Study Of Octahedron Structure And Properties On Perovskite Like Oxides

Perovskite like transition metal oxides have attracted considerable scientific and technological interest in rescent years. The ground state derived from the competition among lattice, spin, charge, and orbital degrees of freedom, the property can be affected by the applied electromagnetic field, pressure and temperature. Octahedron BO6is the origin of those intriguing in transition metal oxides, a delicate balance in octahedron BO6between many competing ground states creates extraordinary properties. The distortion of the octahedral unit size, shape and connectivity is believed plays a crucial role on the properties. The relationship between structure distortion and properties has attracted a great deal of attention, chemical doping is very powerful tool to induce structure distortion.In the present, we study the octahedron structure and property on several transition metal oxides. In Mn doped Sr2RuO4, we investigate the strcuture distortion near MnO6/RuO6octahedron and the enhanced ferromagnetic spin fluctuation effect. In Fe doped LaMnO3, the tilting and rotation effect between octahedrons are found and believed playing roles on the magnetic properties. The octahedral structure evolution with temperature and spin structure of quasi-two-dimensional manganese oxide Sr7Mn4O15is studied. A series of important results have been obtained from this study.1) In Sr2Ru1-xMnx04(0≤X≤0.4), no tilting and rotation of the octahedron are detected, while very clear structre distortion near MnO6/RuOe octahedron is found. Octahedral structure evolution is consistence with the change of chemical valence. Mn3+ions are dominant in the slightly Mn substitution region and Mn4+ions are dominant in the high Mn substitution region in Sr2Ru1-xMnxO4, respectively. With increasing the Mn content in Sr2RuO4, the FM property may ascribes to the enhanced FM spin fluctuation with the increasing3d electrons occupying at dxy orbital. On the contrary, spin-glass nature at low temperature is detected which originates from the competition between FM and AFM interaction. The present result will add the important information on the structure evolution which results in the enhanced FM spin fluctuation. In addition, it is also helpful for understanding the spin fluctuation mediated spin-triplet superconductivity of Sr2Ru04.2) In LaMn1-xFexO3(x=0-0.6), the tilting and rotation effect is found and may related with structure phase transition. The X-ray absorption spectra (XAS) at Mn K-edge and Fe K-edge in LaMn1_xFex03show that the chemical valence of Mn4+decreases with Fe substitution, while the iron remains the chemical valence of Fe3+. Structural distortions, such as the rotating and tilting for oxygen octahedron in the unit cell vary with iron content. A phase transition occurs at the Fe content of0.2-0.3. The evolution of rotation and tilting angle of FeO6/MnO6octahedral may be the vital factors on the structure and magnetism. We believe that the spin configuration of Fe3+may vary from the intermediate spin t2g4eg1(S=3/2) to the higher spin t2g3eg2(S=5/2) near the phase transition.3) The temperature dependent of octahedron structure and magnetic structures of Sr7Mn4O15are investigated. No rotation and tilting in corner-sharing of MnO6are detected, the connection of facing-sharing MnO6show very strong temperature dependence. ESR result shows that the g factor is around2, which is the value for free electron and attributed to the paramagnetic signal from spin clusters. A correlation is found between Mn-Mn distance, Mn-O-Mn bond length and the ESR parameters (△Hpp, Ho and Iesr) at100K. The theoretical analysis suggests the AFM state with anti-parallel spin configuration between neighboring Mn ions to be a favorable ground state for Sr7Mn4O15, which is consistent with our observation of the contraction of Mn-Mn distance between corner-sharing of Mn2O9octahedron near the AFM transition temperature.