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Propriétés électroniques et spintroniques de matériaux moléculaires bistables à transition de spin et leurs applications.


Objective, Strategies

Molecular materials have been in the research spotlight since the miniaturization of silicon based devices and conventional magnetic storage devices are approaching certain technological and physical limits . In this context, the field of molecular electronics and molecular spintronics can bring genuine solutions with the synthesis and integration of compounds, which can be used as molecular switches. Within this field of research, exciting opportunities appear to generate unique electronic phenomena thanks to the tunability of molecular electronic levels at molecule/electrode interfaces. Indeed, molecular materials can be used to functionalize interfaces in organic electronic devices, leading to new electronic functionalities.

The present project focuses on the integration on electrode surfaces of a promising family of molecular switches: spin-crossover (SCO) molecules. These compounds present a special technological interest for their room-temperature bistability, as well for the coupling of electronic, magnetic and structural degrees of freedom. The use of electrical stimuli to control (read/write/erase) the spin state of the system would provide a great advantage of easier size reduction and better compatibility with current technology, while the molecular nature of these materials offers versatility and unprecedented functions. Yet, concepts for exploiting the SCO phenomenon in electronic devices are currently at a rather rudimentary stage of their development. The central aim of our work therefore is a comprehensive investigation into the possibility of exploiting SCO molecules in electronic/spintronic devices. To this aim, novel molecular (or molecule-based) SCO complexes are synthesized and integrated into elementary two- and three-terminal microelectronic devices. Since SCO leads to a sizeable variation of different physical properties (HOMO-LUMO gap, dielectric permittivity, magnetic moment, etc.), a potentially huge impact of the spin-state switching on the device properties (resistance, capacitance and magnetoresistance) can be predicted.

Yet, one has to design SCO junctions where the molecular switching phenomenon is effectively harnessed at the device level. Indeed, at present, it remains largely unknown how the SCO properties of molecules are affected by the electrode material, but this has obviously dramatic implications for their application. For this reason, it will be particularly important to achieve an in-depth experimental and theoretical analysis of the spin-state dependence of the structural, energetic and electronic properties of the complexes adsorbed on metallic electrodes.

This project is conducted in collaboration with Dr. Isabelle Séguy (LAAS-CNRS, Toulouse, France) and Dr. Aurelian Rotaru (University of Suceava, Romania).


Figure : (a) Scheme and SEM image of the cross-section of a ITO/[Fe(HB(1,2,4-triazol-1-yl)3)2]/Al junction.
(b) I – V curves of the junction acquired in the low-spin (low resistance) and high-spin (high resistance) states.

Multilayer vertical junctions

C. Lefter, S. Rat, J.S. Costa, M.D. Manrique-Juárez, C.M. Quintero, L. Salmon, I. Séguy, T. Leichle, L. Nicu, P. Demont, A. Rotaru, G. Molnár, A. Bousseksou,
Current Switching Coupled to Molecular Spin-States in Large-Area Junctions,
Adv. Mater. 28 (2016) 7508–7514.
V. Shalabaeva, K. Ridier, S. Rat, M.D. Manrique-Juarez, L. Salmon, I. Séguy, A. Rotaru, G. Molnár, A. Bousseksou,
Room temperature current modulation in large area electronic junctions of spin crossover thin films,
Appl. Phys. Lett. 112 (2018) 013301.

Of particular relevance to this project is the successful fabrication of crossbar junctions with thin films of the [Fe(H2B(pz)2)2(phen)] SCO complex sandwiched between Al and ITO electrodes. Later, this work was extended to junctions of [Fe(HB(tz)3)2] displaying SCO above room temperature.

These ground-breaking devices allowed us to trigger and probe the spin-state switching in the SCO layer by optical means, while simultaneously detecting the associated electrical resistance changes in the junctions. Notably, these junctions provided experimental evidence that the spin-state switching leads to a reversible change of the device resistance, with ON/OFF current ratios greater than 100. This effect could be correlated with the intrinsic change of the “bulk” electrical conductivity of the SCO thin layer upon spin conversion.



Laboratoire de chimie de coordination du CNRS

205 route de Narbonne, BP 44099
31077 Toulouse cedex 4