Magnetic and structural properties of an octanuclear Cu(II)S=1/2mesoscopic ring: Susceptibility and NMR measurements
| Autor: | Dante Gatteschi, Donella Rovai, Andrea Caneschi, Z. H. Jang, Alessandro Lascialfari, Pietro Carretta, Ferdinando Borsa, Andrea Cornia |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Physical Review B. 61:6839-6847 |
| ISSN: | 1095-3795 0163-1829 |
| DOI: | 10.1103/physrevb.61.6839 |
| Popis: | Magnetic susceptibility, ${}^{1}\mathrm{H}$ NMR and ${}^{63}\mathrm{Cu}$ NMR-NQR experiments on two slightly different species of the molecular $S=1/2$ antiferromagnetic (AF) ring Cu8, $[{\mathrm{Cu}}_{8}{(\mathrm{dmpz})}_{8}{(\mathrm{OH})}_{8}{]\mathrm{\ensuremath{\cdot}}2\mathrm{C}}_{5}{\mathrm{H}}_{5}\mathrm{N}$ (Cu8P) and $[{\mathrm{Cu}}_{8}{(\mathrm{dmpz})}_{8}{(\mathrm{OH})}_{8}{]\mathrm{\ensuremath{\cdot}}2\mathrm{C}}_{5}{\mathrm{H}}_{5}{\mathrm{NO}}_{2}$ (Cu8N), are presented. The magnetic energy levels are calculated exactly for an isotropic Heisenberg model Hamiltonian in zero magnetic field. From the magnetic susceptibility measurements we estimate the AF exchange coupling constant $J\ensuremath{\sim}1000\mathrm{K}$ and the resulting gap $\ensuremath{\Delta}\ensuremath{\sim}500\mathrm{K}$ between the ${S}_{T}=0$ ground state and the ${S}_{T}=1$ first excited state. The ${}^{63,65}\mathrm{Cu}$ NQR spectra indicate the presence of four crystallographically inequivalent copper nuclei in each ring. From the combination of the ${}^{63}\mathrm{Cu}$ NQR spectra and of the ${}^{63}\mathrm{Cu}$ NMR spectra at high magnetic field, we estimate the quadrupole coupling constant ${v}_{Q}$ of each site and the average asymmetry parameter \ensuremath{\eta} of the electric-field gradient tensor. The nuclear spin-lattice relaxation rate (NSLR) decreases exponentially on decreasing temperature for all nuclei investigated. The gap parameter extracted from ${}^{63}\mathrm{Cu}$ NQR-NSLR is the same as for the susceptibility while a smaller value is obtained from the ${}^{63}\mathrm{Cu}$ NMR-NSLR in an external magnetic field of 8.2 T. |
| Databáze: | OpenAIRE |
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