Soon Cheon Byeon

University of Alabama, Tuscaloosa, AL, United States

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Publications (19)28.02 Total impact

  • Soon Cheon Byeon, A. Misra, P.B. Visscher, W.D. Doyle
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    ABSTRACT: Inverted hysteresis loops in a sputtered FeCo/Ru/FeCo bilayer have been investigated. A Stoner-Wohlfarth energy minimization calculation reproduced the negative remanence assuming a small misalignment of the easy axes of the ferromagnets. During the initial stage of the growth of the top layer, the external field fails to overcome the strong antiferromagnetic exchange coupling between the layers. The magnetizations, as a result, are no longer collinear and the easy axis of the top layer will vary with its thickness. The negative remanence disappeared following an annealing of the sample in a strong field confirming the theory.
    IEEE Transactions on Magnetics 08/2004; · 1.42 Impact Factor
  • S.C. Byeon, A. Misra, W.D. Doyle
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    ABSTRACT: Synthetic antiferromagnetically coupled films have been studied for soft underlayers for perpendicular media. Initially, FeCo bilayers were prepared by dc magnetron sputtering with a structure of glass-Ru(2.5 nm)-FeCo(t<sub>F</sub>)-Ru(t<sub>Ru</sub>)-FeCo(t<sub>F</sub>)-Ru (10 nm), where t<sub>F</sub> was varied from 5 to 200 nm and t<sub>Ru</sub> from 0.2 to 1.4 nm. The antiferromagnetic coupling showed a maximum at t<sub>Ru</sub>=0.6-1.0 nm as expected, depending on t<sub>F</sub>. However, the surface coupling energy J<sub>AF</sub> decreased very rapidly with t<sub>F</sub> from 2.8 erg/cm<sup>2</sup> at t<sub>F</sub>=5 nm to 0.6erg/cm<sup>2</sup> at t<sub>F</sub>=10 nm. A structure of glass-Ru(2.5 nm)-FeCo(50 nm)-Ru(1.0 nm)-FeCo(55 nm)-Ru (10 nm) showed nearly zero remanence and very well separated hysteresis segments at ±30 Oe along the FeCo easy axis and a single narrow hysteresis loop with coercivity of 3.5 Oe along the hard axis. These characteristics were thermally stable up to at least 200°C, which is superior to IrMn exchange-biased systems. Further optimization was achieved with a trilayer structure of glass-Ru(2.5 nm)-FeCo(25 nm)-Ru(1.0nm)-FeCo(45nm)-Ru(1.0 nm)-FeCo(25 nm)-Ru (10 nm).
    IEEE Transactions on Magnetics 08/2004; · 1.42 Impact Factor
  • Source
    Soon Cheon Byeon, Fenglin Liu, G.J. Mankey
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    ABSTRACT: High moment epitaxial Fe-N films were produced using reactive sputtering in an ultra clean sputtering system with in-situ RHEED, and the effects of nitrogen concentration and annealing on magnetic and structural properties were investigated. A sulfur-passivated GaAs substrate was annealed at 450°C to get a good RHEED pattern. A 1 nm thick Fe seed layer was then deposited to promote epitaxial growth of a 20 nm thick Ag(100) buffer layer. Fe-N films were grown on these Ag(100) buffer layers. Nitrogen partial pressure and annealing temperature was varied to obtain epitaxial high moment films. Epitaxial GaAs(001)/1 nm Fe/20 nm Ag(001)/40 nm Fe-N(001)/Ru 10 nm films with low nitrogen concentration exhibited an α'-FeN single phase with a magnetization of about 18 kG. Films with high nitrogen concentration exhibited a mixture of α'-FeN and γ'-Fe<sub>4</sub>N phases, resulting in low magnetization. Post-annealing of films with low nitrogen concentration increased the magnetization up to 20 kG, but the post-annealing of films with high nitrogen concentration increased the amount of the γ'-Fe<sub>4</sub>N phases, resulting in lower magnetization. For films with low nitrogen concentration, sharp RHEED streaks are observed and this is an indication of well-ordered smooth epitaxial films. For films with high nitrogen concentration RHEED streaks are broadened and the background increases which is indicative of an increasing amount of disorder and roughness or possibly a multiphase film. Rms surface roughness of the films was in the range of 0.2-0.6 nm
    IEEE Transactions on Magnetics 08/2001; · 1.42 Impact Factor
  • Y. Ding, Soon Cheon Byeon, C. Alexander Jr
