Electric field modulation of magnetic exchange in molecular helices detected by Electron Paramagnetic Resonance

The possibility to operate on magnetic materials through the application of electric rather than magnetic fields - promising faster, more compact and energy efficient circuits - continues to spur the investigation of magnetoelectric effects. Beyond symmetry requirements, large spin-orbit coupling is generally considered a necessary ingredient. On the contrary, a control of the spin-spin interaction by an electric field, not relying directly on spin-orbit coupling but rather on the overlap of the electronic clouds of interacting centers, would be quite appealing in the emerging field of quantum materials.
Here, we report the detection of a magnetoelectric effect that we attribute to an electric field modulation of the magnetic exchange interaction theoretically predicted for molecular magnetic helices. On a Manganese(II)-radical helix, thus comprising spin centers with negligible orbital contribution, the application of an electric field (E) introduces an energy contribution, which is different in case of parallel or antiparallel alignment of neighboring spins along the helix. The E field effect on the intra-chain exchange interaction J has been here experimentally observed by exploiting the sensitivity of Electron Paramagnetic Resonance (EPR) spectroscopy under electric field modulation. It is in fact well known that one-dimensional spin correlation can induce a significant g-shift even when only a weak anisotropy of dipolar origin is present. By replacing the usual B-field modulation with the E-field modulation an EPR signal is induced by the shift of the resonance as a result of the electric field effect on J. The symmetry of the observed phenomenon unambiguously confirms its magneto-chiral nature. Our observation opens interesting perspectives, which may be relevant also for the investigation of multiferroic materials.