| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 106 === A multiferroic composite film with a combination of ferrimagnetic Ni0.5Zn0.5Fe2O4 (NZFO) and multiferroic BiFeO3 (BFO) was grown on the LaNiO3 (LNO) buffered Si (001) substrate using dual-target RF magnetron co-sputtering. LNO polycrystalline films were prepared for a nanocolumnar structure and were confirmed with SEM. The effect of temperature, partial oxygen pressure (pO2), and working pressure are presented here, where at a lower working pressure, 10 and 20 mtorr, no columnar structures devoloped due to a deviated Ni/La ratio. In response to changes in temperature, the columns become finer as temperature decreased. The diameters of the columns were 59.4, 69.0 and 97.3 nm at 550, 650 and 750oC, respectively, as measured using AFM. Higher pO2 revealed fine columns, which was confirmed via SEM. Such a nanostructure is expected to minimize the “substrate clamp” problem that limits the applications of this type of composite films. BFO + NZFO composite films were deposited on columnar structures with different diameters. Exchange bias was provided to ensure there was no interfacial diffusion between the composite were BFO particles embedded in the NZFO matrix, as confirmed with TEM. The longitudinal coefficient (αE,L) and transverse coefficient (αE,T) were measured. All results showed αE,T to be larger than αE,L. BFO and LNO showed grain epitaxy cause higher αE,L that decreased with increases in thickness. This residual strain was relaxed by the columns in the in-plane direction; thus, αE,T enhanced as thickness increased. For composites deposited on LNO of the fine columns, αE,L and αE,T are 2.056 and 2.759 V·Ohm-1cm-1 under a 0 bias field at the resonance frequency of 4 kHz, as the thickness increased to 300 nm, and the αE,L and αE,T are 1.292 and 3.071 V·Ohm-1cm-1 under a 0 bias field at the resonance frequency of 4 kHz.
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