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The disentangling of hysteretic spin transition, polymorphism and metastability in bistable thin films formed by sublimation of bis(scorpionate) Fe(II) molecules

Abstract

We investigate the size-dependent bistability of a FeII[HB(3,5-(Me)2Pz)3]2 spin-transition compound in the form of thin films, the thickness of which varies from 130 to 8500 nm. From combined structural, magnetic and optical measurements, we demonstrate that the materials prepared by sublimation consist in crystalline grains of the triclinic phase exhibiting the first-order spin transition coexisting with those of a new high-spin metastable tetragonal polymorph in a quite large proportion (ca. 42%). Accordingly, we show that the as-sublimed thin-film of a 130 nm thickness retains a remarkable 17 K width hysteresis (T1/2 = 152 K) while the spin transition becomes quantitative by the thermal annealing of the metastable phase at 373 K. Consistently with the calorimetric data, the structural analysis based on single-crystal x-ray diffraction measurements provides evidences for a thermal hysteresis resulting from successive crystallographic phase transitions, which account for the asymmetric shape of hysteresis and the variation of cooperativity observed in the magnetic and optical data and that, whatever the material dimension.

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Publication details

The article was received on 21 Jul 2017, accepted on 01 Oct 2017 and first published on 02 Oct 2017


Article type: Paper
DOI: 10.1039/C7TC03276E
Citation: J. Mater. Chem. C, 2017, Accepted Manuscript
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    The disentangling of hysteretic spin transition, polymorphism and metastability in bistable thin films formed by sublimation of bis(scorpionate) Fe(II) molecules

    O. Iasco, M. Boillot, A. Bellec, R. Guillot, E. Riviere, S. Mazerat, S. Nowak, D. Morineau, A. Brosseau, F. Miserque, V. Repain and T. Mallah, J. Mater. Chem. C, 2017, Accepted Manuscript , DOI: 10.1039/C7TC03276E

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