55Mn NMR and relaxation studies on Mn12-acetate

Goto, Takao; Kubo, Takeji; Koshiba, Takeshi; Fujii, Yutaka; Akira, Oyamada; Arai, Junichi; Takeda, Keiki; Awaga, Kunio

doi:10.1016/s0921-4526(99)02478-3

Cited by 26 publications

(24 citation statements)

References 2 publications

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“…We found instead the avalanches at |B (av) z | ≃ 1.9 T, i.e., the fourth level crossing, m = ±10 ↔ ∓6, but our measurements are done at T ≃ 30 mK. Goto et al 69 also reported the observation of magnetic avalanches in Mn 12 -ac, and studied the temperature dependence of the avalanche field B (av) z . Their finding that B (av) z increases with temperature was interpreted as a sign that the avalanches occur more easily when the thermal contact to the bath is weaker.…”

Section: B Longitudinal Field Sweeps and Magnetic Avalanchesmentioning

confidence: 76%

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnetMn12−ac: Test for the theory of spin tunneling

Morello

Jongh

2007

Phys. Rev. B

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The description of the tunneling of a macroscopic variable in the presence of a bath of localized spins is a subject of great fundamental and practical interest, and is relevant for many solid-state qubit designs. Most of the attention is usually given to the dynamics of the "central spin" (i.e., the qubit), while little is known about the spin bath itself. Here we present a detailed study of the dynamics of the nuclear spin bath in the Mn12-ac single-molecule magnet, probed by NMR experiments down to very low temperatures (T ≃ 20 mK). The results are critically analyzed in the framework of the Prokof'ev-Stamp theory of nuclear-spin mediated quantum tunneling. We find that the longitudinal relaxation rate of the 55 Mn nuclei in Mn12-ac becomes roughly T -independent below T ≃ 0.8 K, and can be strongly suppressed with a longitudinal magnetic field. This is consistent with the nuclear relaxation being caused by quantum tunneling of the molecular spin, and we attribute the tunneling fluctuations to the minority of fast-relaxing molecules present in the sample. The transverse nuclear relaxation is also T -independent for T < 0.8 K, and can be explained qualitatively and quantitatively by the dipolar coupling between like nuclei in neighboring molecules. This intercluster nuclear spin diffusion mechanism is an essential ingredient for the global relaxation of the nuclear spin bath. We also show that the isotopic substitution of 1 H by 2 H leads to a slower nuclear longitudinal relaxation, consistent with the decreased tunneling probability of the molecular spin. Finally, we demonstrate that, even at the lowest temperatures -where only T -independent quantum tunneling fluctuations are present -the nuclear spins remain in thermal equilibrium with the lattice phonons, and we investigate the timescale for their thermal equilibration. After a review of the theory of macroscopic spin tunneling in the presence of a spin bath, we argue that most of our experimental results are consistent with that theory, but the thermalization of the nuclear spins is not. This calls for an extension of the spin bath theory to include the effect of spin-phonon couplings in the nuclear-spin mediated tunneling process.

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Section: B Longitudinal Field Sweeps and Magnetic Avalanchesmentioning

confidence: 76%

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnetMn12−ac: Test for the theory of spin tunneling

Morello

Jongh

2007

Phys. Rev. B

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“…Helium temperatures. 15 In the recent paper, we have determined the hyperfine interaction tensors of 55 Mn nuclei in Mn 12 Ac by analyzing the more detailed 55 Mn NMR spectra on the basis of the ground-state spin-configuration. 16 In the present work, we have measured, using oriented powder sample, the transverse relaxation time T 2 and the spin-lattice relaxation time T 1 of 55 Mn in Mn 12 Ac.…”

Section: Introductionmentioning

confidence: 99%

Transverse and longitudinal relaxations of55Mnin the molecular cluster magnetMn12
Goto
¹
,
Koshiba
²
,
Kubo
³

et al. 2003
Phys. Rev. B
Self Cite
29
1
35
2
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The nuclear magnetic relaxation times T2 and T1 of 55 Mn in the molecular cluster magnet Mn12 Ac have been measured, using the spin-echo method for oriented powder sample, at low temperatures below 2.5 K down to 200 mK in the fields up to 9 T applied along the c-axis. Above about 1.5 K both of relaxation rates T −1 were also interpreted reasonably in terms of the above theoretical treatment. The quantitative comparison between the experimental results and the theoretical equations was made using hyperfine interaction tensors for each of three manganese ions determined from the analysis for the NMR spectra in zero field.

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“…Because of the implied overlap of the wavefunctions of the magnetization vector across the double-well, it has been recently suggested that Mn 12 -Ac could form the basis of a quantum bit [6]. Mn 12 -Ac has thus been well investigated by essentially all available techniques, including magnetization measurements of a.c. and d.c. susceptibility [4,5,7,8], electron paramagnetic resonance (EPR) [9-13], Raman spectroscopy [14,15], NMR [16][17][18][19][20][21], specific heat [22], infrared and optical techniques [23][24][25], neutron scattering [26,27], conductivity [28] and micro-Hall [28]. We here report a simple EPR-based method of measuring the surface magnetization or, equivalently, effective magnetic fields near an Mn 12 -Ac crystal.…”

Section: Introductionmentioning

confidence: 99%

Probing magnetic fields on crystals of the nanomagnet Mn12-acetate by electron paramagnetic resonance

Rakvin

Žilić

North

et al. 2003

Journal of Magnetic Resonance

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55Mn NMR and relaxation studies on Mn12-acetate

Cited by 26 publications

References 2 publications

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnetMn12−ac: Test for the theory of spin tunneling

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnetMn12−ac: Test for the theory of spin tunneling

Transverse and longitudinal relaxations of55Mnin the molecular cluster magnetMn12
Goto
¹
,
Koshiba
²
,
Kubo
³

et al. 2003
Phys. Rev. B
Self Cite
29
1
35
2
View full text Add to dashboard Cite

Probing magnetic fields on crystals of the nanomagnet Mn12-acetate by electron paramagnetic resonance

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55Mn NMR and relaxation studies on Mn12-acetate

Cited by 26 publications

References 2 publications

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnetMn12−ac: Test for the theory of spin tunneling

Dynamics and thermalization of the nuclear spin bath in the single-molecule magnetMn12−ac: Test for the theory of spin tunneling

Transverse and longitudinal relaxations of55Mnin the molecular cluster magnetMn12Goto1, Koshiba2, Kubo3 et al. 2003Phys. Rev. BSelf Cite291352View full textAdd to dashboardCite

Probing magnetic fields on crystals of the nanomagnet Mn12-acetate by electron paramagnetic resonance

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Transverse and longitudinal relaxations of55Mnin the molecular cluster magnetMn12
Goto
¹
,
Koshiba
²
,
Kubo
³

et al. 2003
Phys. Rev. B
Self Cite
29
1
35
2
View full text Add to dashboard Cite