Electrostatic spin crossover effect in polar magnetic molecules

Abstract

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.

Singlet-Triplet Switching Induced by Electric Field in Triple Quantum Dots

“…3 that the dierence between the singlet and the triplet state increases with g E which means that the antiferromagnetic interaction increases as well. We cannot conrm the results by Baadji et al [3], where the transition from the singlet to the triplet state was induced by electric eld.…”

“…Analyzing the spectrum for the molecule with a triangular and a linear geometry we show that the singlettriplet transition can occur for the triangular symmetry only. We cannot conrm the results for the linear molecule studied in [3] for any moderated values of parameters.…”

“…3c). For the case studied by Baadji [3] the magnetic centers are represented by cobaltocene (or its derivative), which interact by the acetylene bridge. In our model we assume that the central dot 3 is diamagnetic with double electron occupation.…”

“…The singlettriplet (ST) transition was investigated in quantum dot systems by many authors, as a function of magnetic eld [1] or bias voltage [2]. Recently Baadji et al [3] found that the S T transition can be induced by electric eld in a real linear molecule. They studied, by means of the density functional theory (DFT), cobaltocene dimers, which contained two magnetic centers connected by an acetylene bridge.…”

Nonequilibrium transport response from equilibrium transport theory

“…For example, the electric field originated by the voltage bias can also shift the energy position of the molecular levels by the Stark effect, depending on the polarizability of each molecular level or on whether the molecule has itself a polar nature. 16,17 We show here a suitable modification of equilibrium transport techniques that accounts for a large set of nonequilibrium transport phenomena such as negative differential resistance (NDR) 18 or rectification effects. The performance of our method depends on the energy position, electrode coupling, and spatial localization of the molecular orbitals that are responsible for the transport properties.…”