Network Effects On The Magnetotransport And The Complexity Of Half-metallic Oxides

In recent years, half-metallic oxides have attracted much attention for its scientific and technologic significance. In their granular systems, i.e., polycrystal, powder, and the composites with other materials, the resistance will drop rapidly and dramatically under the applied magnetic field, which is called the extrinsic magnetoresistance. On the other hand,for electronic strong correlated manganese oxide, several physical interactions——spin,charge, lattice, and/or orbital——are simultaneously active, which causes the spontaneousemergence of electronic nanometer-scale structures and the existence of many competing states. This electronic complexity could have potential consequences for applications of correlated electronic materials, such as colossal magnetoresistance (CMR). Consequently, half-metallic oxides have important fundamental meanings and extensive technological applications.In half-metallic granular systems, the extrinsic magnetoresistance effect is closely related to the spin-dependent transport processes across grain boundaries (GBs). In the early studies, the grain boundary (GB) region was usually treated as an ideal insulating barrier. The low field mangetoresistance is attributed to the electronic tunneling across the grain boundary between two ferromagnetic granules. Actually, the properties of the grain boundaries, such as the density of local spins inside it, the electronic and magnetic properties of the GB regions and etc., will play an important role in the mangetotransport processes. However, none of present models can account for all the transport processes across GBs, and the MR behaviors haven't been clearly understood.A wide variety of experimental results and theoretical investigations have convincingly demonstrated that manganese oxides are spatially inhomogeneous, due to the several simultaneously active physical degrees. It is why the early theories based on homogeneous systems are not successful. Recently, it is proposed that manganite is a kind of complex matter. However, it is not clear how to study manganite from the perspective of...