S. H. Liou

University of Nebraska at Lincoln, Lincoln, Nebraska, United States

Are you S. H. Liou?

Claim your profile

Publications (289)562.53 Total impact

  • Yi Wang · D. Le Roy · Jun Jiang · Xiaolu Yin · H. X. Wei · S. H. Liou · X. F. Han ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The nonlinear temperature dependence of nucleation field (Hn) of [Co/Pt]n multilayer based perpendicular magnetic tunnel junction stacks with wedged Co60Fe20B20 insertion layers is reported. When temperature decreases, the tilted spins away from perpendicular direction near Co60Fe20B20/AlOx interface play dominating role to promote the nucleation process and lower Hn value and even change the sign of Hn. By taking advantage of high temperature annealing under high perpendicular magnetic field, this nonlinear behavior and sign of Hn could be manipulated. The understanding of temperature dependent properties in such system is important for spintronics applications, such as in memory and spin oscillators.
    Journal of Applied Physics 04/2013; 113(17). DOI:10.1063/1.4801406 · 2.18 Impact Factor
  • Yi Wang · Xiaolu Yin · D. Le Roy · Jun Jiang · H. X. Wei · S. H. Liou · X. F. Han ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The [Co/Pt]n multilayer based perpendicular magnetic tunnel junction stacks with wedged Co60Fe20B20 insertions up to 2 nm, and corresponding perpendicular magnetic tunnel junctions were magnetically and electrically investigated. The focus is on the influence of CoFeB insertions in the free and reference electrodes on the overall junction magnetization reversal and magnetoresistance response. The exchange spring behavior was revealed as the Co60Fe20B20 spins canting towards the in-plane direction in the [Co/Pt]n/Co60Fe20B20 hard/soft perpendicular magnetic electrodes. The broad range thickness of wedged Co60Fe20B20 insertion enables to reveal the critical transition, in particular, from rigid coupling to exchange spring coupling. With the help of 375°C annealing under 10 kOe magnetic field, the recovery from distinct multi-domain structure to nearly single domain structure was distinctly observed in the unpatterned perpendicular magnetic tunnel junction (p-MTJ) films with CoFeB thickness tCFB ≥ 1.5 nm. Meanwhile, for the corresponding patterned perpendicular magnetic tunnel junctions with AlOx barrier, the tunnel magnetoresistance (TMR) ratio exhibited an intense enhancement over 100%. The TMR results and spin configurations were illustrated using an exchange spring model in both magnetic electrodes. The presented study shows the benefit of using exchange spring magnetic electrodes in perpendicular magnetic tunnel junction on their performance.
    Journal of Applied Physics 04/2013; 113(13). DOI:10.1063/1.4798507 · 2.18 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Anatase TiO2 is known as a promising host material for a wide-gap ferromagnetic semiconductor as it is a good solvent for numerous transition-metal elements. We report on the structural and magnetic properties of epitaxially grown anatase (Ti1−xVx)O2 layers where x covers the whole range of solubility of V atoms in anatase TiO2 and beyond the solubility limit of 21%. We measured an average magnetic moment per vanadium as high as 1 µB with a magnetic percolation threshold of less than 6% which agrees with recent theoretical predictions. Interestingly, our results show a decrease of the average V magnetic moment as x increases throughout the solubility range. Anatase (Ti1−xVx)O2 is no longer present beyond the solubility limit, where the nonmagnetic VO2 phase forms and destroys the net magnetization.
    Journal of Applied Physics 03/2012; 111(7). DOI:10.1063/1.3679434 · 2.18 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate a simple low-power, magnetic sensor system suitable for high-sensitivity magnetic-field mapping, based on solid-state magnetic tunnel junction devices with minimum detectable fields in a 100 pT range at room temperature. In this paper, we discuss a method that uses multilayer thin films to improve the performance of the soft ferromagnetic layer in magnetoresistive sensor applications, by reducing the coercivity and/or improving the reversibility. We have used it in the design of our new magnetic sensor. This sensor has a sensitivity as high as 750%/mT. The magnetic sensor only dissipates 1 mW of power while operating under an applied voltage of 1 V.
    IEEE Transactions on Magnetics 10/2011; 47(10):3740-3743. DOI:10.1109/TMAG.2011.2157997 · 1.39 Impact Factor
  • D. Le Roy · W. Yang · X. Yin · R. Y. Lai · Sy_Hwang Liou · David J Sellmyer ·
    [Show abstract] [Hide abstract]
    ABSTRACT: A scheme for molecular sensing using magnetic tracer particles and a microcantilever torsional magnetometer is investigated. The present report deals with the example of explosive 2,4,6-trinitrotoluene (TNT) detection. The sensors consist of silicon microcantilevers functionalized with TNT aptamers that are weakly bonded to magnetic particles via TNT-analog molecules. When exposed to TNT, the magnetic signal, initially maximum, is expected to undergo a steplike decrease as the TNT molecules replace the magnetic particles on the TNT receptors. We demonstrate the feasibility of this detection technique in terms of chemical reactions and our magnetometer sensitivity that reaches the range of 10<sup>-11</sup> emu at room temperature with commercial atomic force microcopy cantilevers.
    Journal of Applied Physics 05/2011; 109(7-109):07E532 - 07E532-3. DOI:10.1063/1.3564951 · 2.18 Impact Factor
  • X. L. Yin · S. H. Liou · A. O. Adeyeye · S. Jain · B. S. Han ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The magnetization reversal in patterned thin-film arrays of elliptical submicron permalloy elements has been investigated by magnetic-force microscopy and micro-magneto-optic Kerr effect. Three different spatial arrangements of chains are considered, namely chains aligned parallel to the long axis of the ellipse, chains aligned parallel to the short axis of the ellipse, and arrays with roughly equal element-to-element spacings in both directions. Comparison of the hysteresis loops in an in-plane field perpendicular to the ellipses' long axes shows that the magnetization reversibility is highest for chains along the long axis. This is due to the nearly coherent magnetization rotation in the applied magnetic field and to the formation of a head-to-tail domain arrangement. Other arrangements, such as chains of ellipses aligned parallel to short axis, yield flux-closure domains as the applied magnetic field is changed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567180]
    Journal of Applied Physics 04/2011; 109(7-7). DOI:10.1063/1.3567180 · 2.18 Impact Factor
  • Source
    S. H. Liou · Gang Xiao · C. L. Chien · K. M. Unruh ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Multilayer films consisting of alternating Fe and Cu thin films have been made by a twin-gun sputtering device with a rotating substrate platform. Both proportional modulated films and films with a fixed Cu layer have been fabricated, where the Fe layer has been varied between 10 and 150 Å. These films have been studied by x-ray diffraction, Mössbauer spectroscopy and SQUID magnetometry. Thin Fe layers with thicknesses less than 25 Å, exist only as fee α-Fe. Thicker Fe layers contain both bcc and fcc Fe. The interface between Fe and Cu appears very sharp with no evidence of Fe-Cu alloys. The α-Fe state orders magnetically below 100 K with a small magnetic moment.
  • A. R. Kortan · M. Hong · J. Kwo · P. Chang · C. P. Chen · J. P. Mannaerts · S. H. Liou ·

