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Magnetic tunneling told to ignorants by two ignorants (2000)

Villain, J. ; Fort, A.

Springer

The European physical journal 17 (2000), S. 69-83

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ISSN: 1434-6036

Keywords: PACS. 75.45.+j Macroscopic quantum phenomena in magnetic systems - 75.50.Xx Molecular magnets - 61.46.+w Clusters, nanoparticles, and nanocrystalline materials

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract: Magnetic tunneling of a large spin subject to the Hamiltonian is investigated by elementary methods for weak fields H. In zero field (H=0) the tunnel frequency in the ground state is found to be equal to [0pt] multiplied by a quantity whose variation with s is slower than exponential. This result coincides with that of path integral methods [#!schi!#]. For the values of the longitudinal field which allow tunneling, the tunnel frequency is shown to vanish when H y =0 for certain “diabolic" values of [0pt] , in qualitative agreement with experiments by Wernsdorfer and Sessoli. The particular case H z =0 was already obtained by Garg by means of path integrals. The diabolic values of are in agreement with numerical results but, as already noticed by Wernsdorfer and Sessoli, they disagree with the experimental ones. This may be an effect of higher order anisotropy terms, which is briefly addressed in the conclusion.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100510070161

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Large Quadratic Hyperpolarizabilities with Donor-Acceptor Polyenes Exhibiting Optimum Bond Length Alternation: Correlation Between Structure and Hyperpolarizability (1997)

Blanchard-Desce, M. ; Alain, V. ; Bedworth, P. V. ; [et al.]

Weinheim : Wiley-Blackwell

Chemistry - A European Journal 3 (1997), S. 1091-1104

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ISSN: 0947-6539

Keywords: chromophores ; donor-acceptor systems ; hyperpolarizability ; nonlinear optics ; polyenes ; Chemistry ; General Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Donor-acceptor polyenes of various lengths, and that combine aromatic electron-donating moieties with powerful heterocyclic electron-withdrawing terminal groups, have been synthesized and characterized as efficient nonlinear optical (NLO) chromophores. Their linear and nonlinear optical properties have been investigated, and variations in these properties have been related to ground-state polarization (dipole μ) and structure. In particular, unprecedented quadratic hyperpolarizabilities (β) have been achieved (up to β(0) = 1500 × 10-30 esu) by reduction of the bond-length alternation (BLA) in the polyenic chain. In each series of homologous compounds, increasing the number n of conjugated double bonds in the polyenic chain results in a marked bathochromic shift, more pronounced BLA, and exponential increases in μβ(0) values. As a result, polyenic chromophores displaying excellent optical quadratic nonlinearities (μβ values as large as 100 times that of the quadratic NLO benchmark 4-dimethyl-amino-4′-nitrostilbene (DANS)), as well as satisfactory solubility, have been obtained.

Additional Material: 6 Ill.