NMR evidence for f -electron excitations in the multipolar ground state of NpO2
| Autor: | S. Kambe, R. E. Walstedt, Yo Tokunaga, H. Sakai |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
Physics
02 engineering and technology Electron 021001 nanoscience & nanotechnology Coupling (probability) 01 natural sciences Paramagnetism symbols.namesake Dipole 0103 physical sciences symbols Atomic physics 010306 general physics 0210 nano-technology Ground state Hamiltonian (quantum mechanics) Magnetic dipole–dipole interaction Spin-½ |
| Zdroj: | Physical Review B. 98 |
| ISSN: | 2469-9969 2469-9950 |
| DOI: | 10.1103/physrevb.98.144403 |
| Popis: | An analysis is presented of the $^{237}\mathrm{Np}\ensuremath{-}^{17}\mathrm{O}$ cross-relaxation (CR) process at temperatures below $T=10$ K that was reported [Tokunaga et al., Phys. Rev. B 74, 064421 (2006)] in $^{17}\mathrm{O}$ NMR studies of ${\mathrm{NpO}}_{2}$. The CR evidently results from $^{237}\mathrm{Np}$ spin fluctuations driven by indirect spin-spin interactions analogous to the Suhl-Nakamura [Nakamura, Prog. Theor. Phys. 20, 542 (1958)] effect in conventional magnets. Here, however, there is a body of evidence that the interacting ${\mathrm{Np}}^{4+}$ ions are in a magnetic, rank-5 dotriakontadipolar ground state [Santini et al., Phys. Rev. Lett. 97, 207203 (2006); Magnani et al., Phys. Rev. B 78, 104425 (2008)]. Owing to the observed exponential form of the fluctuation spectrum, it is possible to evaluate explicitly the CR bandwidth in terms of any specified $^{237}\mathrm{Np}\ensuremath{-}^{237}\mathrm{Np}$ (spin-spin) coupling Hamiltonian. We model the latter as an enhanced dipolar coupling. The enhancement is concluded to be compound, with the ``enlarged nuclear moment'' mechanism identified in the paramagnetic state [Tokunaga et al., Phys. Rev. B 74, 064421 (2006)] responsible for a factor $\ensuremath{\sim}22$, while the indirect $^{237}\mathrm{Np}\ensuremath{-}^{237}\mathrm{Np}$ coupling effect is found to be $\ensuremath{\sim}240$ times the amplitude of the classical dipolar interaction. We suggest that these results are consistent with the identification of a magnetic rank 5 multipolar ground state [Magnani et al., Phys. Rev. B 78, 104425 (2008)] for ${\mathrm{NpO}}_{2}$. |
| Databáze: | OpenAIRE |
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