    MRS Online Proceeding Library 01/2011; 811. DOI:10.1557/PROC-811-E1.2
  • S.H. Liou · Y.X. Zhang · R.J. Deangelis ·

    MRS Online Proceeding Library 01/2011; 195. DOI:10.1557/PROC-195-451

  • MRS Online Proceeding Library 01/2011; 231. DOI:10.1557/PROC-231-329
  • Q. L. Xu · M. T. Liu · Y. Liu · C. N. Borca · H. Dulli · P. A. Dowben · S. H. Liou ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We have successfully grown La0.65Pb0.35MnO3 thin films by a RF magnetron sputtering method onto (100) LaAlO3 single crystal substrates. X-ray diffraction measurements are consistent with a (100) cubic orientation of the films. The fourfold symmetry showed by LEED(Low Energy Electron Diffraction) patterns indicate that the films have surface order. STM(Scanning Tunneling Microscopy) measurements indicate that the surface of the films were smooth, with approximate 5 nm roughness. XPS (X-ray Photoemission Spectroscopy) shows that the surface defect density in the films is comparatively low. The bulk magnetization of the films at 6K in 1 T magnetic field reached 77 emu/g and a Curie temperature near 354 K, close to maximum resistivity. A negative magnetoresistance of 47% was observed at 320K in 5.5 T magnetic field.
    MRS Online Proceeding Library 01/2011; 602. DOI:10.1557/PROC-602-75
  • [Show abstract] [Hide abstract]
    ABSTRACT: We compare the magnetization versus temperature, determined by magnetic circular dichroism, with bulk magnetization determined by SQUID magnetometery. The results for two different manganese perovskites, Lao0.65A0.35MnO3 systems (A=Pb, Sr), epitaxially grown on LaAlO3 substrates compared. The results suggest that the magnetic circular dichroism results may not be representative of the bulk magneti zation. Similar materials, but with a different secondary electron mean free path lengths or different surface compositions, may thus be expected to have different behavior in MCD or MXLD that depends on a photoyield for detection.
    MRS Online Proceeding Library 01/2011; 602. DOI:10.1557/PROC-602-301
  • S. H. Liou · C. H. Chen · H. S. Chen · A. R. Kortan · C. L. Chien ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The coercivity of granular Fe embedded inside an SiO2 matrix was as high as 3 kOe at 6K, and 1.1 kOe at 300K. In this study, we observed a linear temperature (T) dependence of the coercivity for the samples prepared at a high substrate temperature (773K), and a T1/2 dependence of the coercivity for the sample prepared at a low substrate temperature (473K). This indicates that the microstructures of films prepared at different substrate temperatures are not the same. This phenomenon can be explained if we assume that there are interconnections between particles for the sample prepared at a high substrate temperature. We looked for evidence of interconnections between particles with transmission electron microscopy (TEM).
    MRS Online Proceeding Library 01/2011; 132. DOI:10.1557/PROC-132-191
  • C. L. Chien · S. H. Liou · M. Natan ·

