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UBC Theses and Dissertations

Giant magnetoresistance and magnetic properties of ferromagnetic hybrid nanostructures Rizal, Conrad

Abstract

Significant advances in the growth, measurement, and characterization methods in the field of nanoengineering have made Co-based magnetic hybrid (ferromagnetic and non-magnetic) nanostructures increasingly important for the development of giant magnetoresistance (GMR) sensors and high magnetic-moment biocompatible nanoparticles for use in the future magnetic technology. This thesis presents the growth, measurement, and characterization of magnetic hybrid nanostructures (multilayers, alloys, and nanoparticles) that exhibit interesting magnetoresistance (MR) and magnetic properties, which are significant in the development of state-of-the-art magnetic technology for use in the electronics and biomedical sectors. Firstly, Co/Au multilayers have been grown on glass substrates using e-beam evaporation, and then Co/Ag and Co/Cu multilayers have been grown on polyimide substrates using pulsed-current deposition. All of these multilayers exhibited the GMR effect at room temperature. The maximum MR for Co/Au, Co/Ag, and Co/Cu multilayers was 2.1 %, 9.1 %, and 4.1 %, respectively. The e-beam evaporated multilayers exhibited strong magnetic anisotropy when the films were deposited at the angle of 45 degrees. The electrodeposited multilayers exhibited strong magnetic anisotropy when strain was introduced externally. In both the cases, the GMR is strongly influenced by the ferromagnetic and nonmagnetic layer thicknesses and interfacial states between layers. Secondly, novel nanocomposites Co nanoparticles embedded in Au matrix have been developed using pulsed-current deposition on polyimide substrates. They exhibited interesting MR, grain size, and saturation magnetization characteristics. The maximum room temperature GMR found was 4.6 %. X-ray diffraction, magnetization, and low temperature measurements suggest that a smaller grain size formed during higher current density correlates with the larger MR values for these nanocomposites. Thirdly, high-magnetic-moment biocompatible FeCo nanostructures have been developed using pulsed-current deposition. The nanostructures exhibited saturation magnetization of up to 240 emu/g, which is much larger than the saturation magnetization of either Co or Fe. The less expensive and highly sensitive GMR sensors if coated with specific probes, and if the target biomolecules are labelled with high-moment biocompatible nanoparticles presented in this thesis, the GMR sensors have potential for use in improving the early detection and treatment of chronic diseases (e.g., prostate and lung cancer) using biomagnetic technology.

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