Eur. Phys. J. B 11, 217-225 (1999)
https://doi.org/10.1007/s100510050932

Magnetic anisotropy and low-frequency dielectric response of weak ferromagnetic phase in k-(BEDT-TTF)₂Cu[ N(CN)₂] Cl, where BEDT-TTF is Bis(ethylenedithio)tetrathiafulvalene

¹ Institute of Physics, P.O. Box 304, 10000 Zagreb, Croatia
² Faculty of Civil Engineering, University of Maribor, 2000 Maribor, Slovenia
³ 3. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany
⁴ Anorganisch-chemiches Institut, Universität Heidelberg, 69120 Heidelberg, Germany

Corresponding author: ^a stomic@ifs.hr

Received: 15 June 1998
Revised: 1 February 1999
Published online: 15 September 1999

Abstract

We report a detailed characterization of the magnetism and AC transport in single crystals of the organic conductor κ-(BEDT-TTF)₂Cu[ N(CN)₂] Cl by means of magnetic anisotropy measurements and low-frequency dielectric spectroscopy. Magnetic anisotropy obeys Curie-Weiss law with negative Curie-Weiss temperature in the temperature range 300 K-70 K. An antiferromagnetic transition with concomitant canted antiferromagnetic state is established at 22 K. A large hysteresis in the spin-flop transition and magnetic field reversal of the weak ferromagnetic magnetization are documented for the first time. A broad dielectric relaxation mode of moderate strength () emerges at 32 K, and weakens with temperature. The mean relaxation time, much larger than that expected for single-particle excitations, is thermally activated in a manner similar to the DC conductivity and saturates below 22 K. These features suggest the origin of the broad relaxation as an intrinsic property of the weak ferromagnetic ground state. We propose a charged domain wall in a random ferromagnetic domain structure as the relaxation entity. We argue that the observed features might be well described if Dzyaloshinsky-Moriya interaction is taken into account. A Debye relaxation with similar temperature dependence was also observed and seems to be related to an additional ferromagnetic-like, most probably, field-induced phase. We tentatively associate this phase, whose tiny contribution was sample dependent, with a Cu²⁺ magnetic subsystem.