Spin decoherence in an iron-based magnetic cluster

Continuous wave (cw) and pulsed high frequency electron paramagnetic resonance (HF-EPR) measurements were performed on an Fe-based magnetic cluster: Fe7O4(O2CPh)11(dmem)2, abbreviated Fe7. The cw EPR results show that two different molecular species exist in the crystal, with slightly different zero-field-splitting parameters. The spin decoherence time, T2, was measured at high magnetic fields and low temperatures, which makes it possible to obtain high spin polarization and to significantly reduce decoherence due to electron spin flip-flop processes. Theoretical fitting of T2 versus temperature shows that, for crystalline samples of this molecule, spin flip-flop fluctuations represent the main source of spin decoherence at low temperatures, as reported also for the Fe8 single-molecule magnet [Phys. Rev. Lett. 102 (2009) 087603]. Moreover, it is found that T2 is position dependent within the EPR line, a model for which is given. We also note that this is the third example of an Fe-based cluster that exhibits a measurable decoherence time, and only the second involving a crystal.

Graphical abstractContinuous wave (cw) and pulsed high frequency electron paramagnetic resonance (HF-EPR) measurements at 240 GHz were performed on an Fe7 magnetic cluster. The temperature dependence of the decoherence time T2 indicates that it is dominated by electron spin flip-flop processes. A dependence of T2 as a function of the position in the resonance line is observed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pulsed high frequency electron paramagnetic resonance on an Fe7 molecular complex. ► Temperature dependence of spin–spin relaxation time as a function of temperature. ► Quenching of spin bath decoherence at low temperatures and high magnetic fields. ► Dependence of decoherence time as a function of the position in the resonance line.