Intermolecular mechanism for multiple maxima in molecular dynamic susceptibility

Abstract

A simple two-level system is introduced to demonstrate the existence of the intermolecular mechanism of the appearance/disappearance of multiple maxima in molecular dynamic susceptibility at low temperature. With a minimum of two relaxation processes, quantum tunneling induced by the nuclear spin bath, and the direct process due to the spin-phonon interaction, we prove that the existence of a sufficiently wide dipolar field distribution in the experimental sample is the main cause of this phenomenon in zero or weak applied dc field. The correlations between the phenomenon and the applied dc field, temperature, or magnetic dilution of the sample are also investigated. Application to several experimental systems has shown a good agreement between the proposed theory and experiments. Cases with a more complex multiplet spectrum, more relaxation processes, and the possibility of more maxima in the molecular dynamic susceptibility are discussed.

Triplet‐State Position and Crystal‐Field Tuning in Opto‐Magnetic Lanthanide Complexes: Two Sides of the Same Coin

“…Before going through the dynamic magnetic properties of Tb‐tfac and Tb‐hfac, the field and temperature dependence of two maxima in χ ′′ observed for Tb‐acac should be noted as this phenomenon was clearly pronounced in Tb‐acac compared to Tb‐tfac and Tb‐hfac. Similar kinds of field dependence of χ ′′ with two maxima have been observed before for other lanthanide SMMs and it might arise from intermolecular dipolar interactions between magnetic centres in a sample . In the low‐temperature regime, intermolecular dipolar interactions can generate a sufficiently wide dipolar field distribution in the sample, which results in two distinct domains of the total magnetic field in which one relaxation process dominates the other (QTM vs. direct) .…”

“…Although the intermolecular dipolar couplings clearly influence almost as equally as intramolecular magnetic interactions to the magnetic properties of Tb‐acac as mentioned above, it cannot be unambiguously concluded from their small values (Table S5 in the Supporting Information) and their total sum ( J intra+inter_dip =0.16 cm −1 ) if the two observed maxima in χ ′′ originate from the sufficiently wide dipolar field distribution within the sample. Moreover, in order to see two maxima in χ ′′, the ground quasi‐doublet should be well separated from the first excited quasi‐doublet, otherwise the Orbach process may contribute to the formation or the destruction of the two maxima in conjunction with the QTM and direct process . Because the ground and first excited quasi‐doublets are not separated by several hundred wavenumbers but only by 101 cm −1 in Tb‐acac as shown by the ab initio calculations, we cannot completely rule out the involvement of the Orbach process to the presence of the two maxima in χ ′′ at the low‐temperature regime where dynamic magnetic measurement were carried out.…”

Asymmetric Ring Opening in a Tetrazine‐Based Ligand Affords a Tetranuclear Opto‐Magnetic Ytterbium Complex

“…In fact, the most intense component of the 2 F 5/2 → 2 F 7/2 multiplet is composed of two closely spaced sharp peaks centred, respectively at 10 248 and 10 223 cm −1 , which likely arise from two non‐equivalent Yb 3+ ions (Figure 4). Moreover, the presence of two maxima in the field dependence measurements of χ’’ might indicated the presence of two distinct magnetic centres in 1 although two different maxima showing either temperature or field dependence or both can also originate from the sufficiently wide dipolar field distribution in the sample [61] . The dipolar field can create two distinct domains of the total magnetic interaction where either QTM, direct, or Raman process dominates each other at low temperature regime.…”

Dysprosium Single-Molecule Magnets Involving 1,10-Phenantroline-5,6-dione Ligand

“…Such a hypothesis is supported by the difference of the frequency dependence of χ M " at 2 K under a 200 Oe applied field (Figure 7), which displayed a clear double contribution at frequencies of 2.5 and 400 Hz for 1 but not for 2. Such an observation should be an indication of stronger intermolecular dipolar interactions in 1 than in 2 [60].…”