C. Y. Hsu

National Sun Yat-sen University, Kao-hsiung-shih, Kaohsiung, Taiwan

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Publications (13)31.32 Total impact

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    ABSTRACT: The magnetic and magneto-transport properties of Ni nanowire (NW) arrays, fabricated by electrodeposition in anodic-aluminum-oxide (AAO) templates, have been investigated. The AAO pores have diameters ranging from 35 to 75 nm, and the crystallinity of the Ni NW arrays could change from poly-crystalline to single-crystalline with the [111] and [110] orientations based on the electrodeposition potential. Notably, double switching magnetization loops and double-peaked magnetoresistance curves were observed in [110]-oriented NWs. The crystalline orientation of the Ni NW arrays is found to influence the corresponding magnetic and magneto-transport properties significantly. These magnetic behaviors are dominated by the competition between the magneto-crystalline and shape anisotropy.
    Nanotechnology 10/2010; 21(42):425602. DOI:10.1088/0957-4484/21/42/425602 · 3.67 Impact Factor
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    ABSTRACT: This work demonstrates, by frequency-dependent electrical measurements, significant variation associated with interfacial defects in Co/ZnO nanocomposites (NCs) for electrical and magnetic transport. Radio-frequency impedance measurements showed that heat treatment in an ultrahigh vacuum (UHV) increased interfacial defect density. Interfacial defects-assisted transport reduced the magnetoresistance (MR) ratio from 5.04% for the as-grown sample to 0.17% following heat treatment in UHV. The evolution of the onset frequency of power-law dispersion conductivity revealed that the increase in the interfacial defect density in Co/ZnO NCs upon heat treatment was consistent with the change in MR.
    Applied Physics Letters 02/2009; 94(5). DOI:10.1063/1.3077312 · 3.52 Impact Factor
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    ABSTRACT: CoFe–MgO–CoFe magnetic tunnel junctions (MTJs) were fabricated by means of ion beam sputtering of MgO as well as subsequent thin films on CoFe. We demonstrated that when a submonolayer of Mg was deposited on the CoFe layer prior to the deposition of MgO, profound improvement in the performance of the CoFe–Mg–MgO–CoFe MTJ was achieved compared to that without the Mg layer. ac impedance measurement indicated that the interfacial Mg layer resulted in fivefold increase in the magnetoresistance ratio from 0.76% for MTJs without it to 4% for that with it. Complex-capacitance (CC) spectra of MTJs showed that the contribution in the relaxation frequency by textured MgO increased. This indicated that the submonolayer Mg improved the texture of the subsequently deposited MgO. Bias-dependent complex-impedance (CI) spectra reveal that interfacial defects were also suppressed due to the submonolayer of Mg. Results obtained from x-ray reflectivity and transmission electronic microscopy were also consistent with those of CI and CC.
    Journal of Applied Physics 11/2008; 104(7-104):073909 - 073909-4. DOI:10.1063/1.2991439 · 2.19 Impact Factor
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    ABSTRACT: We demonstrate tunable magnetic order of cobalt nanoparticles in Co/ZnO nanocomposites. High-density electronic states in ZnO formed during high vacuum annealing help generate bound and free charge carriers, which in turn enable the stable magnetic ordering of Co nanoparticles in the Co/ZnO nanocomposites in a tunable manner. This is demonstrated by the following experimental observations: (i) enhanced spontaneous magnetization and coercivity, (ii) transition from semiconducting to metallic electrical-transport, and (iii) transverse magnetotransport transition from negative magnetoresistance to the anomalous Hall effect. The work explores a route to manipulate the magnetic order of magnetic nanoparticles by means of intentionally generated defects in oxides.
    Applied Physics Letters 08/2008; 93(7):072506-072506-3. DOI:10.1063/1.2959081 · 3.52 Impact Factor
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    ABSTRACT: The interlayer coupling of CoFeB-based synthetic antiferromagnets SyAFs, modulated by the ion-beam assisted deposition IBAD has been systematically investigated under different assisted deposition voltage from 0 to 140 V. We observe that proper IBAD voltage can significantly enhance the antiferromagnetically coupled saturation field from 280 to 1000 Oe and retain the amorphous structure of CoFeB layers. This approach provides a convenient method to enhance the magnetic coupling of SyAFs, which is useful for the magnetic tunnel junctions fabrication and magnetoresistive random access memory development. © 2007 American Institute of Physics.
    Journal of Applied Physics 06/2007; 101(12). DOI:10.1063/1.2748860 · 2.19 Impact Factor
