Study On The Multiphase Physical Mechanism Of Mn-based Compounds

Spinel oxides contain many interesting physical properties owing to their special structure and cation distribution,which can be impacted by the preparation method and the doped elements.In this paper,Mn-based spinel oxide was used as the research object.Co₂MnO₄ and its transition metal doped spinel were synthesized by sol-gel method.Their crystalline phases,structure,magnetic properties and dielectric properties were investigated by XRD,FT-IR,PPMS and impedance analyzer,respectively.The structure and magnetic mechanism were studied by the first principle caculation.Spinel solid solution Co_2-x-x Mn_1+xO₄ were synthesized using metal nitrates and citric acid as the starting materials.The XRD and PPMS results showed that Co_2-xMn_1+xO₄ series are single-phase cubic spinel structure at x<0.6,the lattice parameter and the saturation magnetization increase with increasing Mn content.It also revealed that Co_2-x-x Mn_1+xO₄series transform to tetragonal structure gradually at x?0.6,which leaded to the decline of magnetic properties and difficulty of reaching saturation.The magnetic measurement showed that Co_2-xMn_1+x+x O₄ was ferromagnetism,Curie temperature Tc=182 K,the saturation magnetization was 13.23 Am²/kg at 5 K.The dielectric constant indicated that Co₂MnO₄ had a dielectric anomaly and the abnormal temperature was impacted by the frequency.The transition metal?Fe/Cr/Cu/Zn?was used to substitute Co.The XRD results showed that the samples were single-phase cubic spinel structure when Fe doping content at 0.25?x?1.75 and Cr/Cu/Zn doping content at 0?x?0.3.The PPMS results showed that magnetic was found to be increasing with Fe/Cr content increasing.When Cu/Zn doped,the magnetic properties were very complexed.The changeses of lattice constant were consistent with the changes of saturation magnetization,which can declare that the lattice constant is not only determined by the atomic radius but also infulences by the internal interaction.The first principle was ued to study on the atom occputation and magnetic mechanism about Co₂MnO₄ and its doped samples.We had established the unit cell,the simulation results coincided well with he experimental data.The energy caculation results showed that Cr,Mn and Fe tend to occupy the oxygen octahedral position,Cu and Zn tend to occupy the oxygen tetrahedral position.There was a part of atomic disoder in actual materials.The magnetic caculation also showed that Co₂MnO₄ is ferromagnetism:the magnetic moments of Co and Mn at oxygen octahedral position were arranged in parallel,and the magnetic moment of Co at oxygen tetrahedral position were opposite.When incorporated Mn/Fe,the magnetic increased,because the atomic moment of Mn/Fe was larger than the original Co,and increased the magnetic interaction between the dopant atoms and the original Mn and Co.When incorporated Cr,the magnetic also increased,because incorporation of Cr reduced the antiferromagnetic,thereby enhancing the ferromagnetism.