J. Phys. Soc. Jpn. 75S (2006) pp. 146-148  |Previous Article| |Next Article|  |Table of Contents|
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Proc. of 5th Int. Symposium on ASR-WYP-2005 – Advances in the Physics and Chemistry of Actinide Compounds –

Molecular Magnetism of Neptunyl (+2) Complex NpO₂(C₆H₇O₂)₂(C₅H₅N)

Akio Nakamura¹, Masami Nakada¹, Tadahiro Nakamoto¹, Takafumi Kitazawa² and Masuo Takeda²

Magnetic property of a nitrogen (N)-coordinated neptunyl (+2) (Np(VI);5f¹) complex 1 NpO₂(acac)₂(py) (acac = C₆H₇O₂^2-, py = C₅H₅N) has been studied by ²³⁷Np Mössbauer and DC magnetization measurements, and is discussed with those of oxygen-coordinated neptunyl (+2) complex 2 NH₄[NpO₂(NO₃)₃]. The ²³⁷Np Mössbauer data showed that 1 exhibits typical paramagnetic-relaxation spectra at 11–40 K, similar to those of 2. While, the DC magnetization (M) data have revealed many striking features of 1 different from those of 2. First, its reciprocal magnetic susceptibility (1/χ) vs T(K) plots at 2–300 K showed a non-simple peculiar paramagnetic behavior shifting from a T-independent Van-Vleck type to a Curie-type with increasing field (H) from 0.002 to 5.5 T. Furthermore, at low temperature below ∼9 K, the isothermal M of the system exhibited anomalous relaxation behavior involving initial very large over-responsive M change and the subsequent gradual drift back to its `equilibrium' value (M_eq). Moreover, such M_eq of the system was often found to exhibit not-small run-to-run difference, very long-period slow variation in prolonged time scale, and strong perturbation effect from the SQUID-M measurement itself. Such novel magnetic features of 1 suggest the presence of largely metastable fluctuating magnetic (spin plus orbital) state in this supramolecule composed of individual Ising-type neptunyl (O=Np=O)⁺² molecular magnets.

URL: http://jpsj.ipap.jp/link?JPSJS/75S/146/
DOI: 10.1143/JPSJS.75S.146

References

1. N. N. Krot and D. N. Suglobov: Radiokhimiya 31 (1989) 1.
2. O. Kahn: Molecular Magnetism (Wiley-VCH, New York, 1993).
3. P. Rabu: J. Phys. Chem. Solids 65 (2004) 665 [CrossRef](Special Issue: Design, Characterization of Molecular-Based Magnetic Materials), and see many papers in this issue.
4. T. Nakamoto, M. Nakada, A. Nakamura, Y. Haga and Y. Ōnuki: Solid State Commun. 109 (1999) 77[CrossRef].
5. T. Nakamoto, M. Nakada and A. Nakamura: in Recent Research Developments in Inorganic Chemistry (Transworld Research Network, India, 2000) Vol. 2, p. 145.
6. T. Nakamoto, M. Nakada and A. Nakamura: Solid State Commun. 119 (2001) 523[CrossRef].
7. T. Nakamoto, M. Nakada and A. Nakamura: J. Nucl. Sci. Technol. 3 (2002) Suppl., p. 102.
8. J. Wang, T. Kitazawa, M. Nakada, T. Yamashita and M. Takeda: Bull. Chem. Soc. Jpn. 75 (2002) 253[CrossRef].
9. T. Kawasaki, T. Kitazawa, T. Nishimura, M. Nakada and M. Saeki: to be published in Hyperfine Interactions (ICAME Proc. 2005).
10. N. W. Alcock, D. J. Flanders and M. Pennington: Acta Crystallogr., Sect. C 43 (1987) 1476.