Synthesis and Characterization of Nanostructures

Abstract

This thesis is mainly focused on synthesis and characterization of (magnetic) nanostructures in the form of multilayers and magnetic oxides thin films for spintronics applications. Exchange bias phenomenon which has a critical role in ferromagnetic/antiferromagnetic multilayer system was studied experimentally with a theoretical understanding of very recent model of exchange bias namely York Model. Standard IrMn and CoFe multilayer system (Si/Cu/IrMn/CoFe/Ta) was fabricated using High Target Utilization Sputtering (HiTUS) to study various aspects of exchange bias. Effect of Mn doping showed a decrease in the blocking temperature. Chemical reaction of Mn at the interface and diffusion of Cu from the under layer in IrMn layer were considered to be cause of this decrease. Training effect in exchange coupled IrMn and CoFe multilayer thin films was investigated for varying grain size that was controlled during the fabrication process through bias voltage. It was observed that smallest grains gave rise to a larger training effect as larger anti-ferromagnetic grain volumes give rise to thermally stable bias fields and consequently smaller training effects. The result is found reproducible and in agreement with the literature. The effects of nucleation were also studied. It was determined that nucleation arises from both sample shape effects and the process used to cut the sample. The obtained results showed that sample edge roughness leads to a distribution of nucleation fields and hence changes the shape of the hysteresis loop. It was concluded that the best way to cut samples of nucleation controlled materials is by cracking for the application in spintronics devices. Second part of the study was about Ni and Co doped TiO 2 diluted magnetic semiconductors thin films grown by Aerosol Assisted Chemical Vapor Deposition (AACVD). AACVD method was adopted for synthesizing these films due to certain advantages over other chemical routes. Further, synthesis routes may vary various properties and there are only a handful reports in the literature in which AACVD method ixwas employed to synthesize diluted magnetic oxides. Ni and Co doped TiO2 films were prepared at 450 C and 650 C respectively with Argon as a carries gas. XRD, FESEM and RBS were carried out to see phase, morphology, and stoichiometry and film thickness. Magnetic properties of the films were investigated using SQUID. Ni and Co doping resulted in ferromagnetism in TiO 2 at room temperature attributed to the formation of Bound Magnetic Polaron (BMP).