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    ABSTRACT: We have systematically investigated the complex impedance (CI) and complex capacitance (CC) spectra of MgO-based magnetic tunnel junctions (MTJs) due to successive annealing. The variation of the tunnel magnetoresistance (TMR) ratio due to annealing can be related to the change of interfacial trap states and textured MgO based on the analysis of CI spectra by an equivalent circuit model. The results of CC spectra are also consistent with the analysis of CI and observed TMR ratio variation. The CI and CC techniques are also powerful to characterize the oxide-based MTJs
    IEEE Transactions on Magnetics 03/2007; DOI:10.1109/TMAG.2006.888502 · 1.21 Impact Factor
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    ABSTRACT: The field-dependent complex impedance (CI) spectroscopy is employed to clarify the origins of ac magnetoimpedance (MI) effects at room temperature near the conduction threshold of [ La <sub>0.67</sub> Sr <sub>0.33</sub> Mn O <sub>3</sub>(113)]<sub>1-x</sub>/[ La <sub>1.67</sub> Sr <sub>1.33</sub> Mn <sub>2</sub> O <sub>7</sub>(327)]<sub>x</sub> composites. The field-dependent CI spectra in 113-327 granular composites are further transformed to field-dependent magnetoconductance (MC) spectra. The frequency-dependent high-field and low-field MC spectra can be well interpreted by including the trap-state contributions in 113-327 interfaces and 327 grain boundaries, together with the leakage-region-induced spin-dependent quantum well state effect. The principle of this work could be applied to study the magnetoresistance and MI effects of magnetic granular composites.
    Applied Physics Letters 01/2007; 89(26-89):262510 - 262510-3. DOI:10.1063/1.2422880 · 3.52 Impact Factor
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    ABSTRACT: The electrical transport characterization of dual-layer perovskite, La<sub>1.4</sub>Sr<sub>1.6</sub>Mn<sub>2</sub>O<sub>7</sub> (327), has been systematically studied by the complex impedance technique. The complex resistivity spectra, under a dc bias (V<sub>dc </sub>) from 0 to 400 mV, have been analyzed by an equivalent circuit model (ECM), including a resistance (R) component and two sets of parallel R and capacitance (C) components in series. The electrical elements represent the 327 grain and 327 two different (extrinsic and intrinsic) grain boundaries (GBs) contributions, respectively. The analyzing results by the ECM demonstrate the R decreases, but C increases with rising V<sub>dc</sub> for extrinsic phase of 327 GBs. The behavior can be assigned to the trap-states dominated conduction. For intrinsic phase of 327 GBs, R is almost independent on the V<sub>dc</sub> but C decreases with rising V<sub>dc</sub>. The transport behavior can be attributed to the decrease of electric dipoles rotation by increasing V<sub>dc</sub>. It is here noted that the R element of 327 grains is almost independent on V<sub>dc</sub>. The results indicate that two phase GBs is a predominant effect on the electrical transport for 327 and exists different transport behavior on V<sub>dc</sub>
    IEEE Transactions on Magnetics 11/2006; DOI:10.1109/TMAG.2006.878875 · 1.21 Impact Factor
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    ABSTRACT: The electrical transport characterization of dual-layer perovskite, La 1 4 Sr 1 6 Mn 2 O 7 (327), has been systematically studied by the complex impedance technique. The complex resistivity spectra, under a dc bias (V dc) from 0 to 400 mV, have been analyzed by an equiv-alent circuit model (ECM), including a resistance () component and two sets of parallel and capacitance () components in series. The electrical elements represent the 327 grain and 327 two different (extrinsic and intrinsic) grain boundaries (GBs) contributions, respectively. The analyzing results by the ECM demonstrate the decreases, but increases with rising dc for extrinsic phase of 327 GBs. The behavior can be assigned to the trap-states dominated conduction. For intrinsic phase of 327 GBs, is almost independent on the dc but decreases with rising V dc . The transport behavior can be attributed to the decrease of electric dipoles rotation by increasing dc . It is here noted that the element of 327 grains is almost independent on dc . The results indicate that two phase GBs is a predominant effect on the electrical transport for 327 and exists different transport behavior on dc . Index Terms—Colossal magnetoresistance, complex impedence, equivalent circuit model.
    IEEE Transactions on Magnetics 01/2006; 42. · 1.21 Impact Factor
