Abstract
We study the electronic structure and magnetic interactions in methylamine-intercalated orthorhombic alkali-doped fullerene within the density functional theory. As in the simpler ammonia intercalated compound , the orthorhombic crystal-field anisotropy lifts the triple degeneracy at the point and drives the system deep into the Mott-insulating phase. However, the computed and conduction electron bandwidth cannot alone account for the abnormally low experimental Néel temperature, K, of the methylamine compound, compared to the much higher value K of the ammonia one. Significant interactions between and are responsible for the stabilization of particular fullerene-cage distortions and the ensuing low-spin state. These interactions also seem to affect the magnetic properties, as interfullerene exchange interactions depend on the relative orientation of deformations of neighboring molecules. For the ferro-orientational order of -K groups we find an apparent reduced dimensionality in magnetic exchange interactions, which may explain the suppressed Néel temperature. The disorder in exchange interactions caused by orientational disorder of -K groups could further contribute to this suppression.
- Received 11 June 2012
DOI:https://doi.org/10.1103/PhysRevB.86.085109
©2012 American Physical Society