Magnetic relaxation pathways in lanthanide single-molecule magnets

Abstract

Single-molecule magnets are compounds that exhibit magnetic bistability caused by an energy barrier for the reversal of magnetization (relaxation). Lanthanide compounds are proving promising as single-molecule magnets: recent studies show that terbium phthalocyanine complexes possess large energy barriers, and dysprosium and terbium complexes bridged by an N2(3-) radical ligand exhibit magnetic hysteresis up to 13 K. Magnetic relaxation is typically controlled by single-ion factors rather than magnetic exchange (whether one or more 4f ions are present) and proceeds through thermal relaxation of the lowest excited states. Here we report polylanthanide alkoxide cage complexes, and their doped diamagnetic yttrium analogues, in which competing relaxation pathways are observed and relaxation through the first excited state can be quenched. This leads to energy barriers for relaxation of magnetization that exceed 800 K. We investigated the factors at the lanthanide sites that govern this behaviour.

An electrostatic model for the determination of magnetic anisotropy in dysprosium complexes

“…The presence of the other charged ligands and the trivalent dysprosium ions is a small perturbation in this case, because of the strongly directional nature of the almost linear i PrO À -Dy-O 2 À axis. The results obtained using our electrostatic model compare extremely well with those obtained using ab initio calculations 33 (see Supplementary Table S19).…”

“…Calculating the ab initio properties of the following polymetallic complexes is extremely computationally expensive. Hence, to demonstrate the power of our simple 32,33). The methodology for the calculation of the electrostatic anisotropy axes in polymetallic complexes is identical to that of monometallic complexes and is performed for each Dy III ion independently.…”

Direct measurement of dysprosium(III)˙˙˙dysprosium(III) interactions in a single-molecule magnet

“…F ascinating physics has been observed in lanthanide-based molecules ranging from single nuclear spin detection and manipulation 1,2 , blocking of magnetization at unprecedentedly high temperatures for a molecule 3,4 , magnetic memory in chiral systems with a non-magnetic ground state 5,6 and energy barriers for loss of magnetization, U eff , an order of magnitude higher than observed for polymetallic d-block cages 7,8 . A diverse range of applications has been envisioned for lanthanide (Ln) containing molecules, including use as qubits for quantum information processing 9,10 and prototype devices such as molecular spin valves 11 and transistors 1 have been reported.…”

“…In other compounds weak Ln Á Á Á Ln interactions can shift the zero-field quantum tunnelling step to a finite field, known as exchange biasing 15 , with different effects on cryogenic magnetization curves depending on the sign of the exchange 16,17 or even mask single-ion slow relaxation modes 18 . More frequently, however, Ln Á Á Á Ln interactions increase quantum tunnelling rates, leading to apparently lower U eff values when compared with paramagnetic Ln ions doped into a diamagnetic lattice 8,17,19 . Understanding how Ln Á Á Á Ln interactions can have such different and seemingly contradictory influences is important for improving the performance of Ln SMMs.…”

Multiple Magnetization Reversal Channels Observed in a 3d-4f Single Molecule Magnet

“…Manifestation of multiple relaxation channels is not unusual in lanthanide based complexes [25,30]. However identification and contribution of the individual processes has proven to be quite tricky, due to the complex energetic structure of these ions.…”