Abstract
The magnetic structures of the hexagonal and oxides (space group have been studied by neutron-diffraction experiments on powder samples. This study has been complemented with magnetic susceptibility and specific-heat measurements. They confirm that and become ordered below K and K, respectively, according to a triangular antiferromagnetic structure. The latter compound undergoes a second magnetic transition below 75 K, corresponding to a spin reorientation. The presence of weak ferromagnetism of Dzialoshinskii-Moriya type is observed in all the ordered region for the Sc material. In both compounds the moments are contained in the plane and oriented perpendicular or parallel to the [100] directions. The low-temperature ordered moments are and at K. The different behavior observed in the thermal evolution of the magnetic structure of both compounds is discussed in terms of geometrical parameters determined from high-resolution structural data. The origin of the weak ferromagnetism in is also analyzed.
- Received 31 March 2000
DOI:https://doi.org/10.1103/PhysRevB.62.9498
©2000 American Physical Society