Second-harmonic signal in electric-field-modulated EPR spectra of Fe3 spin triangles

Abstract

We present electric-field-modulated electron paramagnetic resonance (EFM-EPR) measurements on centrosymmetric single crystals of the molecular spin triangle $[\mathrm{F}{\mathrm{e}}_3\mathrm{O}({\mathrm{O}}_2\mathrm{CPh}){}_6(\mathrm{py}){}_3]\mathrm{ClO}{}_4\cdot \mathrm{py}$ ($\mathbf{F}{\mathbf{e}}_3$). We provide the first observation of second harmonic EFM-EPR signal in polynuclear magnetic molecules. This signal is simulated and explained in terms of an electric-field induced modulation of the isotropic exchange in the molecule, and of their symmetry lowering resulting from a Jahn-Teller effect. Additionally, an unexpected first harmonic EFM-EPR signal is observed. Various plausible symmetry-breaking mechanisms are discussed in an attempt to explain this feature, whose observation is unexpected in a nominally centrosymmetric crystal.