Abstract
In a recent paper [J. S. Gardner et al., Phys. Rev. Lett. 82, 1012 (1999)] it was found that the magnetic moments in the antiferromagnetic pyrochlore lattice of corner-sharing tetrahedra remain in a collective paramagnetic state down to 70 mK. In this paper we present results from dc magnetic susceptibility, specific-heat data, inelastic neutron-scattering measurements, and crystal-field calculations that strongly suggest that (i) the ions in possess a moment of approximatively and (ii) the ground state g-tensor is extremely anisotropic below a temperature of with Ising-like magnetic moments confined to point along a local cubic diagonal (e.g., towards the middle of the tetrahedron). Such a very large easy-axis Ising-like anisotropy along a direction dramatically reduces the frustration otherwise present in a Heisenberg pyrochlore antiferromagnet. The results presented herein underpin the conceptual difficulty in understanding the microscopic mechanism(s) responsible for failing to develop long-range order at a temperature of the order of the paramagnetic Curie-Weiss temperature We suggest that dipolar interactions and extra perturbative exchange coupling(s) beyond nearest neighbors may be responsible for the lack of ordering of
- Received 26 January 2000
DOI:https://doi.org/10.1103/PhysRevB.62.6496
©2000 American Physical Society