NMR in oriented powder of Fe8 in zero and applied field

Baek, S.‐H.; Kawakami, S.; Furukawa, Yuji; Suh, B. J.; Borsa, F.; Kumagai, K.; Cornia, Andrea

doi:10.1016/j.jmmm.2003.12.062

Cited by 7 publications

(6 citation statements)

References 6 publications

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“…Previous 57 Fe NMR studies have yielded direct information on the local magnetic structure of the ground state and the hyperfine interactions. 29,30 In addition to the static effects mentioned above, 57 Fe NMR can provide precious information about the dynamic magnetic properties, including the tunneling effect, through the measurements of the relaxation rates as a function of temperature and external field, and by the temperature dependence of the resonance frequency in zero field, which are the subjects of the present investigation.…”

Section: Introductionmentioning

confidence: 99%

Fe57NMR and relaxation by strong collision in the tunneling regime in the molecular nanomagnet Fe8

et al. 2005

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Fe NMR measurements have been performed in single crystal and oriented powder of enriched 57 Fe8 molecular cluster in the temperature range 0.05-1.7 K in zero external field and with small perturbing field up to 1 T for both transverse and longitudinal orientation of H with respect to the anisotropy axis. The 57 Fe NMR spectrum is analyzed in terms of a dominant contribution due to the hyperfine interaction arising from core polarization. The measured temperature dependence of the resonance frequency is explained well by calculating the local average magnetic moment of the Fe 3+ ion with a simple model which incorporates the effects of thermal average in the low lying energy states. Nuclear spin-lattice relaxation rate ͑1/T 1 ͒ and spin-spin relaxation rate ͑1/T 2 ͒ were investigated via temperature and field dependences. The obtained results are analyzed in terms of both intrawell thermal fluctuations of the hyperfine fields due to spin-phonon interaction, and interwell fluctuations due to phonon assisted quantum tunneling of the magnetization. It is argued that in zero external field and at low T the 57 Fe and the proton 1 / T 1 is dominated by a strong collision relaxation mechanism due to the fact that phonon assisted tunneling transitions generate a sudden reversal of the local quantization field at the nuclear site. The data could be explained satisfactorily by assuming that the 57 Fe 1 / T 1 measures directly the effective tunneling rate. However, in order to fit the data we had to assume a larger in-plane anisotropy than previously reported, resulting in a bigger tunneling splitting in zero field. A comparison with published data of 55 Mn in Mn12 indicates that a strong collision relaxation mechanism may apply also in Mn12. Finally the H and T dependence of 57 Fe 1 / T 2 is well explained simply in terms of thermal fluctuations of the magnetization without any tunneling contribution. At very low T the 1 / T 2 approaches a limiting value which can be explained in terms of the dipolar interaction between proton and 57 Fe nuclei in the quasistatic regime.

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Section: Introductionmentioning

confidence: 99%

Fe57NMR and relaxation by strong collision in the tunneling regime in the molecular nanomagnet Fe8

et al. 2005

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“…Elsewhere we will report evidence that the same description appears to apply for the giant Keplerate magnetic molecule {Mo72Fe30} where 30 Fe 3+ ions occupy the sites of an icosidodecahedron and the ground state is a non-degenerate S = 0 state [4], On the other hand, for the magnetic molecule V12, (a 3-dimensional cluster, but the predominant exchange pathways link a central group of four spins s = 1/2) there is no evidence of a peak in 1/Ti at low T [141]. It is therefore certain that scaling behavior of the spin-lattice relaxation rate is by no means universal for magnetic molecules.…”

Section: Resultsmentioning

confidence: 76%

“…The only drawback is that the strong coupling makes the NMR signal detectable only in a narrow temperature range. Previous ^Fe NMR studies have yielded direct information on the local magnetic structure of the ground state and the hyperfine in teractions [40,41]. In addition to the static effects mentioned above, 57 Fe NMR can provide precious information about the dynamic magnetic properties, including the tunneling effect, through the measurements of the relaxation rates as a function of temperature and external field, and by the temperature dependence of the resonance frequency in zero field, which are the subjects of the present investigation.…”

Section: Introductionmentioning

confidence: 87%

“…SMMs are exchange coupled clusters, at present, of two to thirty paramagnetic ions (e.g., iron dimer [3] to a giant cluster Fe3Q [4]), usually from the first period of the transition metals. 1 The magnetic centers in the molecule are fairly well shielded (i.e., very weak intermolecuiar interaction) by large organic ligand shells, and thus the individual molecules are magnetically almost independent.…”

Section: Single Molecule Magnets (Smms)mentioning

confidence: 99%

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Spin dynamics and quantum tunneling in Fe8 nanomagnet and in AFM rings by NMR

Baek

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“…For example, in ID Heisenberg magnetic chains, the long-time persistence of spin correlation has dramatic consequences on the field dependence of 1/Ti [37,38]. Secondly, NMR spectrum gives us information on the hyperfine interactions of the nuclei with the local magnetic moments, and its held dependence provides information of the internal magnetic structure [39][40][41][42]. Thirdly, NMR is a powerful tool for the investigation of quantum tunneling effect [43,44].…”

Section: Nuclear Magnetic Resonance As a Tool To Investigate Smmsmentioning

confidence: 99%

Spin dynamics and quantum tunneling in Fe8 nanomagnet and in AFM rings by NMR

Baek

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NMR in oriented powder of Fe8 in zero and applied field

Cited by 7 publications

References 6 publications

Fe57NMR and relaxation by strong collision in the tunneling regime in the molecular nanomagnet Fe8

Fe57NMR and relaxation by strong collision in the tunneling regime in the molecular nanomagnet Fe8

Spin dynamics and quantum tunneling in Fe8 nanomagnet and in AFM rings by NMR

Spin dynamics and quantum tunneling in Fe8 nanomagnet and in AFM rings by NMR

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