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    ABSTRACT: The effects of metal-insulator interfacial roughness, modulated by Ar + irradiation, on bias dependence of tunnel magnetoresistance TMR and electrical transport of CoFe– AlO x – CoFe magnetic tunnel junctions MTJs have been studied. Reduction of TMR ratio and asymmetric TMR falloff curves as a function of dc bias have been observed for Ar + -irradiated MTJs. The results are analyzed by x-ray reflectivity together with complex impedance techniques, indicating interfacial roughness which likely results in a proportional rising trap state density TSD. Increasing TSD for Ar + -irradiated MTJs increases an unpolarized current which decreases TMR ratio. The asymmetric TMR falloff curves are attributed to the different TSDs of bottom and top CoFe– AlO x interfaces in tunneling process. © 2005 American Institute of Physics.
    Journal of Applied Physics 11/2005; 98(10). DOI:10.1063/1.2132096 · 2.19 Impact Factor
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    C.Y. Hsu, J.C.A. Huang
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    ABSTRACT: The bias-dependent complex impedance spectra of ion-beam sputtered CoFe-AlO<sub>x</sub>-CoFe tunnel junctions have been systematically investigated. An equivalent circuit model, composed of a resistance component and two sets of parallel resistance (R) and capacitance (C) components in series, has been utilized to describe the individual impedance contribution from lead of cross patterns, CoFe-AlO <sub>x</sub> interfaces and bulk AlO<sub>x</sub> in CoFe-AlO<sub>x</sub>-CoFe tunnel junctions. The fitting results reveal that the RC component characterizing the CoFe-AlO<sub>x</sub> interface can be explained by a Schottky barrier with imperfectly blocking characteristic, which is attributed to the existence of traps in the depletion region. The tendency of interfacial resistance, R<sub>i</sub>, and interfacial capacitance, C<sub>i</sub>, as a function of dc bias, V<sub>dc</sub>, is expected for the space charge limited current model with exponential trap distribution, which coincides with the analyzing results of dc four-probe current-voltage curves. On the other hand, the R and C components of bulk AlO <sub>x</sub> almost remain constant when V<sub>dc</sub> increases, in contrast to the electrical behavior of CoFe-AlO<sub>x</sub> interfaces. The results suggest the metal-insulator interface, instead of bulk insulator, dominates the electrical transport process of MTJs.
    IEEE Transactions on Magnetics 11/2005; DOI:10.1109/TMAG.2005.854712 · 1.21 Impact Factor
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    J C A Huang, CY Hsu
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    ABSTRACT: The complex impedance spectra of CoFe–AlO x –CoFe tunnel junctions with under-, proper-, and overoxidized tunnel barriers have been investigated by ac impedance techniques. Two sets of parallel resistance R and capacitance C elements and a R element in series, modeling the impedance contributions of the metal-oxide interfaces and bulk insulating layers, are employed to describe the impedance spectra of under-and proper-oxidized junctions. This model, however, reveals a discrepancy for overoxidized junctions. This discrepancy can be reconciled by including a third set of parallel RC element, which suggests the appearance of overoxidized CoFeO x layer upon the bottom electrode. From further analysis of interfacial capacitance as a function of oxidation time, the bottom interfacial capacitance widely diverges from the top interfacial capacitance and can be related to the oxidation process of tunnel barrier. The analyzing results of impedance technique are also consistent with the results by complex capacitance technique. © 2005 American Institute of Physics.
    Journal of Applied Physics 09/2005; 98(6). DOI:10.1063/1.2058177 · 2.19 Impact Factor
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    J. C. A. Huang, CY Hsu
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    ABSTRACT: Proper as well as under- and over-oxided CoFe−AlOx−CoFe magnetic tunnel junctions (MTJs) have been systematically investigated in a frequency range from 102 to 108 Hz by complex capacitance spectroscopy. The dielectric relaxation behavior of the MTJs remarkably disobeys the typical Cole–Cole arc law probably due to the existence of imperfectly blocked Schottky barrier in the metal-insulator interface. The dielectric relaxation response can be successfully modeled on the basis of Debye relaxation by incorporating an interfacial dielectric contribution. In addition, complex capacitance spectroscopy demonstrates significant sensitivity to the oxidation process of metallic Al layers, i.e., almost a fingerprint of under, proper, and over oxidation. This technique provides a fast and simple method to inspect the AlOx barrier quality of MTJs.
    Applied Physics Letters 12/2004; 85(24):5947-5949. DOI:10.1063/1.1835534 · 3.52 Impact Factor

Publication Stats

59 Citations
31.32 Total Impact Points

Institutions

  • 2010
    • National Sun Yat-sen University
      • Department of Physics
      Kao-hsiung-shih, Kaohsiung, Taiwan
  • 2005–2009
    • National Cheng Kung University
      • Department of Physics
      臺南市, Taiwan, Taiwan
  • 2004–2007
    • National Chung Cheng University
      Chia-i-hsien, Taiwan, Taiwan