Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 18: Correlated Electrons: Low-dimensional Systems - Materials 2

TT 18.13: Talk

Tuesday, February 26, 2008, 18:30–18:45, H 2053

Microscopic simulation and analysis of a spin crossover transition — •Harald O. Jeschke¹, L. Andrea Salguero¹, Badiur Rahaman², Christian Buchsbaum³, Volodymyr Pashchenko³, Martin U. Schmidt³, Tanusri Saha-Dasgupta², and Roser Valenti¹ — ¹Institut für Theoretische Physik, Universität Frankfurt, Max-von-Laue-Str. 1, 60438 Frankfurt, Germany — ²S.N. Bose National Centre for Basic Sciences, JD Block, Sector 3, Salt Lake City, Kolkata 700098, India — ³Institut für Anorganische und Analytische Chemie, Universität Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt, Germany

In spin crossover materials, an abrupt phase transition between a low spin state and a high spin state can be driven by temperature, pressure or illumination. Of a special relevance are Fe(II) based coordination polymers where, in contrast to molecular systems, the phase transition shows a pronounced hysteresis which is desirable for technical applications. A satisfactory microscopic explanation of this large cooperative phenomenon has been sought for a long time. The lack of X-ray data has been one of the reasons for the absence of microscopic studies. In this work, we present an efficient route to prepare reliable model structures and within ab initio density functional theory analysis and effective model considerations we show that in polymeric spin crossover compounds magnetic exchange between high spin Fe(II) centres is as important as elastic couplings for explaining the considerable cooperativity and thus the width of the hysteresis.