The magnetic and crystalline properties of a plasma-sprayed coating of the microwave absorbing zinc-nickel ferrite, (Zn0.41Ni0.59)Fe2O4 have been studied at 300 K using the Mossbauer effect and x-ray diffraction (XRD). Both techniques indicate that the plasma-sprayed material separated into two phases. The first is a nickel-rich phase with magnetic fields of 47.5 and 44.5 T at the tetrahedral and octahedral sites, respectively. The second is a zinc-rich phase, zinc meta-ferrite, having a small magnetic field of 4.2 T. The quadrupole splitting of this second phase is DELTA-E = 0.34 mm s-1, which is the same as in pure nonmagnetic zinc ferrite. XRD analysis shows that the zinc-rich phase remains cubic with a0 = 8.389 angstrom and the zinc meta-ferrite phase is tetragonal with the same lattice parameters as the cubic phase except for one elongated axis given by c0 = 8.488 angstrom. This is much larger than the spacing for any of the series of zinc-nickel ferrites. The isomer shift of the zinc meta-ferrite is 0.710 mm s-1, which indicates that a large fraction of Fe3+ was reduced during the spraying process. Annealing the sprayed coating at temperatures less than 400-degrees-C converted the zinc meta-ferrite into a magnetic phase that now exhibits magnetic fields close to those in the nickel-rich phase. However, the large isomer shift remains, indicating that the ferrous iron is still present. XRD shows that the phase is now cubic. Annealing up to 650-degrees-C gradually oxidized all of the Fe2+ in the material and restored the magnetic and crystalline properties of the plasma-sprayed coating to very close to those of the unsprayed ferrite.
