National Tsing Hua University,
Hsinchu, Taiwan 300, R.O.C.

with: B. N. Lin, P. C. Guan, Y. C. Lin, T. Y. Chiu, M. F. Tai


Superconductivity and Anomalous
Magnetic Properties of the New
Ru
Ca
2
RCu
2
O
8+


(R = Pr
-
Gd)
System



Introduction

Magnetic Superconductivity in
RuSr
2
RCu
2
O
8+



Ru
-
1212 system (R = Sm, Eu, Gd)


-

tetragonal

TlBa
2
CaCu
2
O
7+


-
type (1212) structure

-

weak ferromagnetic metal
T
m

~ 135 K

-

high
-
T
c

superconductor
T
c

~ 0
-
65 K



*sensitive to oxygen


-

hole concentration


*coexistence with ferromagnetic order (
T
c

< T
m
)



Bauernfeind et al., Physica C 254, 151 (1995)

Bernhard et al., PRB 59, 14099 (1999)


Awana et al., Physica C 357 (2001)

RuSr
2
GdCu
2
O
8+



Tetragonal 1212
-
type

P4/mmm

CuO
5

RuO
6

Gd

Sr

RuSr
2
GdCu
2
O
8+


T
m

= 133 K, T
c

= 16
-
48 K

Bernhard et al.,

PRB 59, 14009 (1999)

R
(T)


v
(T)(ZFC)

S
(T)

M
m
(T)(FC)

Normal or abnormal

ferromagnetic magnetic
hysteresis curve M(B
a
)

for T < T
m

= 135 K?

-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-12
-9
-6
-3
0
3
6
9
12
0.83


/f.u.
T
c
< 100 K < T
C
10 K < T
c
?


Magnetization M
m
(10
3
emu/mol)
Applied field B
a
(T)
RuSr
2
GdCu
2
O
8+

Current oxygen
-
deficient sample

superconducting T
c

~ 10 K

superconducting signal?

Bernhard et al.,

PRB 59, 14009 (1999)

ZFC/FC susceptibility

Superconducting diamagnetic signal?

0
50
100
150
200
-2
0
2
4
6
8
10
12
T
c
T
m
= 135 K
1-G ZFC
100-G ZFC
100-G FC
1-G FC
RuSr
2
GdCu
2
O
8+

oxygen-deficient


Susceptibility

m
(cm
3
/mol)
Temperature T (K)
Current oxygen
-
deficient sample

superconducting T
c

~ 10 K

superconducting signal?

Cordero et al., PRB 67, 144519 (2003)

Superconducting diamagnetic signal appears only in

very low applied fields due to strong ferromagnetic
background

M
g
(T)(FC)

Papageorgiou & Braun,

PRB 66, 104509 (2002)

1.14
1.12
1.10
1.08
1.06
1.04
1.02
0
10
20
30
40
50
60
70
80
Pr
Nd
Sm
Eu
Gd
Gd
Gd
Eu
Gd
Gd
Gd
Gd
Sm
Eu
Gd
Eu
Eu
Eu
Tb
Dy
Y
no T
c
(01)
65 K (03)
no T
c
(01)
33 K (99)
48 K (99)
12 K (01)
T
m
~135 K
Ru-1212 (P4/mmm)
RuSr
2
RCu
2
O
8+



Superconducting T
c
(K)
rare earth ionic radius R
3+
(
Å
)
T
c

only in R = Sm, Eu, Gd of RuSr
2
RCu
2
O
8+


With oxygen effect
-

hole concentration



What about the
RuCa
2
RCu
2
O
8+


system


(R = La, Ce, Pr, Nd, Sm, Eu, Gd)?



