Intra-molecular origin of the spin-phonon coupling in slow-relaxing molecular magnets

Abstract

The design of slow relaxing magnetic molecules requires the optimization of internal molecular vibrations to reduce spin-phonon coupling.

A Pseudo‐Octahedral Cobalt(II) Complex with Bispyrazolylpyridine Ligands Acting as a Zero‐Field Single‐Molecule Magnet with Easy Axis Anisotropy

“…This behavior has been observed in other highly anisotropic complexes [56] and attributed to the efficiency of nonresonant optical phonons, [46,47] which cannot be neglected if anharmonicity is taken into account.E ven if the optimization of the magnetization dynamics of SMM requires the control of severalf actors, such as tunneling mechanismsa nd vibrational modes, the rational design of the coordination environmentr emains the first step to be ablet og enerate magnetic bistability through the appropriate sign of the magnetic anisotropy.A no ctahedral cobalt(II) environment, despite its large orbital contribution, has so far eluded the successful provision of examples of genuine SMM behavior.T he combination of ad etailed experimental investigation with theoretical modeling at different levels, as described herein,c an provide valuable hints forarational design of cobalt(II)-based SMMs. In an applied magnetic field, the behavior deviated from the Arrhenius behavior expected for an ideal SMM as the highest estimation of the energy barriert ob eo vercome is significantly smaller than the separation between the ground and first doublets.…”

“…In an applied magnetic field, the behavior deviated from the Arrhenius behavior expected for an ideal SMM as the highest estimation of the energy barriert ob eo vercome is significantly smaller than the separation between the ground and first doublets. This behavior has been observed in other highly anisotropic complexes [56] and attributed to the efficiency of nonresonant optical phonons, [46,47] which cannot be neglected if anharmonicity is taken into account.E ven if the optimization of the magnetization dynamics of SMM requires the control of severalf actors, such as tunneling mechanismsa nd vibrational modes, the rational design of the coordination environmentr emains the first step to be ablet og enerate magnetic bistability through the appropriate sign of the magnetic anisotropy.A no ctahedral cobalt(II) environment, despite its large orbital contribution, has so far eluded the successful provision of examples of genuine SMM behavior.T he combination of ad etailed experimental investigation with theoretical modeling at different levels, as described herein,c an provide valuable hints forarational design of cobalt(II)-based SMMs.…”

“…Treatmento ft he isothermal c M ''(n)p lots with ag eneralized Debye model allowed us to extract the relaxation time (t)a t each temperature. This deviation from the simple Arrhenius-like behavior can be due to processes induced by either nonresonant spin-phonon interactions in the solid state [46,47] or tunnel mechanisms. At the highest-temperature interval between 6.5 and 9.5 K, the plot appears to be linear and can be suitably fitted with the Arrhenius law (lnt = lnt 0 + U eff /k B T)w ith the best-fit parameters U eff /k B = 43.6(2) Ka nd t 0 = 1.2(2) 10 À7 s (green line in Figure 6b).…”

First-Principles Investigation of Spin–Phonon Coupling in Vanadium-Based Molecular Spin Quantum Bits

“…The calculation of the spin-phonon coupling coefficients is performed following a tensor differentiation procedure as described in a previous report on Single Molecule Magnets (SMMs). [36] This procedure is here applied to the Landé g tensor that describes the coupling between the spins and an external magnetic field. Each element of the Landé tensor of the equilibrium structure (indicated by the subscript 0) is differentiated with respect to the 3M atomic Cartesian positions (∂g/∂X) 0 , where M is the number of atoms in the molecule, instead of the 3N unit-cell vibrational coordinates, q α , [37] (see Figure S2 in SI).…”

“…The approximations involved in this approach have been discussed elsewhere. [36] Understanding the interactions contributing to V α ab is the main focus of this work. In order to understand the origin of the spin-phonon coupling is necessary to discuss the nature of the spin Hamiltonian that enters in Equation 5.…”