Nanocrystalline ${\mathrm{NiFe}}_2{\mathrm{O}}_4$ spinel has been synthesized with various grain sizes by high-energy ball milling. From the high-field magnetization studies and extended x-ray-absorption fine-structure, and Mössbauer measurements in an external magnetic field of 5 T applied parallel to the direction of gamma rays, we could observe that ${\mathrm{Ni}}^{2+}$ ions occupy tetrahedral sites on grain-size reduction due to milling. The ${\mathrm{Fe}}^{3+}$ spins have a canted structure and the canting angle increases with grain-size reduction. It is possible that the core ${\mathrm{Fe}}^{3+}$ spins are also canted because of the magnetocrystalline anisotropy introduced by the occupancy of the ${\mathrm{Ni}}^{2+}$ ions in the tetrahedral sites.

• Received 9 October 2000

DOI:https://doi.org/10.1103/PhysRevB.63.184108