The observation of magnetization behavior of the nano-scale cluster magnet Mn12ac by 55Mn NMR

Kubo, Takeji; Koshiba, Takeshi; Goto, Takao; Akira, Oyamada; Fujii, Yutaka; Takeda, Kazuyoshi; Awaga, Kunio

doi:10.1016/s0921-4526(00)00666-9

Cited by 8 publications

(7 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…When the sample is already at T ≪ 1 K, the field-cooling procedure can be replaced by the application of a longitudinal field large enough to destroy the anisotropy barrier, e.g. B z = 8 T. Importantly, the shift of the 55 Mn NMR frequency with external field depends on the magnetization state of the sample: 50,53 in a ZFC sample each resonance line splits in two, one line moving to ω 0 + γ N B z and the other to ω 0 − γ N B z . Conversely, in a FC sample only one line is observed, shifting to higher or lower frequency depending on the direction of B z relative to the magnetization direction.…”

Section: Measurements and Data Analysismentioning

confidence: 99%

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

View full text Add to dashboard Cite

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.

show abstract

Section: Measurements and Data Analysismentioning

confidence: 99%

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

View full text Add to dashboard Cite

show abstract

“…This spin state is in the tetragonal crystal field doubly degenerate in the absence of an external magnetic field. The magnetization switching between the two degenerate mϭϮ10 states has been so far studied by susceptibility and magnetization 1-6 as well as proton 8 and 55 Mn NMR relaxation measurements. 9,10 It has been established that at low temperatures the magnetization reversal is exponential 1 following an initial short time recovery described by a square root of time ͱt behavior.…”

Section: Introductionmentioning

confidence: 99%

“…where is the magnetization switching time, 0 the inverse attempt frequency, the activation energy ⌬ represents the zero-field anisotropy induced barrier height for the ground state, [8][9][10][11] and B is the applied external magnetic field. Lowfield-low-temperature susceptibility measurements show that the relaxation time for magnetization reversal in zero external magnetic field is indeed given by an Arrhenious law ͓Eq.…”

Section: Introductionmentioning

confidence: 99%

“…͑1͒ for Sϭ10 and gϭ2. The regular dips in the magnetic-field dependence of below 2 K, 8,9 on the other hand, are due to resonant quantum tunneling of the magnetization between different levels having the same energy in the two wells.…”

Section: Introductionmentioning

confidence: 99%

“…The reason for this discrepancy is still unknown and further checks are necessary. There is also a difference between the values deduced from 55 Mn and 1 H NMR data, 8,9 which has been interpreted as arising from the different time regimes of the two sets of measurements.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

ac susceptibility and NMR observation of a deuterium isotope effect in the magnetization dynamics of theMn12-acetate nanomagnet

et al. 2003

View full text Add to dashboard Cite

The magnetization reversal dynamics of normal and deuterated Mn 12 -acetate nanomagnets has been studied above the blocking temperature T B ϭ2.7 K by ac magnetic susceptibility measurements between 100 Hz and 1 MHz and deuteron NMR relaxation. A pronounced isotope effect has been found which can be attributed to the changes in the strength of the hydrogen bonding of the water molecules on deuteration and the resulting changes in the spin-phonon coupling. Another point to be stressed is that the activation energy and relaxation rate obtained from our high-temperature-high-frequency magnetic susceptibility and deuteron NMR spinlattice relaxation data are significantly higher than the one obtained from the low-temperature-low-frequency magnetization switching data.

show abstract

Spectroscopy of Single-Molecule Magnets

McInnes¹

Structure and Bonding

View full text Add to dashboard Cite

The observation of magnetization behavior of the nano-scale cluster magnet Mn12ac by 55Mn NMR

Cited by 8 publications

References 16 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

ac susceptibility and NMR observation of a deuterium isotope effect in the magnetization dynamics of theMn12-acetate nanomagnet

Spectroscopy of Single-Molecule Magnets

Contact Info

Product

Resources

About