Strong Axiality and Ising Exchange Interaction Suppress Zero-Field Tunneling of Magnetization of an Asymmetric Dy₂ Single-Molecule Magnet

Abstract

The high axiality and Ising exchange interaction efficiently suppress quantum tunneling of magnetization of an asymmetric dinuclear Dy(III) complex, as revealed by combined experimental and theoretical investigations. Two distinct regimes of blockage of magnetization, one originating from the blockage at individual Dy sites and the other due to the exchange interaction between the sites, are separated for the first time. The latter contribution is found to be crucial, allowing an increase of the relaxation time by 3 orders of magnitude.

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

“…Compound 3 shows very different physics from the exchange bias type of compounds, originally described by Wernsdorfer et al 33 , and also seen in {Dy 2 } complexes 16 , where a remnant magnetization is present in the open hysteresis loops; a feature not observed here because of rapid zero-field relaxation. The hypothetical compound where the tilt angle is 0°may possibly show the characteristic QTM steps at the crossing points in Supplementary Fig.…”

“…Radical bridging ligands can provide a strong magnetic exchange pathway between two lanthanide ions, leading to magnetic hysteresis at 14 K 3,4 . 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 .…”

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

“…An increasing number of ab initio CASSCF calculations 6,14,15,20,28 have shown that in most low-symmetry complexes, the ground Kramers doublet of Dy III is strongly axial with the principal values of the g-tensor approaching those of the m J ¼ ± 15 / 2 levels of the atomic multiplet 6 20). This empirical observation suggests that a simple, but appropriate, variational ansatz for the many-electron ground state wavefunction of these low-symmetry complexes consists of the atomic functions w ± (a,b) corresponding to the m J ¼ ± 15 / 2 states of the multiplet 6 H 15/2 .…”

“…Recent advances in post Hartree-Fock multi-configurational ab initio methodology have made accurate quantum chemical calculations on paramagnetic 4f compounds possible 12 . The Complete Active Space Self Consistent Field (CASSCF) method can accurately predict the magnetic properties of lanthanide complexes 13,14 , and calculations of this type have become an indispensable tool for the explanation of increasingly interesting magnetic phenomena 6,[15][16][17] . These calculations are especially useful in cases of low symmetry, where previous methods have provided intractable, over parameterized problems 18,19 .…”

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

“…More importantly, dinuclear Ln III SMMs are very important model systems to answer basic questions regarding single-ion relaxation vs. slow magnetic relaxation arising from the molecule as an entity. Thus, Ln III 2 complexes are highly desirable [10][11][12][13][14][15][16][17][18][19][20]. Another interesting area to which dinuclear lanthanide(III) complexes (and also mononuclear ones) are relevant is quantum computation; Ln III ions are promising candidates for encoding quantum information [21,22].…”