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 Mössbauer-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 $\mathrm{Co}\mathrm{}\left(A\right)-\mathrm{Fe}\mathrm{}\left(B\right)\mathrm{}$ and $\mathrm{Mn}\mathrm{}\left(A\right)-\mathrm{Fe}\mathrm{}\left(B\right)\mathrm{}$ to the $\mathrm{Fe}\mathrm{}\left(A\right)-\mathrm{Fe}\mathrm{}\left(B\right)\mathrm{}$ superexchange interactions is found to be 0.68 and 0.66, respectively. Since the Mössbauer 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.