Magnetocapacitive effect in SDW system (TMTSF) 2 AsF 6 D. Starešinić, D. Dominko, K. Biljaković Institute of Physics, Zagreb, Croatia P. Lunkenheimer, A. Loidl Institute 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 1995Levstik et al. PRB 1998 relaxor ferroelectric Betouras et al. PRL 2007

Experiments (TMTSF) 2 AsF 6  very similar to (TMTSF) 2 PF 6 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 (E T ~10 mV/cm) Hemberger et al. Nature 2005

Resistance  HT  LT B=0 T B=8 T

Magnetoresistance MR roughly linear in B T dependence similar to (TMTSF) 2 PF K

Dielectric constant Similar as in (TMTSF) 2 PF 6 B increases dielectric constant and relaxation time B=0 T B=8 T 300 kHz 1.6 kHz 80 Hz

Frequency dependence at 1.9 K Cole-Cole fit 0 T 8 T 0 T 8 T 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?

Temperature vs field dependence 0 T 8 T 0 T 8 T 1.9 K 2.9 K 1.9 K 8 T Suggests B-T scaling!

Temperature dependence 0 T 8 T 0 T 8 T

Field dependence E act =26 K E act =13 K 1.9 K 2.6 K

Conclusions huge magnetocapacitive effect in (TMTSF) 2 AsF 6 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 V ac