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Electrostatic spin crossover effect in polar magnetic molecules


The magnetic configuration of a nanostructure can be altered by an external magnetic field, by spin-transfer torque or by its magnetoelastic response. Here, we explore an alternative route, namely the possibility of switching the sign of the exchange coupling between two magnetic centres by means of an electric potential. This general effect, which we name electrostatic spin crossover, occurs in insulating molecules with super-exchange magnetic interaction and inversion symmetry breaking. As an example we present the case of a family of di-cobaltocene-based molecules. The critical fields for switching, calculated from first principles, are of the order of 1 V nm−1 and can be achieved in two-terminal devices. More crucially, such critical fields can be engineered with an appropriate choice of substituents to add to the basic di-cobaltocene unit. This suggests that an easy chemical strategy for achieving the synthesis of suitable molecules is possible.

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Figure 1: Schematic illustration of the three-centre four-electron model for super-exchange.
Figure 2: Stark energy gain, ΔEGS, for the singlet and triplet states of a magnetic molecule as a function of the applied electric field, E.
Figure 3: Two of the molecules investigated in this work.
Figure 4: Total-energy calculations as a function of an external electric field.
Figure 5: Planar average of the electrostatic potential of a Au/S–[MeO–diCo]–S/Au junction at different positions.

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This work was financially supported by the SpiDME European project (6th Framework Program, NEST) and by the ERC-Starting Grant FP7-Project ‘DEDOM’ (No. 207441). S.S. and N.B. acknowledge CRANN for financial support. Computational resources were provided by NNL-SPACI, by the HEA IITAC project managed by the Trinity Centre for High Performance Computing and by ICHEC. The authors would like to thank E. Fabiano for helpful discussions and M. Margarito for technical support.

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The initial idea of the ESCE was developed by the Dublin team leader, S.S. N.B. and M.P. contributed equally to this work. M.P. carried out the DFT calculations for the exchange coupling constants, and N.B. contributed in developing the simple model and carried out the electric field drop calculations. F.D.S., M.P., S.S. and N.B. designed the molecular structures, and T.T. carried out extra DFT calculations for the exchange coupling. The project was supervised by S.S. and G.M.

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Correspondence to Stefano Sanvito.

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Baadji, N., Piacenza, M., Tugsuz, T. et al. Electrostatic spin crossover effect in polar magnetic molecules. Nature Mater 8, 813–817 (2009).

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