Uranium and manganese assembled in a wheel-shaped nanoscale single-molecule magnet with high spin-reversal barrier

Abstract

Discrete molecular compounds that exhibit both magnetization hysteresis and slow magnetic relaxation below a characteristic 'blocking' temperature are known as single-molecule magnets. These are promising for applications including memory devices and quantum computing, but require higher spin-inversion barriers and hysteresis temperatures than currently achieved. After twenty years of research confined to the d-block transition metals, scientists are moving to the f-block to generate these properties. We have now prepared, by cation-promoted self-assembly, a large 5f-3d U(12)Mn(6) cluster that adopts a wheel topology and exhibits single-molecule magnet behaviour. This uranium-based molecular wheel shows an open magnetic hysteresis loop at low temperature, with a non-zero coercive field (below 4 K) and quantum tunnelling steps (below 2.5 K), which suggests that uranium might indeed provide a route to magnetic storage devices. This molecule also represents an interesting model for actinide nanoparticles occurring in the environment and in spent fuel separation cycles.

Radical ligand-containing single-molecule magnets

“…The coupling constant for the Np IV -Np V interaction was reported as J = 7.5 cm −1 , an order of magnitude larger than the typical superexchange in multinuclear lanthanide complexes, ultimately leading to a high relaxation barrier of U eff = 97 cm −1 . Superexchange was also observed in a large 5f-3d U 12 Mn 6 wheel-shaped cluster complex, exhibiting open hysteresis loops up to 4 K and a spin relaxation barrier of 99 cm −1 , representing the highest barrier yet observed in an actinidecontaining single-molecule magnet [362].…”

“…Given the observed strong coupling in actinide complexes induced by exchange or superexchange involving cation-cation interactions [352,[362][363][364], the use of radical ligands promises to yield even higher magnetic blocking temperatures. Indeed, owing to their large single-ion anisotropies and the greater radical extension of 5f valence orbitals, the better overlap between metal and radical ligands should lead to much stronger coupling than observed for lanthanide-based systems.…”

Future Directions for Transuranic Single Molecule Magnets

“…The slow progress in the field is in part due to the relative smallness of the actinide scientific community, and to the fact that only a handful of laboratories are equipped to handle transuranic elements, so that most of the reported work concerns uranium complexes only. SMM behaviour has actually been observed in several monometallic U III [13] and U V [14] complexes and in heterometallic coordination compounds containing U V and either Mn II or Dy III cations [15][16][17].…”

Evolvement of molecular nanomagnets in China

“…Significantly, studies on the lanthanide ions have led to an enormous increase in both the U eff and T B : several hundreds of wave numbers for U eff and 14 K for T B [10,11]. Recently, the SMMs with actinide became attractive systems with interesting magnetic properties [12]. Besides these two sources of anisotropy, the incorporation of the 4d/5d metal ions with strong anisotropic coupling has also been explored.…”