Structural and Mössbauer analyses of ultrafineSr1−xLaxFe12−xZnxO19 and Sr1−xLaxFe12−xCoxO19 hexagonal ferrites synthesized by chemical co-precipitation

Abstract

Ultrafine M-type hexagonal ferrites of nominal compositionSr1−xLaxFe12−xZnxO19 and Sr1−xLaxFe12−xCoxO19 with x = 0, 0.1, 0.2, 0.3 and 0.4 were produced by chemical co-precipitation. The phasemake-up of the samples was investigated by x-ray diffraction. The analyses show thatthe hexagonal M-type phase is the main phase in all the samples. Secondary(La,Sr)FeO3,ZnFe2O4 and CoFe2O4 phases are also detected, indicating that the La, Zn and Co content in the M-type phase islower than the nominal content.A complete Mössbauer analysis of the substitution effects in the M-typephase was made. The results show that the M-type phase containsLa3+ in the sameproportion as Zn2+ and La3+ in the sameproportion as Co2+, in the La–Zn and La–Co samples, respectively. The evolution withx of the hyperfine parameters of the components used to fit the contributionof the M-type phase have been interpreted consistently in relation to thesubstitution effects by means of the comparison between the spectra of theLa–Zn and La–Co substituted samples. The results show unambiguously thatLa3+ ions are locatedin the Sr2+ sites,Zn2+ ions are locatedin the 4f1 sitesand Co2+ ions arelocated in both 4f2 and 2a sites.