Electronic and Magnetic Signatures of Low-Lying Spin-Flip Excitonic States of Mn 12O 12-Acetate

Abstract

Based upon recent work on the Mn₃ monomer and the Mn(taa) there is an expectation that Mn^III centers can exist in local spin states with S=2 (3d↑↑↑↑) or S=1 (3d↑↑↑↓). While the high-spin states are usually more stable based on Hunds first rule, the Mn₃ monomer and the Mn(taa) provide examples where the presence of S=1 states is energetically favorable. In this paper we examine the possibility that such S=1 centers, referred to as Spin-Flip Excitons (SFE) can exist in the Mn ₁₂O₁₂(COOR)₁₆[H₂O]₂ molecule (Mn ₁₂-Ac). Our results shown that up to eight of these excitons can exist as metastable electronic states. We examine the relatively stability per exciton as a function of the the number of these excitons and determine spin-crossover paths between the the Mn₁₂-Ac zero-exciton ground state (S=10), a four-exciton state (S=6) and an eight-exciton state. The magnetic anisotropy of these states decreases monotonically and significantly with the number of excitons.