The origin of the second relaxation process in the [Mn12O12(O2CR)16(H2O)4] single-molecule magnets: ‘Jahn–Teller isomerism’ in the [Mn12O12] core

Sun, Zheng; Ruiz, D. E.; Hendrickson, David N.; Dilley, N. R.; Maple, M. B.; Soler, Mónica; Folting, Kirsten; Christou, George; Ribas, Joan

doi:10.1039/a906451f

Cited by 109 publications

(87 citation statements)

References 12 publications

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“…Based on this, we are forced to assume that tunneling takes place only in a small minority of the clusters, and that some additional mechanism takes care of the relaxation of the nuclei in molecules that do not tunnel. This is a very realistic assumption, since all samples of Mn 12 -ac are reported to contain a fraction of FRMs, 45,46 as mentioned in Sect. II A.…”

Section: B Longitudinal Spin Relaxation In Zero Fieldmentioning

confidence: 99%

“…clusters characterized by a lower anisotropy barrier and a much faster relaxation rate, as observed for instance by ac-susceptibility 44 and magnetization measurements. 45 It has been recognized that such FRMs originate from Jahn-Teller isomerism, 46 i.e. the presence in the molecule of one or two Mn 3+ sites where the elongated Jahn-Teller axis points in a direction roughly perpendicular instead of parallel to the crystallineĉ-axis.…”

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confidence: 99%

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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 Spin Relaxation In Zero Fieldmentioning

confidence: 99%

mentioning

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

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“…3(d)]. The interpretation of the experiments on Mn 12 -ac is slightly complicated by the fact that this particular compound contains a minority of fast-relaxing molecules [40,47] which remain dynamic down to the lowest temperatures, whereas the majority species have a negligibly small tunneling rate in zero field. On the other hand, the fact that a large fraction of the sample can remain fully magnetized for long times (months), has allowed to measure the nuclear dynamics in Mn 12 -ac as a function of the sample magnetization, and revealed the effect of dipolar coupling between nuclear spins (i.e.…”

Section: Resultsmentioning

confidence: 99%

Quantum Nanomagnets and Nuclear Spins: An Overview

Morello¹

2008

NATO Science for Peace and Security Series B: Physics and Biophysics

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“…In all cases where the FR species are obtained in single-crystal form, X-ray studies show that one or more of the Jahn-Teller (JT) elongation axes associated with the Mn III atoms are abnormally oriented 18,19,21,24,25,33 in comparison to the usual SR form of Mn 12 . 26,27,[34][35][36][37] This is illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the spacing between the QMT steps associated with the FR species (~0.4 T) is not all that dissimilar to those of the SR species (~0.45 T), suggesting that they possess similar uniaxial anisotropy constants D. [14][15][16] Subsequently, detailed synthetic work by Christou, Hendrickson and co-workers, involving ligand substitution and crystallization from a variety of solvents, resulted in the discovery of many different forms of Mn 12 possessing essentially the same neutral Mn 12 O 12 core. 11,12,[17][18][19][20][21][22][23][24][25][26][27] However, important differences have been inferred from X-ray and magnetic studies. Most notably, the various Mn 12 complexes can be grouped broadly into two categories, i.e.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

2009

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A novel angle-swept high-frequency electron paramagnetic resonance (HFEPR) technique is described that facilitates efficient in-situ alignment of single-crystal samples containing lowsymmetry magnetic species such as single-molecule magnets (SMMs). This cavity-based technique involves recording HFEPR spectra at fixed frequency and field, while sweeping the applied field orientation. The method is applied to the study of a low-symmetry Jahn-Teller variant of the extensively studied spin S = 10 Mn 12 SMMs (e.g. Mn 12 -acetate). The lowsymmetry complex also exhibits SMM behavior, but with a significantly reduced effective

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The origin of the second relaxation process in the [Mn12O12(O2CR)16(H2O)4] single-molecule magnets: ‘Jahn–Teller isomerism’ in the [Mn12O12] core

Cited by 109 publications

References 12 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

Quantum Nanomagnets and Nuclear Spins: An Overview

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

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