Single-molecule magnet

Single-molecule magnets (SMM) are a class of metalorganic compounds, that show superparamagnetic behavior below a certain blocking temperature at the molecular scale. In this temperature range, SMMs exhibit magnetic hysteresis of purely molecular origin. Contrary to conventional bulk magnets and molecule-based magnets, collective long-range magnetic ordering of magnetic moments is not necessary.

The magnetic coupling between the spins of the metal ions is mediated via superexchange interactions and can be described by the following isotropic Heisenberg Hamiltonian:

where ${\displaystyle J_{i,j}}$ is the coupling constant between spin i (operator ${\displaystyle \mathbf {S} _{i}}$) and spin j (operator ${\displaystyle \mathbf {S} _{j}}$). 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).

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