Europhys. Lett.
Volume 65, Number 5, March 2004
Page(s) 705 - 711
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 February 2004
Europhys. Lett., 65 (5) , pp. 705-711 (2004)
DOI: 10.1209/epl/i2003-10164-5

Observation of a transient magnetization plateau in a quantum antiferromagnet on the Kagomé lattice

Y. Narumi1, K. Katsumata1, Z. Honda2, J.-C. Domenge3, P. Sindzingre3, C. Lhuillier3, Y. Shimaoka4, T. C. Kobayashi4 and K. Kindo4

1  RIKEN Harima Institute - Mikazuki, Sayo, Hyogo 679-5148, Japan
2  Faculty of Engineering, Saitama University - Shimo-Okubo, Saitama 338-8570, Japan
3  Laboratoire de Physique Théorique des Liquides, Université P. et M. Curie and UMR 7600 of CNRS, case 121 - 4 Place Jussieu, 75252 Paris Cedex, France
4  KYOKUGEN, Osaka University - Toyonaka, Osaka 560-8531, Japan

(Received 25 August 2003; accepted in final form 15 December 2003)

The magnetization process of an $S=\frac{1}{2}$ antiferromagnet on the Kagomé lattice, $\chem{[Cu_3(titmb)_2(OCOCH_3)_6]\cdot
H_2O}$ {titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6 trimethylbenzene}, has been measured at very low temperatures in both pulsed and steady fields. We have found a new dynamical behavior in the magnetization process. A plateau at one third of the saturation magnetization $M_{\ab{s}}$ appears in the pulsed-field experiments for intermediate sweep rates of the magnetic field and disappears in the steady-field experiments. A theoretical analysis using exact diagonalization yields $J_1=-19\pm 2$ $\un{K}$ and $J_2=6\pm 2$ $\un{K}$, for the nearest-neighbor and second-nearest-neighbor interactions, respectively. This set of exchange parameters explains the very low saturation field and the absence of the plateau in the thermodynamic equilibrium as well as the two-peak feature in the magnetic heat capacity observed by Honda et al. (Z. Honda et al. , J. Phys. Condens. Matter 14 (2002) L625). Supported by numerical results we argue that a dynamical order by disorder phenomenon could explain the transient appearance of the $M_{\ab{s}}/3$ plateau in pulsed-field experiments.

75.10.Jm - Quantized spin models.
75.50.Ee - Antiferromagnetics.
75.60.Ej - Magnetization curves, hysteresis, Barkhausen and related effects.

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