First try R = Pr

: RuCa
2
PrCu
2
O
8+




Question

Results and Discussion



RuCa
2
PrCu
2
O
8+





RuCa
2
-
x
Sr
x
PrCu
2
O
8+


system (2


x


0
)



RuCa
2
RCu
2
O
8+


system


(R = La, Ce, Pr, Nd, Sm, Eu, Gd)




Sample preparation:


Direct one
-
step, oxygen annealed


5
10
15
20
25
30
35
40
45
50
55
60
65
70
0
500
1000
1500
2000
Orthorhombic (Pmmm?)
a
= 5.874
Å
b
= 5.785
Å
c
= 22.460
Å
(1014)
(1111)
(225)
(216)
(118)
(115)
(004)
(103)
(410)
(320)
(1013)
(314)
(223)
(220)
(117)
(107)(008)
RuCa
2
PrCu
2
O
8+





Intensity (arb. unit)
2

(degree)
Distorted
orthorhombic

variation of tetragonal 1212


structure:
a
o

~
b
o

~

2
a
t


c
o

~ 2
c
t

0
10
20
30
40
50
60
-10
-8
-6
-4
-2
0
2
4
T
c
T
m
1. Annealed in O
2
12 h (D day)
2. Bulk sample, 100 G
3. Measured at D+2 and D+10 days
ZFC (D+10)
FC (D+10)
FC (D+2)
ZFC (D+2)
RuCa
2
PrCu
2
O
8+



Susceptiblity

m
(cm
3
/mol)
Temperature T(K)
Abnormal low temperature magnetic behavior


at different measuring times
oxygen diffusion effect

Normal

ZFC/FC susceptibility and magnetic hysteresis
for standard high
-
T
c

superconductors without
magnetic order

0
10
20
30
40
50
60
-1.6
-1.2
-0.8
-0.4
0.0
0.4
T
c
= 37 K
ZFC
FC
B
a
= 100 G
La
1.85
Sr
0.15
CuO
4


Susceptibility

m
(cm
3
/mol)
Temperature T (K)
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-12
-9
-6
-3
0
3
6
9
12
T = 10 K < T
c
La
1.85
Sr
0.15
CuO
4+



Magnitization M
m
(10
2
emu/mol)
Applied field B
a
(T)
Magnetization M
m
(T) in different applied fields

Anomalous FC/ZFC behavior

0
10
20
30
40
50
60
-8
-6
-4
-2
0
2
4
1-G/FC
T
c
T
m
1,10 &100-G/ZFC
1-kG/ZFC
1-kG/FC
10-G/FC
100-G/FC
RuCa
2
PrCu
2
O
8+


Magnetization M
m
(10
2
emu/mol)
Temperature T (K)
Normal paramagnetic behavior for T > T
m

&

Mgnetic order (weak
-
ferromagnetic or spin
-
glass?)


for T
m

> T > T
c

-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.16

B
/f.u.
40 K ~ T
c
(WFM + S?)
T = 60 K > T
m
(paramagnetic)
45 K < T
m
(weak ferromagnetic?)
RuCa
2
PrCu
2
O
8+



Magnitization M
m
(10
2
emu/mol)
Applied field B
a
(T)
Weak

magnetization relaxation at T= 45 K < T
m

(
itinerant weak ferromagnetism almost spin
-
glass
-
like
)


0
50
100
150
200
ZFC to 45 K
T = 45 K < T
m
~ 50 K
10
4
10
3
10
2
"0 G"
45 K
WFM
1 kG, 100 K
1 kG (FC), 45 K
1 kG (ZFC), 45 K
RuCa
2
PrCu
2
O
8+



Magnetization M
m
(emu/mol)
Time t (s)

Spin
-
glass
-
like weak hysteresis m(B
a
) and relaxation m(t)

for paramagnetic Ca
1
-
x
Sr
x
RuO
3

x = 0 & 0.2

Lin et al., JMMM, in press (2004)

-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-8
-6
-4
-2
0
2
4
6
8
0.03

B
0.07

B
x = 0
x = 0.2
Ca
1-x
Sr
x
RuO
3
T = 5 K
Magnetization m (x10
-2


B
/f.u.)
Applied field B
a
(T)


10
2
10
3
10
4
0.0
0.5
1.0
1.5
0 G
5 K
1 kG (FC)
5 K
1 kG, 100 K
1 kG (ZFC), 5 K
ZFC to 5 K
Ca
0.8
Sr
0.2
RuO
3
Magnetization m (x10
-2


B
/Ru)
Time t (s)


EuMnO orthorhombic Pbnm
3
R
Ru
O1
O2
with larger distortion
EuMnO orthorhombic Pbnm
3
R
Ru
O1
O2
with larger distortion
Orthorhombic


(distorted)

