ac susceptibility and NMR observation of a deuterium isotope effect in the magnetization dynamics of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Mn</mml:mi></mml:mrow><mml:mrow><mml:mn>12</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>-acetate nanomagnet

Blinc, R.; Zalar, Boštjan; Gregorovič, A.; Arčon, Denis; Kutnjak, Zdravko; Filipič, C.; Levstik, A.; Achey, R. M.; Dalal, Naresh S.

doi:10.1103/physrevb.67.094401

Cited by 21 publications

(13 citation statements)

References 21 publications

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“…For this reason, one can often find significant variations in U ef f values throughout the literature. [36][37][38] As we shall show here, part of the reason is due to the non-Arrhenius behavior observed in Fig. 3.…”

Section: A Ac Susceptibilitymentioning

confidence: 74%

Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets

Redler

Lampropoulos²,

Datta³

et al. 2009

Phys. Rev. B

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High-frequency electron paramagnetic resonance ͑HFEPR͒ and alternating current ͑ac͒ susceptibility measurements are reported for a new high-symmetry Mn 12 OH complexes. These comparisons reveal important insights into the factors that influence the values of the effective barrier to magnetization reversal, U ef f , deduced on the basis of ac susceptibility measurements. In particular, we find that variations in U ef f can be correlated with the degree of disorder in a crystal which can be controlled by desolvating ͑drying͒ samples. This highlights the importance of careful sample handling when making measurements on SMM crystals containing volatile lattice solvents. The HFEPR data additionally provide spectroscopic evidence suggesting that the relatively weak disorder induced by desolvation influences the quantum tunneling interactions and that it is under-barrier tunneling that is responsible for a consistent reduction in U ef f that is found upon drying samples. Meanwhile, the axial anisotropy deduced from HFEPR is found to be virtually identical for all four Mn 12 complexes, with no measurable reduction upon desolvation.

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Section: A Ac Susceptibilitymentioning

confidence: 74%

Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets

Redler

Lampropoulos²,

Datta³

et al. 2009

Phys. Rev. B

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“…This conjecture is supported by earlier observations that hydrogen bonding must be important to the magnetization dynamics in the Mn 12 cluster because deuteration leads to a significant slowing down of the magnetization reversal dynamics as measured by high-frequency ac susceptibility. 46 We note also that all of the unusual solvent-induced anomalies reported in this paper for Mn 12 -ac are absent in the EPR spectra for a related high-symmetry ͑S 4 ͒ Mn 12 complex ͓Mn 12 O 12 ͑O 2 CCH 2 Br͒ 16 ͑H 2 O͒ 4 ͔ ·4CH 2 Cl 2 which possesses a full compliment of four CH 2 Cl 2 solvent molecules per Mn 12 , and none of the low symmetry hydrogen bonding environments present in Cornia's model. 26 FIG.…”

Section: Discussionmentioning

confidence: 99%

Discrete easy-axis tilting inMn12-acetate, as determined by EPR: Implications for the magnetic quantum tunneling mechanism

et al. 2004

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The variation with microwave frequency and temperature of previously reported anomalous peaks in the EPR spectra of Mn 12 -acetate, under large transverse fields, reveals that the molecular easy magnetization axes are tilted with respect to the global symmetry direction. More importantly, on the basis of the angle dependence of fine structures observed in the EPR spectra we infer that the tilt distribution must be discrete, as was previously suspected from studies which demonstrated the presence of a locally varying rhombic anisotropy [S. Hill et al., Phys. Rev. Lett. 90, 217204 (2003)]. The tilts are confined to two orthogonal planes, and the distribution extends up to ϳ1.7°degrees away from the global easy ͑z͒ axis. We ascribe the tilting to the hydrogen-bonding effect associated with the disordered acetic acid solvent molecules. The effect is considerably larger than deduced from x-ray diffraction analyses. These data constitute the sought-after evidence for the presence of transverse fields in Mn 12 -acetate, and provide a possible explanation for the lack of selection rules in the resonant quantum tunneling behavior seen in low-temperature hysteresis experiments for this S =10 system.

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“…[7,8] Herein, we show that non-linear Arrhenius behavior is evident even for data collected in the more typical frequency (u) range (5-1500 Hz), and that the apparent U eff obtained is thus distinctly dependent on the range of data constrained to a linear fit to the Arrhenius equation, giving erroneously large apparent U eff values. This conclusion is supported by comparisons of U eff values with those from high-frequency EPR (HFEPR) data (U EPR ).…”

mentioning

confidence: 91%

A Caveat for Single‐Molecule Magnetism: Non‐linear Arrhenius Plots

2009

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Single-molecule magnets (SMMs) are molecules that, below a certain temperature (T B ), function as individual nanoscale magnetic particles, exhibiting magnetization hysteresis loops.[1] As such, they represent an alternative and molecular (bottom-up) route to nanomagnetism, complementing the top-down approach to traditional magnetic nanomaterials.[2] SMMs also exhibit fascinating quantum behavior such as quantum tunneling of the magnetization (QTM) [3] and quantum phase interference (QPI), [4] showing that they are truly mesoscale entities straddling the classical/quantum divide. The barrier causing slow magnetization relaxation arises from a combination of a large ground-state spin (S) and easy-axis anisotropy (negative zerofield splitting parameter, D). The most studied SMMs are the 4 ] family with S = 10 ground states, and their derivatives, [5] while in recent years others have been discovered.[6] Alternating current (ac) magnetic susceptibility studies are a convenient method of assessing whether a compound might be an SMM; frequency-dependent out-of-phase (c'' M ) signals are indicative of the superparamagnet-like properties of an SMM. The variation in signal position with ac frequency can then be used as a source of rate vs T kinetic data, because the c'' M peak maximum is the temperature at which the angular frequency of the oscillating field equals the rate (1/t, where t is the relaxation lifetime) of spin vector reversal. This allows construction of a lnA C H T U N G T R E N N U N G (1/t) vs 1/T plot based on the Arrhenius relationship given in Equation (1), the behavior expected of a thermally-activated process over a single barrier:From the slope of the straight line can be obtained the effective barrier to relaxation (U eff ), and from the intercept the pre-exponential term (1/t 0 ). Adherence to the Arrhenius relationship has been a defining property of a SMM, reflecting the low-dimensional origin of its magnetic properties rather than 3D interactions and long-range magnetic order. Deviations

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

Cited by 21 publications

References 21 publications

Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets

Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets

Discrete easy-axis tilting inMn12-acetate, as determined by EPR: Implications for the magnetic quantum tunneling mechanism

A Caveat for Single‐Molecule Magnetism: Non‐linear Arrhenius Plots

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