Triggering the Sign of Magnetic Exchange Coupling in BTBNbased compounds by means of the spin polarisation mechanism

Abstract

‘Spintronic’ devices are based on the spin-polarised electronic currents, taking profit from the intrinsic spin orientation. They are used in traditional knowledge areas such electronics, as well as in other fields of highly potential growing interest, such as quantum computing or neuromorphism. An interesting set of crystalline structures in mixed valance state for these applications are molecule-based magnets, which are usually formed by radical structures showing high spin polarisation regions. The BTBN molecule is used as a reference throughout this TFG in order to design isolated molecules intending an enhanced magnetic-exchange coupling than BTBN, considering modifications on its own basic functional units (A acceptor, C coupler or D donor), aiming at radicals to connect via the spin polarisation mechanism. The energetic study for the different spin multiplicity states, carried out using computational methods based on the Densiy Functional Theory (DFT) at a UB3LYP+6-311G(d,p) level for each proposal, is subsequently related to the value of the magnetic coupling J. Broken symmetry (BS) formalism is used in order to provide an adequate diradical description of the singlet open-shell electronic states. The performed study indicates that the called A4 radical unit derived from tetrahiafulvalene in the PA4C1D1 proposal, as a new building block candidate for the design of these organic moleculebased magnets and possible magnetoresistance due to the structural similarities with the TTF. The designed molecule PE1 using an ethylene group with an hydroxyl as C couplers is the one presenting a higher increment in the ferromagnetic exchange coupling J with respect to BTBN