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Metal-organic frameworks (MOFs) are composed of metal centres connected by organic polytopic ligands. Their high degree of chemical tunability is reflected in a controlled wide variability of the electronic states, among which magnetism. However, the main drawback against the realization of magnetic phases with high critical temperatures is the weak magnetic coupling between the metal centres provided by the ligands. The recent report of itinerant ferromagnetism with critical temperature $T_{C}$ = 225 K in the mixed-valent Cr(tri)$_{2}$(CF$_{3}$SO$_{3}$)$_{0.33}$ (Htri, 1H-1,2,3-triazole) MOF is an exciting development of this field of research in this sense [1].
Here, we report on our extensive investigation of Cr(tri)$_{2}$(CF$_{3}$SO$_{3}$)$_{0.33}$ by means of $^{1}$H, $^{19}$F and $^{59}$Co nuclear magnetic resonance and muon-spin rotation [2]. We highlight the lack of any critical dynamics associated with the magnetic transition despite the conventional nature of the long-range ordered configuration detected by muons. The dependence of the spin-lattice relaxation rate on temperature is consistent with the development of activated slow dynamics within the paramagnetic regime. We interpret our results in terms of a disordered phase of segregated magnetic domains akin to what is realized in mixed-valent manganites.
[1] J. G. Park et al., Nature Chemistry, 13, 594 (2021).
[2] G. Prando et al., in preparation.
| giacomo.prando@unipv.it |
