The Study Of Magnetotransport In Half-metallic Granular Systems

In recent years, the half-metallic oxides are paid attention to as a result of the important theory value and the widespread application prospect. In the half metal oxide compound polycrystal, cold-press in powder and other material, the resistance will drop rapidly and dramatically under the applied magnetic field, this with intrinsic properties of material is inseparable, but its crystal boundary played similarly the very important role, the extrinsic magnetorresistance effect is closely related to the transport process grain boundaries. The difference properties of the grain boundaries, has caused the complex changeable magnetorresistance behavior. However, none of theoretical model which already established at present can make the comprehensive description to the intergranular transport process, therefore the important question in the determination the occupied the dominant position transportation mechanisms of grain boundaries and to the macroscopic transportation behavior contribution was one of the current correlation research.This purpose of the work is to study the magnetotransport of half-metallic oxides. The main results of our study are listed as follows:1. The effect of remanence on magnetorresistance in half-metallic oxides granular systems. Take the cold-press chromium dioxide powder as the object of study, considered the chromium dioxide powder granular surface has trioxide two chromium, along with the annealing time increase, trioxide two chromium level thickness also correspondingly increases, the neighboring intergranular insulating is more and more good, we think a neighboring two granular constitution nanometer criterion "the spinning valve"; the electronic transportation form one to other granular is elastic direct tunneling; because the insulating layer existence localized states (density of local spins), electron besides direct tunneling, but also may hopping along the density chain of local spins in insulating layer. We use the double channel model, one is the spin-dependent elastic direct tunneling channel, another is the spin-independent channel which is higher order inelastic hopping through two or more localized states. First proposed t The effect of remanence on magnetorresistance, the remanence existence causes value of the magnetorresistance to reduce. Explained the cold-press chromium dioxide powder system experimental phenomenon.2. The study of network effects in half-metallic oxides granular systems. Take the cold-press chromium dioxide powder, the powder and the polytropism of double perovskite structureSr₂FeMoO₆ as the objects of study, considered the powder granular surface existence insulating layer,the neighboring intergranular electronic transportation has two kind of leading mechanisms (spin-dependent elastic direct tunneling and spin-independent higher order inelastic hopping), the use random resistance network model, puts in randomly two resistances according to certain component in the network, we thought the identical material the different powder experiment phenomenon difference belongs to two kind of leading mechanism competition the result, explained the corresponding experimental phenomenon well. The resistance network model is more suitable for to describe the granular system transportation properties than parallel and series connected model obviously.