Ground state of the magnetic molecule V6 determined by broadband electron spin resonance at low frequency

We utilize a nonconventional (i.e., without resonance cavity) broadband electron spin resonance (ESR) spectrometer operating continuously in the frequency range 0.3-9 GHz to investigate the ground state of the magnetic molecule V6 at low temperature. There exist two different varieties of V6 molecules with small differences in the organic part and in the crystal packing. We find differences in the width and hyperfine structure of the ESR line in the two compounds. However, the central frequency of the broad ESR line measured vs H down to 0.3 GHz shows a linear behavior in both compounds indicating a g value close to 2 and a zero field gap no larger than 30 × 10^-3 K. The result is in contrast with a level scheme for the ground state previously reported for one of the two varieties of V6. We propose an alternative scenario for the structure of the magnetic ground state.