Speaker
Description
Structural, static and dynamic magnetic properties of title complex {[Ce$_2$($o$PDA)$_3$(H$_2$O)$_2$]$\cdot 2$H$_2$O}$_n$ containing O-donor ligand H$_{2o}$PDA ($o$-phenylenediacetic acid) are reported. The structure of the studied compound is formed by chains of the Ce$^{3+}$ ions linked via $o$PDA$^{2-}$ dianions which act as pentadentate ligands with bridging and chelating functions. The analysis of the temperature dependence of the effective magnetic moment enabled to estimate the energy difference between the ground and the first excited doublet $\Delta/k_B= 317$ K. Large energy separation between the two doublets was also confirmed by the evaluation of magnetic field dependence of the magnetization studied up to $5$ T at $2$ K, $5$ K and $10$ K. Persistence of quantum tunnelling at $3.5$ K up to $0.7$ T revealed by studying magnetic field dependence of the relaxation time was attributed to powder nature of the sample. Investigation of Cole-Cole diagrams supported the dominance of Debye-like relaxation suggesting rather narrow distribution of the relaxation times. Temperature dependences of the relaxation time from $2$ K to $6$ K in magnetic fields $0.1$ T and $0.35$ T were explicable assuming the coexistence of quantum tunnelling and anomalous Raman relaxation with $\tau\approx T^{5.6}$ in striking difference with $n=7$ or $n=9$ which is expected for standard Raman relaxation of non-Kramers or Kramers ions with well separated doublets. The obtained results can be interpreted assuming the coexistence of standard Raman process and the coupling of Ce$^{3+}$ ions with low-energy local vibrational modes, the latter interaction was recently proposed as governing relaxation mechanism in several Ce(III) based metal-organic frameworks [1].
Acknowledgements
This work was supported by Slovak research agency under contract APVV-22-0172 and by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00176.
References
[1] J. Torrent et al., “Cerium-Based Metal–Organic Frameworks: Unveiling the Role of Terahertz Vibrations in the Spin Relaxation Dynamics,” Inorganic Chemistry, vol. 64, no. 8. American Chemical Society (ACS), pp. 3735–3746, Feb. 18, 2025. https://doi.org/10.1021/acs.inorgchem.4c04542
