Pressure-induced two-step spin transition with structural symmetry breaking: X-ray diffraction, magnetic, and Raman studies

Helena Shepherd (1, 2, 3) , Sylvestre Bonnet (4) , Philippe Guionneau (2) , Salma Bedoui (3) , Gastón Garbarino (5) , William Nicolazzi (3) , Azzedine Bousseksou (3) , Gábor Molnár (3)

1 Department of Chemistry
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
3 LCC - Laboratoire de chimie de coordination
4 Leiden Institute of Chemistry
5 ESRF - European Synchrotron Radiation Facility

We have used single-crystal x-ray diffraction, Raman spectroscopy, and magnetometry to investigate the effect of hydrostatic pressures up to 16 kbar on the molecular spin crossover complex [Fe^II(bapbpy)(NCS)₂]. A stepped first-order transition from the high-spin (HS) to low-spin (LS) phase was observed upon compression of single-crystal samples. The intermediate phase (IP) is stable between 4 and 11 kbar at room temperature. This phase is characterized by supercell reflections and tripling of the c-axis of the unit cell (C2/c) due to the formation of a periodic [HS-LS-LS] structural motif, as seen in the thermal stepped transition. The pressure-temperature phase diagram reveals an anomalous increase of the thermal hysteresis widths with increasing pressure and the stabilization of the IP across the investigated P-T space.

Domaines: Chimie de coordination; Science des matériaux [cond-mat.mtrl-sci]

Helena Shepherd, Sylvestre Bonnet, Philippe Guionneau, Salma Bedoui, Gastón Garbarino, et al.. Pressure-induced two-step spin transition with structural symmetry breaking: X-ray diffraction, magnetic, and Raman studies. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2011, 84 (14), pp.144107. ⟨10.1103/PhysRevB.84.144107⟩. ⟨hal-00633891⟩