High-Spin Chains and Crowns from Double-Exchange Mechanism

Abstract

This article addresses the question of the possibility of obtaining high-spin chains and crowns of magnetic units s = 1 from doped (by a hole) antiferromagnetic architectures. It aims at determining the range of values of the double-exchange model interactions for which these molecules exhibit a high-spin ground state. Several chains and crowns of sizes varying between three to seven magnetic sites have been studied using a refined double-exchange model. It is shown that, for physical values of the parameters, linear chains of three, four and five sites are likely to adopt the highest spin state. For chains of six sites, small values of magnetic couplings are needed to get the highest spin, but it would be easy to get an S = 3/2 ground state. For systems of seven (or slightly more) sites, the highest spin state becomes non accessible but S = 5/2 states are likely to be obtained. Surprisingly, the physics of crowns is substantially different. The same trends are observed for even-number systems but with a larger double-exchange regime. At variance, odd-number systems do not exhibit a double-exchange mechanism for low values of the magnetic couplings. These observations are rationalized from an analysis of the computed spectra and wave functions.

Modelling spin Hamiltonian parameters of molecular nanomagnets

“…This is necessarily seen in transition metal compounds possessing two or more metal sites of varying non-integer oxidation numbers, known as mixed valence complexes. 213 In mixed valence complexes, double exchange (in addition to Heisenberg exchange) is generated due to the presence of an extra additional electron, which aligns the localized magnetic moments. As this additional electron maintains its spin during transfer between the metal sites, double exchange always favours the same spin orientation.…”

Restricted Open-Shell Hartree–Fock Method for a General Configuration State Function Featuring Arbitrarily Complex Spin-Couplings

“…All other geometries were calculated at the DFT level of theory employing the BP86 functional , together with Grimme’s dispersion correction − with the triple-ζ Def2-TZVP basis set together with the Def2/J auxiliary basis for the resolution of the identity approximation . The Ni chain geometry was fixed to local octahedral geometries, with only the hydrogen atoms being optimized at the same level of theory of the other geometry optimizations. The coordinates of all the geometries used in this paper can be found in the Supporting Information.…”