Eur. Phys. J. B 18, 39-47 (2000)
https://doi.org/10.1007/s100510070075

Triangular antiferromagnetic order in the honeycomb layer lattice of ErCl₃

¹ Department for Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3000 Bern 9, Switzerland
² Laboratory for Neutron Scattering, Paul Scherrer Institute and ETH Zürich, 5232 Villigen PSI, Switzerland
³ Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9, France
⁴ Hahn-Meitner Institute, Glienicker Strasse 100, 14109 Berlin, Germany

Received: 1 December 1999
Revised: 21 July 2000
Published online: 15 November 2000

Abstract

ErCl₃ crystallizes in the AlCl₃-type layer structure. The crystal structure was refined in the paramagnetic state by powder neutron diffraction. The monoclinic lattice parameters at 1.5 K are a = 6.8040(3) Å, b = 11.7456(5) Å, c = 6.3187(3) Å and . The space group is C2/m. Short-range, predominantly in-plane, magnetic ordering occurs above 350 mK up to several Kelvin. Below mK a three-dimensional antiferromagnetic order with a propagation vector of sets in. The magnetic structure of ErCl₃ was determined by powder and single-crystal neutron diffraction at temperatures down to 45 mK. The Er³⁺ ions are located on two-dimensional honeycomb layers in the a-b plane. There are two antiferromagnetically coupled triangular sublattices which form right- and left-handed helices along the c-axis. The magnetic moments are oriented in the a-b plane and amount to 3.3(1) at saturation. From the temperature dependence of the integrated neutron magnetic peak intensity a critical exponent (2) was derived for the magnetic phase transition.