Diabolical points in magnetic molecules: An exactly solvable model - art. no. 064422

The magnetic molecule Fe-8 has a rich pattern of degeneracies in its magnet ic spectrum as the static magnetic held applied to it is varied. The points of degeneracy, or diabolical points in the magnetic field space. are found exactly in the simplest model Hamiltonian for this molecule. They are show n to form a perfect centered rectangular lattice, and to be multiply diabol ical in general. The multiplicity is found. An earlier semiclassical soluti on to this problem is thereby shown to be exact in leading order in 1/J whe re J is the spin.