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Magnetocapacitive effect in SDW system (TMTSF)2AsF6
D. Starešinić, D. Dominko, K. BiljakovićInstitute of Physics, Zagreb, CroatiaP. Lunkenheimer, A. LoidlInstitute of Physics, University of Augsburg, Germany
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Phase diagram
new properties of SDW glass
SDW1
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Low temperature SDW phase
thermodynamics
dielectric response
Lasjaunias et al. PRL 1994
NMR
Takahashi et al. JPSJ 1986
also AMR, microwave response…
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Multiferroic SDW
SDW: incommensurate AFM + relaxor ferroelectric two coexistent ferroic orders possible multiferroic behaviour
SDW
Nad et al. SSC 1995 Levstik et al. PRB 1998
relaxor ferroelectric
Betouras et al. PRL 2007
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Experiments (TMTSF)2AsF6
very similar to (TMTSF)2PF6
Dielectric measurements in magnetic field T down to 1.9 K B up to 8 T f 20 Hz – 1 MHz
j||a, B||c* Vac=5 mV (instrument limit)
too low for high precision
too high for SDW systems (ET~10 mV/cm) Hemberger et al. Nature 2005
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Resistance
0 0.2 0.4 0.610
2
103
104
105
106
1/T (K)
R (
)
HT
LT
0 2 4 6 810
12
14
16
18
20
22
B (T)
(K
)
HTLT
B=0 T
B=8 T
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Magnetoresistance
MR roughly linear in B T dependence similar to (TMTSF)2PF6
0 2 4 6 80
1
2
3
4
B (T)
(R(B
)-R
(0))
/R(0
)
0 2 4 6 8 10 120
0.1
0.2
0.3
0.4
0.5
T (K)
d(R
(B)/R
(0))
/d(B
)
1.9 K
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1.5 2 2.5 310
6
107
108
T (K)
Re
1.5 2 2.5 3
107
T (K)
Re
Dielectric constant
Similar as in (TMTSF)2PF6
B increases dielectric constant and relaxation time
1.5 2 2.5 310
6
107
108
T (K)R
e
B=0 T B=8 T
300 kHz300 kHz
1.6 kHz
80 Hz
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Frequency dependence at 1.9 KCole-Cole fit
1)(1
)(i
102
103
104
10510
6
107
108
f (Hz)
Re
102
103
104
10510
6
107
f (Hz)
Im
0 T
8 T
0 T
8 T
104
10510
6
107
f (Hz)
Re
B||b’
0 T
5 T
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Parameters at 1.9 K
Littlewood’s pinning&screening theory does not work increases faster than the order parameter B increases domain cooperativity?
)/exp( 00 BB
)/exp( *00 BB
BB dcdc ~)0(/)(
TBTB
28.3
*0
0
0 2 4 6 810
-4
10-3
10-2
10-1
B (T)
,
,
dc
10-10
dc
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Temperature vs field dependence
102
103
104
10510
6
107
108
f (Hz)
Re
102
103
104
10510
6
107
f (Hz)
Im
0 T
8 T
0 T
8 T 102
103
104
10510
6
107
108
f (Hz)
Re
102
103
104
105
106
107
f (Hz)
Im
1.9 K
1.9 K
2.9 K
2.9 K
1.9 K 8 T
Suggests B-T scaling!
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Temperature dependence
0.4 0.45 0.510
6
107
108
1/T (K)
0.4 0.45 0.5
10-5
10-4
10-3
1/T (K)
(s
)
0.4 0.45 0.510
6
107
108
1/T (K)
0.4 0.45 0.5
10-5
10-4
10-3
1/T (K)
(s
)
0 2 4 6 810
15
20
25
30
35
B (T)
Eac
t (K)
0 2 4 6 810
-11
10-10
10-9
10-8
B (T)
0, 0
0 10-13
0
)/exp(0 TEact
0 T
8 T
0 T
8 T
)/exp(0 TEact
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Field dependence
0 2 4 6 810
6
107
108
B (T)
0 2 4 6 8
10-5
10-4
10-3
B (T)
(s
)
0 2 4 6 810
6
107
108
B (T)
0 2 4 6 8
10-5
10-4
10-3
B (T)
(s
)
1.8 2 2.2 2.4 2.62
4
6
8
10
12
T (K)
B0 (T
)
0.4 0.45 0.510
-7
10-6
10-5
10-4
1/T (K)
,
0
010-13
0
Eact=26 K
Eact=13 K
)/exp( 00 BB
1.9 K
1.9 K
)/exp( 00 BB
2.6 K
2.6 K
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Conclusions huge magnetocapacitive effect in
(TMTSF)2AsF6
multiferroic nature of low temperature SDW state
not the consequence of screening no simple relation between the (B¸,T),
(B,T) and (B,T) further measurements with better samples
at lower T, lower f and lower Vac