The Kahn degenerate frustration points and the Lieb-Mattis level order in heterometallic wheel molecules with competing interactions

Abstract

Abstract The energy structure of heterometallic molecules with wheel topology is considered within the quantum Heisenberg spin model, using mostly the algebraic methods. In our approach, the central spin is coupled to the peripheral ones by the interaction parameter J ′ , whereas the latter located at the perimeter are subjects to the nearest-neighbour interaction J. The systems are frustrated in the regime J > 0 irrespective of the sign of J ′ and the ground state total spin quantum numbers form a universal sequence consisting of a definite number of steps as a function of the ratio α = J ′ / J . The Kahn degenerate frustration points occur at the discontinuous jumps or special symmetry junctures. In addition, the Lieb-Mattis level order is revealed despite the lack of bipartiteness, and existence of broad plateaus in the magnetisation profiles is also indicated.