Orthorhombic

(pseudo
-
cubic)

a ~ b ~ c/

2

Lattice distortion of CaRuO
3

compared with SrRuO
3

Compare the

magnetic phase diagram of Ca
1
-
x
Sr
x
RuO
3

system with RuA
2
RCu
2
O
8
with the same
RuO
6

configuration

0.0
0.2
0.4
0.6
0.8
1.0
0
50
100
150
200
RuSr
2
GdCu
2
O
8
RuCa
2
PrCu
2
O
8
RuSr
2
PrCu
2
O
8
Ca
1-x
Sr
x
RuO
3
spin glass
x
exchange-enhanced
paramagnetic metal (PM-M)
itinerant ferromagnetic metal
(FM-M)


Curie temperature T
C
(K)
Ru
4/5+

4
d
4

/
d
3


in RuO
6


-

4
d
n


in

t
2g

bands

due to strong
RuO
6

octahedral crystal field splitting
D
cf

and
weak Hund’ rule exchange coupling
J
H

-
strong
Ru 4
d
xy,yz,zx
-
O 2
p
x,y,z

hybridization

-
large on
-
site Coulomb repulsion
U
dd

-
Long
-
range magnetic order


(or short
-
range spin glass)


e
g

t
2g

d

Coulomb
repulsion
U
dd

Charge
transfer
D

On
-
site Coulomb repulsion energy

U
dd

= E(d
n
-
1
) + E(d
n+1
)
-

2E(d
n
)

Charge transfer energy

D

= E(d
n+1
L
)


E(d
n
)

Origin of weak, itinerant ferromagnetic order


-

self
-
doing

with anisotropic
Ru 4
d
xy,yz,zx
-
O 2
p
x,y,z


hybridization

drives the resulting mixed
-
valent


system metallic and ferromagnetic via
double


exchange interaction

-

lower
T
m

~ 50 K

for
RuCa
2
PrCu
2
O
8

as compared with
T
m

~ 135 K

for
RuSr
2
GdCu
2
O
8

(in more robust local
moment regime) indicates weaker double exchange
coupling strength
J
de

due to
RuO
6

distortion



Complex magnetic flux dynamics for T < T
c
< T
m


in magnetization due to interplay between

superconductivity and itinerant ferromagnetic order

-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-10
-8
-6
-4
-2
0
2
4
6
8
10
initial magnetization curve
35 K
T < T
c
(~40 K)
< T
m
(~50 K) (ZFC)
30 K
10 K
RuCa
2
PrCu
2
O
8+



Magnitization M
m
(10
2
emu/mol)
Applied field B
a
(T)
FC and ZFC magnetization at 10 K

show complex interplay
between superconductivity and itinerant ferromagnetic order



-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
(1)
(1)
100-G FC to 10 K
ZFC to 10 K
RuCa
2
PrCu
2
O
8+



Magnitization M
m
(10
2
emu/mol)
Applied field B
a
(T)
Low field (1 G)

time relaxation M(t) at 10 K < T
c
< T
m

-250
-200
-150
-100
-50
0
50
ZFC to 10 K
T = 10 K < T
c
< T
m
10
4
10
3
10
2
"0 G"
10 K
1 G, 100 K > T
m
1 G (FC), 10 K
1 G (ZFC), 10 K
RuCa
2
PrCu
2
O
8+



Magnetization M
m
(emu/mol)
Time t (s)

1
-
G and 1
-
kG

time relaxation M(t) at 10 K < T
c
< T
m

-500
-400
-300
-200
-100
0
100
1 G (FC)
10 K
"0 G"
10 K
"0 G"
10 K
1 G, 100 K
1 G (ZFC), 10 K
10
4
10
3
10
2
1 kG, 100 K
1 kG (FC)
10 K
1 kG (ZFC), 10 K
ZFC to 10 K
RuCa
2
PrCu
2
O
8+



