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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
Phase diagram
new properties of SDW glass
SDW1
Low temperature SDW phase
thermodynamics
dielectric response
Lasjaunias et al. PRL 1994
NMR
Takahashi et al. JPSJ 1986
also AMR, microwave response…
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
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
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
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
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
Frequency dependence at 1.9 K
Cole-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
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(/)(
TB
TB
2
8.3*0
0
0 2 4 6 810
-4
10-3
10-2
10-1
B (T)
,
, d
c
10-10
dc
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!
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)
Ea
ct (
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
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
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
