Browsing by Author "Huang, Chun-Chao"

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Coupled microstructural and magnetic transition in Co-doped Ni nano-arrays
(2011-10-01)
Yang, Chao-Yao
;
Huang, Chun-Chao
;
Tseng, Yuan-Chieh
;
Liu, Chien-Min
;
Chen, Chih
A superparamagnetic (SM) to ferromagnetic (FM) phase transition was investigated in Co-doped (similar to 6%) electroless plated Ni arrays. The introduction of Co altered the microstructure of the Ni arrays from nanocrystalline to polycrystalline, resulting in a SM -> FM transition. This Co-induced magnetic phase transition is similar to that observed after heat treatment of undoped samples [C. M. Liu, Y. C. Tseng, C. Chen, M. C. Hsu, T. Y. Chao, and Y. T. Cheng, Nanotechnology 20, 415703 (2009); C. C. Huang, C. C. Lo, Y. C. Tseng, C. M. Liu, and C. Chen, J. Appl. Phys. 109, 113905 (2011)]. The role of Co dopant was identified electronically using x-ray magnetic spectroscopy, revealing that the transition modified the Ni host's electronic structure and enhanced its moment by effectively spin-polarizing the Ni 3d conduction band. This was distinctly different than in the heat treatment case, which underwent an electronically independent phase transition. The element-specific magnetic hysteresis of Co and Ni was also probed, which showed that the two elements were magnetically coupled. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3647753]
Instrument for x-ray absorption spectroscopy with in situ electrical control characterizations
(2013-12-01)
Huang, Chun-Chao
;
Chang, Shu-Jui
;
Yang, Chao-Yao
;
Chou, Hsiung
;
Tseng, Yuan-Chieh
We report a synchrotron-based setup capable of performing x-ray absorption spectroscopy and x-ray magnetic circular dichroism with simultaneous electrical control characterizations. The setup can enable research concerning electrical transport, element-and orbital-selective magnetization with an in situ fashion. It is a unique approach to the real-time change of spin-polarized electronic state of a material/device exhibiting magneto-electric responses. The performance of the setup was tested by probing the spin-polarized states of cobalt and oxygen of Zn1-xCoxO dilute magnetic semiconductor under applied voltages, both at low (similar to 20 K) and room temperatures, and signal variations upon the change of applied voltage were clearly detected. (C) 2013 AIP Publishing LLC.
Magnetic properties of electroless-deposited Ni and Ni-NiO core-shell nano-arrays
(2011-08-01)
Lo, Chih-Chieh
;
Huang, Chun-Chao
;
Liu, Chien-Min
;
Chen, Chih
;
Kuo, Chang-Yang
Ni and Ni-NiO core-shell nano-arrays were fabricated by means of electroless deposition, where the latter was covered by a NiO shell of similar to 10 nm by annealing the former at 350 degrees C for 30 min in an atmospheric condition. HRTEM showed that the NiO shell was developed at the expense of Ni at the array's surface. Ferromagnetic ordering of the Ni-NiO arrays was found to be suppressed compared with those of the less oxidized reference Ni arrays. This is attributed to the screening effect of the NiO shell, and weak ferromagnetism of inner Ni arrays resulted from the development of the NiO. X-ray absorption spectrum reveals that the reference Ni is partially oxidized. Also, X-ray magnetic circular dichroism suggests that the magnetic suppression of the Ni-NiO arrays is associated with a reduced spin moment. (C) 2011 Elsevier B.V. All rights reserved.
Magnetostructural phase transition in electroless-plated Ni nanoarrays
(2011-06-01)
Huang, Chun-Chao
;
Lo, Chih-Chieh
;
Tseng, Yuan-Chieh
;
Liu, Chien-Min
;
Chen, Chih
Ni nanoarrays were synthesized by electroless-plating and shaped by an anodic aluminum oxide template. The as-plated arrays exhibited superparamagnetic (SM) ordering resulting from nanocrystalline microstructure. Ferromagnetic (FM) ordering was found to be restored as the arrays' crystallinity was enhanced upon post-annealing. The microstructure (crystallinity) and the FM ordering are strongly coupled, revealing a magneto-structural correlation for the arrays. The magnetostructural properties of the arrays can be controlled by post-annealing, where the magnetization is proportional to the annealing temperature. The electroless-plated arrays synthesized in this work display magnetic anisotropy not found in electroplated ones. This is likely attributed to the nature of the clusterlike microstructure, whose cluster-boundaries may confine the FM rotation within the cluster. The spin-polarization was probed by x-ray magnetic circular dichroism while the arrays underwent the SM -> FM phase transition. The sum-rules results reveal that the total magnetization of the arrays is dominated by spin moment (m(spin)). The change in m(spin) is responsible for the SM -> FM phase transition upon annealing, as well as for the loss of magnetization upon temperature increase that we observed macroscopically. VC 2011 American Institute of Physics. [doi:10.1063/1.3594692]
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
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材料科學與工程學系
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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.