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Understanding how magnetic nuclei affect spin relaxation is vital for designing robust spin coherence in magnetic materials and molecules. A key question is the extent that magnetic nuclei close to a spin (e.g., in the ligand shell of a metal complex) influence relaxation and how it varies over different classes of nuclei. Herein, we apply high-field EPR, X-band EPR, and ac magnetic susceptibility techniques to a family of five V(IV) complexes of the type [V(C6X4O2)3]2β, featuring five different sets of 12 nuclear spins on the ligand shell: X = 1H (1), 2H (2), 19F (3), 35/37Cl (4), and 79/81Br (5). We found several unanticipated results in these studies. For example, at high-field/-frequency, we found that compound 1, with the highest-magnetic-moment ligand nuclear spins, exhibits the longest phase memory relaxation times of the series. Furthermore, at lower fields, we found that the spinβlattice relaxation time and its field dependence were ligand-dependent, despite no obvious change in electronic structure across the five species. Based on this data, structural comparisons, and Raman spectroscopic data, we tentatively conclude that the spinβlattice relaxation properties of 1β5 stem from fine-tuning of the local magnetic environment with changing identity of the X atoms.
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This content will become publicly available on December 1, 2025
19F NMR and Defect Spins in Vacuum-Annealed LaO0.5F0.5BiS2
We report results of magnetization and 19F NMR measurements in the normal state of as-grown vacuum-annealed LaO0.5β’F0.5β‘BiS2. The magnetization is dominated by a temperature-independent diamagnetic component and a field- and temperature-dependent paramagnetic contribution ππβ‘(π»,π) from a βΌ1000 ppm concentration of local moments, an order of magnitude higher than can be accounted for by measured rare-earth impurity concentrations. ππβ‘(π»,π) can be fit by the Brillouin function π΅π½β‘(π₯) or, perhaps more realistically, a two-level tanhβ‘(π₯) model for magnetic Bi 6β’π ions in defect crystal fields. Both fits require a phenomenological Curie-Weiss argument π₯=πeffβ’π»β‘/(π+ππ), ππβ1.7 K. There is no evidence for magnetic order down to 2 K, and the origin of ππ is not clear. 19F frequency shifts, linewidths, and spin-lattice relaxation rates are consistent with purely dipolar 19F/defect-spin interactions. The defect-spin correlation time ππβ‘(π) obtained from 19F spin-lattice relaxation rates obeys the Korringa relation ππβ’π=const, indicating the relaxation is dominated by conduction-band fluctuations.
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- Award ID(s):
- 2112554
- PAR ID:
- 10609942
- Publisher / Repository:
- American Physical Society Publishing
- Date Published:
- Journal Name:
- Physical Review B
- Volume:
- 110
- Issue:
- 23
- ISSN:
- 2469-9950
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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