Abstract
The ordered perovskite of tetragonal symmetry at has been synthesized and characterized by x-ray and neutron diffraction, thermal gravimetric analysis dc susceptibility, heat capacity, and muon spin relaxation (μSR) experiments. The B site cations and appear to be ordered due the large difference in formal charge. The magnetic ions form a distorted fcc lattice of spins providing a frustrated topology of edge-shared tetrahedra. The material exhibits a weak magnetic glassiness shown by a cusp at ∼50 K in the dc susceptibility, a weak but broad heat capacity anomaly, and a low-temperature μSR line shape characteristic of a spin-glass state. A broad and strongly field- dependent maximum in the dc susceptibility suggests that magnetic correlations persist to ∼175 K, accompanied by a divergence in the field-cooled and zero-field-cooled susceptibility. The anisotropic nature of the superexchange pathways due to the tetragonal distortion is thought to disrupt the ideal frustrated environment and lead to weaker glassiness than which has and a large specific heat anomaly. In contrast, has a small anomaly, and only about 3% of the entropy is released at which is comparable to other unconventional spin glasses such as the jarosite is unusually high for this class of materials.
- Received 18 March 2003
DOI:https://doi.org/10.1103/PhysRevB.68.134410
©2003 American Physical Society