The present work reports results of the 57Fe Mössbauer measurements on AgFeO2 powder sample recorded at various temperatures including the points of both magnetic phase transitions. The 57Fe Mössbauer spectra of AgFeO2 measured in the paramagnetic range (T > TN1) consist of one quadrupole doublet with rather high quadrupole splitting of Δ300K = 0.66 ± 0.01 mm/s for Fe3+ ions. In order to predict the sign of electric field gradient (EFG) at 57Fe nuclei, we calculated the lattice contribution to the electric field gradient (EFG) at 57Fe nuclei, which emphasized the importance of the dipolar contributions, with resultant oxygen polarizabilities in the range of αO = 0.83 Å3, in agreement with the results obtained previously for other delafossite-like oxides. In the temperature range of TN2 < T < TN1, Mössbauer spectra gave clear evidence for the existence of a distribution of the hyperfine magnetic fields Hhf at 57Fe nuclei. We present the results of a model fitting of the spectra based on an assumption of the cycloid magnetic structure of AgFeO2 at T < TN2. The obtained data were analysed in comparison with published data on Mössbauer studies of oxide multiferroics.
Mössbauer spectroscopy Multiferroics Frustrated magnetic interactions Iron oxides Non-collinear spin configurations
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