Magnetic moment directions and distributions of cations in Cr (Co) substituted spinel ferrites Ni0.7Fe2.3O4.

Powder samples of the spinel ferrites M_xNi_0.7-xFe_2.3O₄ (M = Cr, Co and 0.0 ≤ x ≤ 0.3) and Cr_xNi_0.7Fe_2.3-xO₄ (0.0 ≤ x ≤ 0.3) were synthesized using the chemical co-precipitation method. The XRD spectra confirmed that the samples had a singlephase cubic spinel structure. Magnetic measurements showed that the magnetic moments (μ_exp) per formula both at 10 K and 300 K increased with Co substitution, while the values of μ_exp decreased with Cr substitution. Applying the assumption that the magnetic moments of Cr²⁺ and Cr³⁺ lie antiparallel to those of the divalent and trivalent Fe, Co, and Ni cations in the same sublattice of spinel ferrites, these interesting behaviors could be easily interpreted. The cation distributions of the three series of samples were estimated successfully by fitting the dependences of μ_exp, measured at 10 K, on the doping level x, using a quantum-mechanical potential barrier model earlier proposed by our group. The results obtained for the Cr cation distributions at the (A) and [B] sites are very close to those obtained elsewhere using neutron diffraction. [ABSTRACT FROM AUTHOR]