The propagation of the thermal spin transition of [Fe(btr)2(NCS)2]·H2O single crystals, observed by optical microscopy

François Varret; Ahmed Slimani; Kamel Boukheddaden; Christian Chong; Haritosh Mishra; Eric Collet; Jaap Haasnoot; Sébastien Pillet

doi:10.1039/C1NJ20332K

The propagation of the thermal spin transition of [Fe(btr)₂(NCS)₂]·H₂O single crystals, observed by optical microscopy†‡

François Varret,^a Ahmed Slimani,*^a Kamel Boukheddaden,*^a Christian Chong,^a Haritosh Mishra,^a Eric Collet,^b Jaap Haasnoot^c and Sébastien Pillet^d

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* Corresponding authors

^a Groupe d'Etude de la Matière Condensée, CNRS-Université UMR 8635, 45 avenue des Etats-Unis, 78035 Versailles, France
E-mail: francois.varret@physique.uvsq.fr, slimani@physique.uvsq.fr

^b Institut de Physique de Rennes, UMR 6251 Université Rennes 1-CNRS, campus de Beaulieu, 35042 Rennes, France

^c Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P. O. Box 9502, 2300 RA Leiden, The Netherlands

^d Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, UMR CNRS 7036, Institut Jean Barriol, Nancy-Université, BP239, 54506 Vandoeuvre les Nancy, France

Abstract

We observed by optical microscopy the propagation of the thermal spin transition in single crystals of the archetype compound [Fe(btr)₂(NCS)₂]·H₂O (btr = 4,4′-bis-1,2,4-triazole). In fresh crystals we could follow well-defined transformation fronts of various shapes. The propagation conditions revealed to depend very sensitively on the structural quality of the crystals. The best observations were obtained on cooling selected fresh crystals, rather thin, protected by an oil layer, under isothermal conditions. They evidenced the progression of a well-defined transformation front through the entire crystal. This is typical for a nucleation and growth process governed by inhomogeneous nucleation. The front shape was simple (circular or linear) and progression was regular in the best cases. Crystals of lesser quality (or already cycled through the transition) exhibited a more complex behaviour, assigned to the impact of internal stresses, either genuine or generated by the previous transformation of the crystals. These observations provide new insights into the physics of like-spin domains, which are briefly discussed.

This article is part of the themed collection: In honour of Didier Astruc

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Article information

DOI: https://doi.org/10.1039/C1NJ20332K
Article type: Paper
Submitted: 14 Apr 2011
Accepted: 01 Jul 2011
First published: 22 Jul 2011

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New J. Chem., 2011,35, 2333-2340

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The propagation of the thermal spin transition of [Fe(btr)₂(NCS)₂]·H₂O single crystals, observed by optical microscopy

F. Varret, A. Slimani, K. Boukheddaden, C. Chong, H. Mishra, E. Collet, J. Haasnoot and S. Pillet, New J. Chem., 2011, 35, 2333 DOI: 10.1039/C1NJ20332K

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