Magnetization M
m
(emu/mol)
Time t (s)
RuCa
2
PrCu
2
O
8+



-

distorted
orthorhombic

variation of tetragonal 1212


structure:
a
o

~
b
o

~

2
a
t


c
o

~ 2
c
t

-

Ru
4/5+

itinerant weak ferromagnetic metal close to


spin
-
glass
with T
m

~ 50 K

-

superconductor
T
c

~ 37
-
40 K


*sensitive to oxygen


--

hole concentration),


*coexistence with weak magnetic order


-

anomalous ZFC (Meissner) & FC (field expulsion)


behavior due to interplay with ferromagnetic order



Powder x
-
ray diffraction patterns of

tetragonal RuSr
2
PrCu
2
O
8+



5
10
15
20
25
30
35
40
45
50
55
60
65
70
0
1000
2000
3000
4000
5000
Tetragonal (P4/mmm)
a
= 3.910
Å
c
= 11.726
Å
x
x
(110)(103)
(102)
(101)
(002)
(220)(206)
(116)(213)
(006)(200)


Intensity (arb. unit)
2

(degree)
PrSr
2
RuCu
2
O
8+

5
10
15
20
25
30
35
40
45
50
55
60
65
70
Intensity (arb. unit)
2

(degree)
1.0
2.0
0.8
0.6
0.2
0
0
0
0
0
0
Ru Ca
2-x
Sr
x
PrCu
2
O
8
+


x = 0
Powder x
-
ray diffraction patterns
for RuCa
2
-
x
Sr
x
PrCu
2
O
8+


Low temperature spin
-
glass
-
like behavior


for tetragonal RuSr
2
PrCu
2
O
8+


Ref: Awana et al. Physica C357
-
360, 121 (2001).

0
10
20
30
40
50
60
3
4
5
6
7
8
RuSr
2
PrCu
2
O
8+

T
merge
(1 T)
exchange-enhanced
paramagnetism
spin glass
FC
ZFC
1-T
1-kG
100-G


Susceptibility

m
(10
-2
cm
3
/mol)
Temperature T (K)
Low temperature spin
-
glass
-
like behavior


for tetragonal RuSr
2
PrCu
2
O
8+


-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-6
-4
-2
0
2
4
6
0.12


/f.u.
T = 10 K
spin glass?
T = 20 K
paramagnetic
RuSr
2
PrCu
2
O
8+



Magnitization M
m
(10
2
emu/mol)
Applied field B
a
(T)
0
10
20
30
40
50
60
70
T = 10 K < T
merge
~ 17 K
spin glass
"0 G"
10 K
small
1 kG, 100 K
1 kG (FC), 10 K
1 kG (ZFC), 10 K
ZFC to 10 K
10
4
10
3
10
2
RuSr
2
PrCu
2
O
8+



Magnetization M
m
(emu/mol)
Time t (s)
Weak

magnetization relaxation at T= 10 K < T
m

spin
-
glass
-
like

for tetragonal RuSr
2
PrCu
2
O
8+


Field
-
cooled (FC) susceptibility
for RuCa
2
-
x
Sr
x
PrCu
2
O
8+


0
10
20
30
40
50
60
-8
-6
-4
-2
0
2
4
x = 0.0
100 G FC
RuCa
2-x
Sr
x
PrCu
2
O
8
+

x = 0.1
x = 0.2
x = 0.6
x = 1.0


Susceptibility

m
(cm
3
/mol)
Temperature T (K)
x = 2.0
0
10
20
30
40
50
60
-8
-6
-4
-2
0
2
4
x = 0.1 ZFC
B
a
= 100 G
x = 0 ZFC
x = 0.1 FC
x = 0 FC
RuCa
2-x
Sr
x
PrCu
2
O
8
+



Susceptibility

m
(cm
3
/mol)
Temperature T (K)
Magnetic behavior
for RuCa
2
-
x
Sr
x
PrCu
2
O
8+

(x = 0, 0.1)

RuCa
2
-
x
Sr
x
PrCu
2
O
8+


system


-

orthorhombic

1212 structure only near
RuCa
2
PrCu
2
O
8+




(
x ~ 0)

-

multiphase samples for 0 < x < 2

-

diamagnetic, superconducting signal

observed only


for x


0.2

-

spin
-
glass
-
like behavior

for tetragonal
RuSr
2
PrCu
2
O
8+




(
x = 2)






5
10
15
20
25
30
35
40
45
50
55
60
65
70
(124)
(320)
(030)
(221)
(118)
(017)
(117)
(115)
(103)
(004)
R = Pr
R = Gd
0
0
RuCa
2
RCu
2
O
8+





