博士 / 國立東華大學 / 物理學系 / 103 / The possibility of size dependency of the optical and magnetic properties of nanostructured 3d transition metal oxides has opened up the path for extensive research activities in recent years. In this thesis, we report a unique synthesis technique and a comprehensive step wise characterization process to describe the effect of finite size and nickel vacancies on the optical and magnetic properties of NiO nanoparticles with size varying from 16.6(7) to 54(6) nm. The XRD study reveals short-range crystallinity. The finite size effect with nickel vacancies resulted in the formation of uncompensated antiferromagnetic nanoparticles with frustrated and disordered spins at the surface. Due to high nickel vacancies, the superexchange mechanism relaxes and shows short-range magnon excitation in small size nanoparticles at room temperature. A critical size of
~11 nm was predicted below which, due to enhanced nickel vacancies, magnon excitation disappears. Magnetic measurement unveil the existence of ferromagnetic and antiferromagnetic component in small size NiO nanoparticles. Relaxation dynamics
reveal that system of small size particles is poly-dispersed/densely packed (16.6(7) nm, n = 0.93) resulting in interparticle interactions because of ferromagnetic component. A
spontaneous exchange bias (SEB) phenomenon was observed in small sized interacting nanoparticles, which disappear in large sized particles due to reduced FM component. The observed SEB effect is attributed to the intercoupling of spins at the interface of
short-range ordered clusters of spins which behave like FM to the uncompensated AFM.
| Identifer | oai:union.ndltd.org:TW/103NDHU5198005 |
| Date | January 2015 |
| Creators | Ashish Chhaganlal Gandhi, 甘地亞旭 |
| Contributors | Sheng-Yun Wu, 吳勝允 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 112 |
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