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

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

Corresponding author: narumi@mag.rcem.osaka-u.ac.jp

Received: 25 August 2003
Accepted: 15 December 2003

Abstract

The magnetization process of an antiferromagnet on the Kagomé lattice, {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 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 and , 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 plateau in pulsed-field experiments.