Intensity (arb. unit)
2

(degree)
Powder x
-
ray diffraction patterns for

RuCa
2
RCu
2
O
8+


(R = Pr, Gd)

0
10
20
30
40
50
60
-8
-6
-4
-2
0
2
4
Pr ZFC
Pr FC
Gd FC
Gd ZFC
B
a
= 100 G
RuCa
2
RCu
2
O
8+



Molar susceptibility

m
(cm
3
/mol)
Temperature T (K)
Magnetic behavior

for RuCa
2
RCu
2
O
8+

(R = Pr, Gd)

5
10
15
20
25
30
35
40
45
50
55
60
65
70
0
0
0
0
0
0
0
Ce
Gd
La
Eu
Sm
Nd
Pr
RuCa
2
RCu
2
O
8+




Intensity (arb. unit)
2

(degree)
Powder x
-
ray diffraction patterns

for RuCa
2
RCu
2
O
8+


0
10
20
30
40
50
60
-15
-10
-5
0
5
10
15
La,Ce
Nd
Pr
Gd
Sm
Eu
100 G FC
RuCa
2
RCu
2
O
8+



Molar susceptibility

m
(cm
3
/mol)
Temperature T (K)
Field
-
cooled (FC) susceptibility

for RuCa
2
-
x
Sr
x
PrCu
2
O
8+



(R = La, Ce, Pr, Nd, Sm, Eu, Gd)

0
10
20
30
40
50
60
0
3
6
9
12
Nd
La, Ce
Eu
Gd
Sm
RuCa
2
RCu
2
O
8+


100 G ZFC


Molar susceptibility

m
(cm
3
/mol)
Temperature T (K)
Zero
-
field
-
cooled (ZFC) susceptibility


for RuCa
2
-
x
Sr
x
PrCu
2
O
8+

(R = La, Ce, Nd, Sm, Eu, Gd)

RuCa
2
RCu
2
O
8+


system


-

orthorhombic

1212 phase in R = Pr, Nd, Sm, Eu, Gd

-

magnetic order
T
m

~ 45
-
50 K

for R = Pr
-
Gd

-

superconductivity
T
c

~ 25
-
40 K

for R = Pr
-
Gd


with
anomalous ZFC and FC behavior due to magnetic


order

-

weak paramagnetic spin
-
glass
-
like behavior signal for


R = La, Ce



Conclusions



Superconductivity

are observed in the


RuCa
2
RCu
2
O
8+d

(R = Pr, Nd, Sm, Eu, Gd)


system with the distorted orthorhombic


1212
-
type structure



Structural and anomalous magnetic


properties

are strongly correlated with the


RuO
6

distortion
and
Ru
4d
-
O
2p

hybridization


with

weak, anisotropic double
-
exchange


coupling strength
due to distortion


Unit for magnetic measurements


Total magnetic moment
m

(
emu
) [
Gaussian system
]

Volume magnetization
M
v

(
emu/cm
3



G
)

Mass magnetization
M
g

(
emu/g = G

cm
3
/g
)

Molar magnetization

M
m

(
emu/mol = G

cm
3
/mol
)

(
M
m



M
g

• molar formula unit weight
)

Magnetic moment per formula unit

m (

B
/f.u.
)

(m


M
m
/(N
o



B
)


Volume magnetic susceptibility

v



M
v
/B
a

(
emu/cm
3
•G = 1
)

Mass magnetic susceptibility

g



M
g
/B
a

(
emu/g

G = cm
3
/g
)

Molar magnetic susceptibility


m

(
emu/mol

G = cm
3
/mol
)


(

m




g

• molar formula unit weight
)

[good for
SI system

with

g



M
g
/

0
B
a
]


0
10
20
30
40
50
60
-10
-8
-6
-4
-2
0
2
4
T
c
(onset)?
1. Annealed in O
2
12 h (D day)
2. B
a
= 100 G at D+2 day
3. B (bulk), P (powder)
4. FC (field-cooled)
ZFC (zero-field-cooled)
T
m
(onset)?
FC(P)
ZFC(P)
FC(B)
ZFC(B)
RuCa
2
PrCu
2
O
8+



Molar susceptibility

m
(cm
3
/mol)
Temperature T (K)
Magnetic behavior

m
(T) for bulk and powder samples

Diamagnetic signal, bulk superconductivity