Macroscopic quantum tunnelling and hysteresis loops of mesoscopic magnets

Dobrovitski, V. V.; Zvezdin, A. K.

doi:10.1209/epl/i1997-00254-x

Cited by 91 publications

(64 citation statements)

References 15 publications

(27 reference statements)

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“…[2][3][4] On the other hand, quantum dynamical calculations of the change of the magnetization due to a slowly reversing applied field have shown that nonadiabatic transitions between energy levels govern the magnetization dynamics and that the tunneling of the magnetization at Hϭ0 can be modeled by the Landau-Zener mechanism. [5][6][7][8] In view of the generic character of the findings of Refs. 2-6, it appears logical to search for a unified description of the quantum dynamics of the magnetization at zero temperature.…”

Section: Introductionmentioning

confidence: 96%

Theory of quantum tunneling of the magnetization in magnetic particles

et al. 1997

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Theory of quantum tunneling of the magnetization in magnetic particles de Raedt, Hans; Miyashita, S.; Saito, K.; García-Pablos, D.; García, N. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We study the response of the magnetization to a time-dependent applied magnetic field H(t) in a model for a uniaxial magnet. It is shown that a staircase structure in the magnetization curve results from Landau-Zener tunneling between different pairs of nearly-degenerate energy levels. This mechanism might be relevant to the analysis of the hysteresis of nanoscale magnets at low temperatures, allowing one to extract the energy splittings from the hysteresis curve. We investigate the dependence of the staircase structure on the sweep rate dH(t)/dt, and point out some universal features of the staircase in uniaxial magnets. We also study the effect of a step-wise ͑instead of continuous͒ increase in the field, and show that the size of the steps depends sensitively on the procedure used to change the applied field. ͓S0163-1829͑97͒06042-6͔

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Section: Introductionmentioning

confidence: 96%

Theory of quantum tunneling of the magnetization in magnetic particles

et al. 1997

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“…Indeed, each of these effects have been discussed in MQT literature, e.g. dipolar fields [39], distributed crystal field parameters caused by dislocations [40], thermally assisted tunneling [14,41,42], the Landau-Zener effect [43,44,45], and hyperfine interactions [46,47]. Based on our recent theoretical work [37], we find that a distribution in the uniaxial crystal field parameter, so called D−strain, contributes significantly to the EPR linewidths for the Fe 8 Br and Mn 12 −ac systems.…”

Section: Introductionmentioning

confidence: 99%

Detailed single-crystal EPR line shape measurements for the single-molecule magnetsFe8BrandMn
Hill
¹
,
Maccagnano
²
,
Park
³

et al. 2002
Phys. Rev. B
118
8
77
1
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It is shown that our multi-high-frequency (40 − 200 GHz) resonant cavity technique yields distortion-free high field EPR spectra for single crystal samples of the uniaxial and biaxial spin S = 10 single molecule magnets (SMMs) The observed lineshapes exhibit a pronounced dependence on temperature, magnetic field, and the spin quantum numbers (M S values) associated with the levels involved in the transitions.Measurements at many frequencies allow us to separate various contributions to the EPR linewidths, including significant D−strain, g−strain and broadening due to the random dipolar fields of neighboring molecules. We also identify asymmetry in some of the EPR lineshapes for Fe 8 , and a previously unobserved fine structure to some of the EPR lines for both the Fe 8 and Mn 12 systems. These findings prove relevant to the mechanism of quantum tunneling of magnetization in these SMMs.

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“…For the ground-state tunneling, the theory of such process has been developed along the lines of the Landau-Zener effect. 36,37,38,39,40,41 A nice feature of the field-sweep approach is that the fraction of molecules that change the direction of the spin depends on the tunneling level splitting and on the sweep rate but is insensitive to the dissipation in the experimental limit of small splitting.…”

Section: Introductionmentioning

confidence: 99%

Dislocation-induced spin tunneling inMn12acetate

Garanin

Chudnovsky

2002

Phys. Rev. B

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Comprehensive theory of quantum spin relaxation in Mn12 acetate crystals is developed, that takes into account imperfections of the crystal structure and is based upon the generalization of the LandauZener effect for incoherent tunneling from excited energy levels. It is shown that linear dislocations at plausible concentrations provide the transverse anisotropy which is the main source of tunneling in Mn12. Local rotations of the easy axis due to dislocations result in a transverse magnetic field generated by the field applied along the c-axis of the crystal, which explains the presence of odd tunneling resonances. Long-range deformations due to dislocations produce a broad distribution of tunnel splittings. The theory predicts that at subkelvin temperatures the relaxation curves for different tunneling resonances can be scaled onto a single master curve. The magnetic relaxation in the thermally activated regime follows the stretched-exponential law with the exponent depending on the field, temperature, and concentration of defects.

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Macroscopic quantum tunnelling and hysteresis loops of mesoscopic magnets

Cited by 91 publications

References 15 publications

Theory of quantum tunneling of the magnetization in magnetic particles

Theory of quantum tunneling of the magnetization in magnetic particles

Detailed single-crystal EPR line shape measurements for the single-molecule magnetsFe8BrandMn
Hill
¹
,
Maccagnano
²
,
Park
³

et al. 2002
Phys. Rev. B
118
8
77
1
View full text Add to dashboard Cite

Dislocation-induced spin tunneling inMn12acetate

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Macroscopic quantum tunnelling and hysteresis loops of mesoscopic magnets

Cited by 91 publications

References 15 publications

Theory of quantum tunneling of the magnetization in magnetic particles

Theory of quantum tunneling of the magnetization in magnetic particles

Detailed single-crystal EPR line shape measurements for the single-molecule magnetsFe8BrandMnHill1, Maccagnano2, Park3 et al. 2002Phys. Rev. B1188771View full textAdd to dashboardCite

Dislocation-induced spin tunneling inMn12acetate

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About

Detailed single-crystal EPR line shape measurements for the single-molecule magnetsFe8BrandMn
Hill
¹
,
Maccagnano
²
,
Park
³

et al. 2002
Phys. Rev. B
118
8
77
1
View full text Add to dashboard Cite