Coherence Enchancement by Clock Transition and Dynamical Decoupling in S=1 Molecular Nanomagnets

Cr₇M molecular nano-magnets (MNMs) are a group of heterometallic antiferromagnetic rings containing seven Cr ions and a different metal ion. Some species like Cr₇Mn and Cr₇Co are spin-1 systems in which an avoided level crossing can occur at zero field. The transition between such levels, called clock transition, is insensitive to the fluctuations of the field. We observed enhanced coherence time T₂ at the clock transition in Cr₇Mn. Dynamical decoupling techniques like CPMG pulse trains enhance the coherence further. Away from zero field, the Cr₇Mn MNM exhibits significant Electron Spin Echo Envelope Modulation (ESEEM) signal. The comparable signal size hints at a possible additional mechanisms to preserve coherence away from clock transition through the coupling to nuclear spins. And CPMG sequence allows us to demodulate the signal and measure T₂. Consistent with continuous-wave spectra, Cr₇Mn shows pulsed EPR signals across a wide range of fields and frequencies, indicating a relatively large inhomogeneity in anisotropy of the system.