Effect of selenium vacancies on ferromagnetic resonance in CdCr2Se4 crystals doped with silver

The anisotropy and relaxation have been investigated in the CdCr2Se4 crystals doped with silver and subjected to various heat treatment. It is shown, that the CdCr2Se4: Ag crystal annealing in a vacuum results in the change of the sign of the anisotropy first constant. This change is related to the Cr4+ → Cr3+ → Cr2+ transitions, taking place as selenium vacancies arise. The subsequent annealing in selenium atmosphere results in the reverse change of the anisotropy sign which is related to the Cr2+ → Cr3+ → Cr4+ transitions taking place as the selenium vacancies are filled up. On the basis of obtained data assumptions are made about possible mechanisms of conductivity in the investigated crystals