Tansport Properties Of Metal-Insulater Granular Films

Excellent properties such as tunneling magnetoresistance (TMR), giant Hall effect (GHE), huge coercivity have made metal-insulator granular films promising candidates for the application of magnetic sensors, high density magnetic recording materials, read-out magnetic head and magnetic random access memory. Researching of new properties in these nano-structures, uncovering the mechanism of GHE, exploring the probability of GHE for practical usage, and fabrication of films with high MR at room temperature has becomes one focus in the field of condensed matter physics. This is also the aim and major work in this thesis. Different types of metal-insulator films were prepared by using magnetron sputtering, including Cu-SiO2, Zn-SiO2, NiFe-SiO2, Fe-Ge and Fe3O4-SiO2 systems. Properties such as structure, composition, resistivity, magneto-resistivity, Hall effect and magnetic properties of systems mentioned above have been carefully studied. For the first time, we find GHE in non-magnetic metal-insulator granular system, i.e. Cu-SiO2 mixture. The theory base on local quantum interference effect was proposed and has been successfully applied in Cu-SiO2 system. Through the research of Hall effect in Cu-SiO2 annealing samples and Zn-SiO2 granular system, this model has been testified. The important effect of percolating structure to GHE has been found for the first time in the comparing study on both ordinary and extraordinary Hall effect of NiFe-SiO2 system. This provides a relatively new method for understanding the mechanism in GHE. Giant enhancement of Hall resistance was firstly observed in Fe-Ge granular film and its Hall sensitivity is above one time larger that of Hall sensors which based on Si used today. This provides it a promising application for GHE. Fe3O4 films with the largest MR reported till now have been prepared at room temperature. For the fist time, anti-ferromagnetic coupling effect was found in polycrystalline Fe3O4 films. Effect of SiO2 on transport properties of Fe3O4 films was also studied. Fe3O4 film which fulfills the requirement of TMR sensors still has high MR ratio of above -5.4%, and this makes it possible for the Fe3O4 used as TMR elements.