Mössbauer Study of Several Ferrimagnetic Spinels

The ferrimagnetic spinels ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$, Ni${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, Co${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, Mn${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, and Mg${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ have been prepared and studied with the M\"ossbauer-effect technique over a wide temperature range both with and without large applied magnetic fields. The cation distributions have been determined and compared with magnetization measurements. For Co${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ and Mg${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, this distribution depends on the heat treatment; two extremes---quenched and slowly cooled samples---have been investigated. The hyperfine magnetic fields at ${\mathrm{Fe}}^{57}$ nuclei in $A$ and $B$ sites have been obtained as a function of temperature. A number of hyperfine fields are identified with the $B$ sites of Co${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, Mn${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, and Mg${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ and attributed to the kind and distributions of cations in the nearest-neighbor $A$ sites. From the data, the ratio of the $\mathrm{Co}(A)\ensuremath{-}\mathrm{Fe}(B)$ and $\mathrm{Mn}(A)\ensuremath{-}\mathrm{Fe}(B)$ to the $\mathrm{Fe}(A)\ensuremath{-}\mathrm{Fe}(B)$ superexchange interactions is found to be 0.68 and 0.66, respectively. Since the M\"ossbauer spectra provides no evidence for ${\mathrm{Fe}}^{2+}$ ions in Mn${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, a canted spin arrangement for the Mn ions in $A$ and $B$ sites is proposed to account for the small observed magnetization.