J. Phys. IV France
Volume 114, April 2004
Page(s) 125 - 126

J. Phys. IV France
114 (2004) 125
DOI: 10.1051/jp4:2004114027

Low frequency dielectric properties in a ferromagnetic semiconductor (ED-TTFVO) 2FeBr 4 with permanent electric dipoles

E. Negishi1, S. Yabuta1, T. Matsumoto2, T. Sugimoto2 and N. Toyota1

1  Physics Department, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
2  Research Institute for Advanced Science and Technology, Osaka Prefecture University, Osaka 599-8570, Japan

We have measured the dielectric constant $\varepsilon $ 1 and conductivity $\sigma $ 1 along the b-axis in a ferromagnetic ( $T_{\rm c} = 1$ K) semiconductor (ED-TTFVO) 2FeBr 4 with permanent electric dipoles, using a three-terminal capacitance bridge at frequencies from 10 Hz to 2.8 kHz at excitation voltages from 25-250 mV. The temperature dependence of $\varepsilon $ 1, which is as large as 10 4 - 105, shows a broad peak at Tp associated with a hump at  $T_{\rm h}$ below $T_{\rm p}$. These two anomalous temperatures increase with frequency; $T_{\rm p} = 15$ K (10 Hz)-40 K (2.8 kHz) and $T_{\rm h} = 8$ K (10 Hz)-17 K (2.8 kHz). Furthermore, $\varepsilon $ 1 and  $\sigma $ 1 exhibit a remarkable non-linearity with the excitation voltage. These characteristic behaviors are reminiscent of a ferroelectric relaxor. Key words. (ED-TTFVO) 2FeBr 4, Dielectric constant, Molecular electric dipoles, $\pi -d$ system, Ferromagnetism, Ferroelectric relaxor.

© EDP Sciences 2004