Spin echo studies of heavily cobalt-doped ZnO:Mn2+: Electron spectral diffusion under dynamic nuclear polarization

The dynamic nuclear polarization (DNP) in a system of Mn2+ spins is studied in a weakly ferromagnetic matrix formed in heavily cobalt-doped ZnO single crystals. It is established that the thermal mixing mechanism of DNP leads to cooling of the common reservoir of electron spin-spin interactions of the Mn2+ and Co2+ spins to a single spin temperature in the rotating frame. We show the variation of the polarization amplification of the common nuclear subsystem as a function of microwave irradiation frequency.