In magnetic substance molecular magnets remain in a closed rim form when it is not a magnet
Answers
The magnetic coupling between the spins of the metal ions is mediated by superexchange interactions and can be described by the following isotropic Heisenberg Hamiltonian:
{\displaystyle {\hat {\mathcal {H}}}_{HB}=-\sum _{i<j}J_{i,j}\mathbf {S} _{i}\cdot \mathbf {S} _{j},} {\displaystyle {\hat {\mathcal {H}}}_{HB}=-\sum _{i<j}J_{i,j}\mathbf {S} _{i}\cdot \mathbf {S} _{j},}
where {\displaystyle J_{i,j}} J_{i,j} is the coupling constant between spin i (operator {\displaystyle \mathbf {S} _{i}} {\mathbf {S}}_{i}) and spin j (operator {\displaystyle \mathbf {S} _{j}} {\displaystyle \mathbf {S} _{j}}). For positive J the coupling is called ferromagnetic (parallel alignment of spins) and for negative J the coupling is called antiferromagnetic (antiparallel alignment of spins).
a high spin ground state,
a high zero-field-splitting (due to high magnetic anisotropy), and
negligible magnetic interaction between molecules.
The combination of these properties can lead to an energy barrier, so that at low temperatures the system can be trapped in one of the high-spin energy wells.[1] [2] [3] [4] [5]