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Slow relaxation in a one-dimensional rational assembly of antiferromagnetically-coupled [Mn4] single-molecule-magnets

L. Lecren·O. Roubeau·C. Coulon·Yang-Guang Li·X. Le Goff·W. Wernsdorfer·H. Miyasaka·R. Clerac
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Abstract

Four discrete MnIII/MnII tetra-nuclear complexes with double-cuboidal core were synthesized. dc magnetic measurements show that both Mn2+ - Mn3+ and Mn3+ - Mn3+ magnetic interactions are ferromagnetic in three samples leading to an S = 9 ground state for the Mn4 unit. Furthermore, these complexes are Single-Molecule Magnets (SMMs) clearly showing both thermally activated and ground state tunneling regimes. Slight changes in the [Mn4] core geometry result in an S = 1 ground state in fourth sample. A one-dimensional assembly of [Mn4] units was obtained in the same synthetic conditions with the subsequent addition of NaN3. Double chair-like N3- bridges connect identical [Mn4] units into a chain arrangement. This material behaves as an Ising assembly of S = 9 tetramers weakly antiferromagnetically coupled. Slow relaxation of the magnetization is observed at low temperature for the first time in an antiferromagnetic chain, following an activated behavior with 47 K and tau_0 = 7x10^-11 s. The observation of this original thermally activated relaxation process is induced by finite-size effects and in particular by the non-compensation of spins in segments of odd-number units. Generalizing the known theories on the dynamic properties of poly-disperse finite segments of antiferromagnetically coupled Ising spins, the theoretical expression of the characteristic energy gaps were estimated and successfully compared to the experimental values.

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L. Lecren, O. Roubeau, C. Coulon, Yang-Guang Li, X. Le Goff, W. Wernsdorfer, H. Miyasaka, R. Clerac. 2005-11-07. Slow relaxation in a one-dimensional rational assembly of antiferromagnetically-coupled [Mn4] single-molecule-magnets. https://arxiv.org/abs/cond-mat/0511170

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