Study On Structure, Magnetic Properties And Cation Distributions In Co_1-xFe_2-xO₄and Zn_xCo_1-xFe₂O₄

The Spinel ferrites （A）[B]2O4are of magnetic functional material, which have beeninvestigated in various applied fields, such as catalysis, filter, optical absorption, magneticmedia, medicine and new materials. Because that the microstructure and magnetic propertiesdepend on its （A） and [B] site cation distribution and spin arrangement, many efforts havebeen focused on the cation distribution and magnetic-order. So far, however, the discussionson cation distribution in these materials reported by many literatures are still in a level ofqualitative explanation.In this work, two series of ferrite samples with the composition Co₁+xFe₂-xO₄（0.0≤x≤2.0）and ZnxCo₁-xFe₂O₄（0.0≤x≤1.0） were prepared by chemical co-precipitation. The structure,magnetic properties and cation distribution are investigated:（1） Using the X-ray diffraction, we found that the two series of samples exhibited an（A）[B]2O4single phase cubic spinel structure. The crystal lattice constant, a, of samples withcomposition Co₁+xFe₂-xO₄（0.0≤x≤2.0） decreased linearly with increasing Co concent, and a ofthe samples of ZnxCo₁-xFe₂O₄（0.0≤x≤1.0） increased linearly with increasing Zn concent.（2） Specific saturation magnetization, σs, of the samples Co₁+xFe₂-xO₄（0.0≤x≤2.0） at10Kdecreases with increasing Co content x when x<1.4, with an amplitude being greatersignificantly than a value corresponding to the difference between Fe and Co ion moments;There is a local minimum at x=1.4; σsincreases from6.84with x=1.4to8.83Am2/kg withx=1.6, then decreases again to0.0Am2/kg with x=2.0. On the basis of X-ray and neutrondiffraction experiments, Roth pointed out that the Co cations form an antiferromagnetic orderat （A） sites, and a paramagnetic state at [B] sites in the cubic spinel Co3O4. Jagriti Pal examedthe Ultraviolet–Visible Spectroscopy of Co3O4, they found that the band gap energy betweenO2-and Co2+is2.28eV, and that energy between O2-and Co3+is1.57eV, suggested that thetransition probability of the electron between O2-and Co2+is obviously less than thatprobability between O2-and Co³⁺. On the basis of these experimental results, we assume thatthe angle between the magnetic moments of neighbouring metal cations in the samples Co1+xFe2-xO4（0.0≤x≤2） increases with increasing Co2+concentration over the range0≤x≤2.0,and that the antiferromagnetic phase in the （A） sublattice and the paramagnetic phase in the[B] sublattice start to appear when x=1.4, and increase with increasing x. Therefore, thedependence of average molecular moment, M, on x was fitted using the quantum-mechanicalmodel previously proposed by our group. In the fitting process, the ionicity of the materialswas taken into account. The cation distribution of the samples was calculated in the magneticmoment fitting process. The calculated Co ions content ratios occupied （A）/[B] in CoFe2O4and Co2FeO4are very close to the results that have been investigated with Mossbauerspectrum by Chandramohan and Ferreira.（3） Magnetic measurements indicated that the saturation magnetization M of the samplesZnxCo1-xFe2O4（0.0≤x≤1.0） at10K increased to a maximum when x=0.4, and then decreased.The dependence of M on x was fitted using the quantum-mechanical model previouslyproposed by our group. In the fitting process, the ionicity of the materials was taken intoaccount.The cation distribution in the samples was calculated in the magnetic moment fittingprocess. The calculated ions content ratio,0.395/0.205, occupied （A）/[B] in samples for x=0.6,which are very close to the neutron diffraction results reported by Veverka.（4） Using the cation contents at the （A） and [B] sites in the samples, calculated in theabove magnetic moment fitting process, the XRD patterns of the two series of samples werefitted with the FullProf-Suite software. The various fitting parameters are all acceptable,which indicates that the cation distributions provided by our quantum mechanical model arereasonable.