Mössbauer spectra of ${\mathrm{Ni}}_{0.25}$${\mathrm{Zn}}_{0.75}$${\mathrm{Fe}}_2$${\mathrm{O}}_4$ at low temperatures ($T<\mathrm{}100\mathrm{}$ K) in the absence of an external magnetic field show a rapid decrease in the magnetic splitting and an increase in linewidths with the increase in temperature. This has been concluded to be due to the low value of the transition temperature at which the noncollinear structure changes into an antiparallel arrangement of ionic moments at $A$ and $B$ sites. The dependence of the Yafet-Kittel angle on the external magnetic field can be used to determine the exchange constants between ${\mathrm{Fe}}^{3+}$ and its neighboring ions. The splitting of the $B$-site spectrum into components with and without appreciable noncollinearity of ionic moments, however, introduces uncertainty in the determination of the exchange constants. The experimental data support a localized-canting model of spins.

• Received 17 May 1979

DOI:https://doi.org/10.1103/PhysRevB.21.1726