Eur. Phys. J. B 25, 39-51 (2002)
https://doi.org/10.1140/e10051-002-0006-x

Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y₂BaNi_1-xZn_xO₅

¹ Centre de Recherches sur les Très Basses Températures (CRTBT) (UPR 5001 du CNRS, Laboratoire conventionné avec l'Université Joseph Fourier) , CNRS BP 166X, 38042 Grenoble Cedex, France
² Institut des Matériaux Jean Rouxel, Université de Nantes-CNRS, 44322 Nantes Cedex 3, France

Corresponding author: ^a melin@polycnrs-gre.fr

Received: 17 July 2001
Published online: 15 January 2002

Abstract

We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y₂BaNi_1-xZn_xO₅. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature. We obtain a Curie-Weiss susceptibility as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order. We explain how to obtain the “impurity” susceptibility by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental data are well fitted by . In the temperature range [100 mK, 1 K] the experimental data are well fitted by , where T_c increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments. We also obtain a maximum in the temperature dependence of the ac-susceptibility which suggests the existence of antiferromagnetic correlations at very low temperature.