Browsing by Author "Hsu, Hao-Chun"

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Competing magnetic interactions and interfacial frozen-spins in Ni-NiO core-shell nano-rods
(2012-03-15)
Hsu, Hao-Chun
;
Lo, Chih-Chieh
;
Tseng, Yuan-Chieh
;
材料科學與工程學系
;
Department of Materials Science and Engineering
This paper investigates the subtle interfacial magnetism of highly-aligned, free-standing Ni-NiO core-shell rods on a Si substrate, fabricated by electroless-plating and an anodic aluminum oxide template. Transmission electron microscopy found that the NiO shell was uniformly present along the entire rod. Vertical magnetization shift, arising from opposite field cooling conditions, suggests frozen spins (FS) at the Ni-NiO interface. The FS were related to the pinning effects of the NiO on the Ni. The pinning strength depended on the NiO thickness, displaying a tunable fashion from 6 to 10 nano-meters with thermal annealing. The FS mediated the antiferromagnetic (AFM)-ferromagnetic (FM) interfacial coupling, leading to the temperature-dependent properties of the rods. FS were evident below 100 K, at which the NiO-AFM dominated the properties with a suppressed coercive field and non-saturated magnetization. At 100 K, however, the Ni-FM was superior to the NiO-AFM with a restored FM phase. Meanwhile, the interfacial magnetic frustration occurred due to the disappearance of FS. These two factors resulted in the coercivity enhancement at 100 K. The uniqueness of the structure opens opportunities to tailoring the properties of the rods by manipulating the core-shell inter-dependency, as well as inspiring further researches concerning its applications in spintronics. (C) 2012 American Institute of Physics. [ http://dx.doi.org/10.1063/1.3699039]
Structural morphology and magnetism of electroless-plated NiP films on a surface-modified Si substrate
(2011-11-30)
Huang, Chun-Chao
;
Hsu, Hao-Chun
;
Tseng, Yuan-Chieh
;
材料科學與工程學系
;
Department of Materials Science and Engineering
NiP thin films were deposited on an H(3)PO(4)-etched Si substrate by means of electroless-plating. By varying the plating time, we were able to deposit NiP films with various thicknesses. Thickness effects upon the structural morphology and magnetic properties of the NiP films were investigated, and they can be comprehended with a model of the deposition mechanism. The results demonstrate that the etched Si surface contained groove-like microstructure which shaped the columnar structure inside the NiP films and favored the film deposition; this was hard to achieve with a smooth-surfaced Si substrate. The well-developed columnar structure resulted in a perpendicular anisotropy due to its vertical nature, which can become superior to the film's longitudinal anisotropy if the applied field is sufficient. (C) 2011 Elsevier B.V. All rights reserved.