    MRS Online Proceeding Library 01/2011; 77. DOI:10.1557/PROC-77-387
  • S. H. Liou · C. L. Chien ·

    MRS Online Proceeding Library 01/2011; 80. DOI:10.1557/PROC-80-145

  • MRS Online Proceeding Library 01/2011; 274. DOI:10.1557/PROC-274-177
  • Source
    Ralph Skomski · R. Zhang · P. Kharel · Axel Enders · Sy_Hwang Liou · D. J. Sellmyer ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The mesoscopic Kondo effect in metallic nanoparticles containing a magnetic impurity is investigated by model calculations. A Maxwell–Garnett approach is used to approximately determine the resistivity of doped nanoparticles in a matrix, and the magnetic susceptibility is estimated from the confinement of the conduction electrons. Conductivity measurements of nanoparticles embedded in a matrix are difficult to realize, because metallic matrices distort the Kondo cloud, whereas insulating or semiconducting matrices yield a very weak signal. By comparison, susceptibility measurements do not suffer from these shortcomings. The Kondo effect survives in nanoparticles even if the cluster size is much smaller than the Kondo screening cloud, but the effective Curie constant becomes constant below a particle-size dependent transition temperature and the temperature dependence of the susceptibility is no longer universal.
    Journal of Applied Physics 06/2010; 107(9-107):09E126 - 09E126-3. DOI:10.1063/1.3365134 · 2.18 Impact Factor
  • Source
    R. Zhang · R. Skomski · X. Yin · S. H. Liou · D. J. Sellmyer ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Soft bilayer alloys were produced by depositing granular Fe: SiO2 onto transition-metal thin films. We have prepared series of samples using different soft-magnetic materials including permalloy (Ni80Fe20), hcp Co90Fe10, and amorphous Co60Fe20B20, all covered by a layer of superparamagnetic Fe particles in a silicon-oxide matrix. The thickness of transition-metal layer was fixed and the magnetic properties of the bilayer system were studied by varying the Fe: SiO2 layers thicknesses from 0 to 70 nm. The bilayer yields a moderate improvement of the soft-magnetic performance. The hysteresis loops show a pronounced twofold anisotropy in the film plane for permalloy and amorphous CoFeB, which is consistent with the presence of external magnetic field during processing. This indicates that the coercivity is controlled by the pinning of 180 degrees domain walls and that the effect of the Fe particles on the hysteresis is mediated by the interaction with the domain-wall stray fields. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3360768]
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a design of a low power, compact, magnetoresistive sensor. The key features of the design are (1) decreasing the noise by the use of a 64 element magnetic tunnel junction (MTJ) bridge, (2) reducing the magnetic noise by annealing of the MTJ sensors in high magnetic field and a hydrogen environment, and (3) increasing the signal by the use of external low-noise magnetic flux concentrators. The field noise of our prototype magnetic sensor is approximately 4.5 pT/Hz<sup>1/2</sup> at 1 kHz, and 222 pT/Hz<sup>1/2</sup> at 1 Hz at room temperature. The magnetic sensor dissipates about 2 mW of power while operating at an applied voltage of 2 V.
    Sensors, 2009 IEEE; 11/2009
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Self-aligned growth of ultra-short single-walled carbon nanotubes (SWNTs) was realized by utilizing optical near-field effects in a laser-assisted chemical vapor deposition (LCVD) process. By introducing the optical near-field effects, bridge structures containing single suspended SWNT channels were successfully fabricated through the LCVD process at a relatively low substrate temperature. Raman spectroscopy and I-V analyses have been carried out to characterize the SWNT-bridge structures. Numerical simulations using a high-frequency structure simulator revealed that significant enhancement of local heating occurs at metallic electrode tips under laser irradiation; it is about one order of magnitude higher than that in the rest of the electrodes. This technique suggests a novel approach to in situ low-temperature fabrication of SWNT-based devices in a precisely controlled manner, based on the nanoscale heating enhancement induced by the optical near-field effects.
    Nanotechnology 02/2009; 20(2):025601. DOI:10.1088/0957-4484/20/2/025601 · 3.82 Impact Factor

Publication Stats

5k Citations
562.53 Total Impact Points


  • 1989-2013
    • University of Nebraska at Lincoln
      • Department of Physics and Astronomy
      Lincoln, Nebraska, United States
  • 2001
    • Icahn School of Medicine at Mount Sinai
      Manhattan, New York, United States
  • 2000
    • Institute of Occupational Safety and Health, Taiwan
      T’ai-pei, Taipei, Taiwan
  • 1994-2000
    • National Defense Medical Center
      • Department of Public Health
      T’ai-pei, Taipei, Taiwan
  • 1999
    • Tri-Service General Hospital
      T’ai-pei, Taipei, Taiwan
  • 1998
    • National Defense University, Taiwan
      Taoyuan City, Taiwan, Taiwan
  • 1997
    • National Institute of Standards and Technology
      • Quantum Electronics and Photonics Division
      GAI, Maryland, United States
    • Academia Sinica
      • Institute of Physics
      T’ai-pei, Taipei, Taiwan
  • 1982-1988
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States
  • 1987
    • Montana State University
      • Department of Physics
      Бозмана, Montana, United States