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    ABSTRACT: The thermal stability of the anisotropy of FeTiN films has been investigated. The films were prepared by DC reactive sputtering on glass substrates in a N<sub>2</sub>/Ar atmosphere, and the N flow rate, chamber pressure, sputtering power and film thickness were varied. Target-substrate distances of 6.7 cm and 4.1 cm were used. For films sputtered at the normal target-substrate distance of 6.7 cm, the anisotropy of FeTiN films rotated about 90 degrees after a 100°C, 1 hour annealing in the presence of a 300-400 Oe field perpendicular to the original easy axis. When the 4.1 cm target-substrate distance was used, the anisotropy direction was stable with N concentrations of 6 at.% or less in the films. The anisotropy was unstable for higher N concentrations. X-ray data and stress measurements taken as a function of N concentration showed lattice and stress changes coincident with the stability changes. The dependence of the thermal stability of the film anisotropy on target-substrate distance and N flow rate will be presented and possible mechanisms will be discussed
    IEEE Transactions on Magnetics 08/2001; · 1.42 Impact Factor
  • S.C. Byeon, Y. Ding, C. Alexander Jr
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    ABSTRACT: High moment, soft FeTiN thin films were prepared by sputtering and the effects of film thickness, nitrogen concentration and annealing were investigated. It was found that a heated substrate helped to achieve a high moment and soft magnetic properties. Films thicker than 1500 Å deposited with no substrate heating always exhibited stripe domains, resulting in high values of the coercivity and the anisotropy field. Films deposited at elevated substrate temperatures did not have stripe domains for thickness up to 2000 Å. Films with high nitrogen concentration exhibited γ'-(Fe,Ti)<sub>4</sub>N and ε-(Fe,Ti)<sub>3-x</sub>N phases, resulting in low magnetization and higher coercivity. The annealing of films with low nitrogen concentration increased the magnetization, but the annealing of films with high nitrogen concentration induced a gradual phase change from the γ'-(Fe,Ti)<sub>4</sub>N phase to the ε-(Fe,Ti)<sub>3-x</sub>N phase, resulting in lower magnetization. Our experiments confirm the stabilization of the α''-Fe<sub>16 </sub>N<sub>2</sub> phase by incorporation of Ti, but we did not achieve the 24000 Gauss magnetization reported. Films with 5 at% nitrogen showed the highest moment (20000 Gauss) and best soft (H<sub>C</sub>=3 Oe, H <sub>K</sub>=7 Oe) properties. Annealing of (Fe<sub>92</sub>Ti<sub>8 </sub>)<sub>1-x</sub>N<sub>x</sub> (x=7.8 and 8.7) films deposited on glass at 130°C indicated that the anisotropy direction is not stable when annealed at 200°C for 2 h in a transverse magnetic field of 150 Oc
    IEEE Transactions on Magnetics 10/2000; · 1.42 Impact Factor
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    ABSTRACT: In earlier publications it has been shown that the value and direction of the magnetic anisotropy in FeTaN films can be changed by thermal annealing in a dc magnetic field. These films have potential as future write head materials, and this type of instability could pose a problem. In the current work dc and ac annealing experiments have been performed to test the stability of the anisotropy. Our results confirm the model of interstitial-nitrogen-induced anisotropy in the FeTaN films by illustrating that the magnitude of the anisotropy is reduced at higher temperatures, and that the direction of the anisotropy is stable if the time in the switched direction is less than the time required for diffusion of the nitrogen to a different interstitial position. The direction is stable at 100 °C, for square wave magnetic field switching between the easy and hard axes, at frequencies above 500 Hz. The direction is unstable at 100 °C for switching between the hard axes at frequencies less than 5 kHz. © 2000 American Institute of Physics.
    Journal of Applied Physics 06/2000; · 2.21 Impact Factor
  • S. C. Byeon, J. Rantschler, C. Alexander
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    ABSTRACT: The antiferromagnetic–ferromagnetic exchange coupling between IrMn and FeTaN films has been investigated to study the effects of the exchange field on the high frequency response and the thermal stability of the anisotropy field of FeTaN. Ferromagnetic resonance, vibrating sample magnetometer, and torque measurements were used to determine the values of the unidirectional exchange bias field Hp, the uniaxial anisotropy field Hk and the interfacial energy J. Permeameter measurements to 3 GHz were used to study the effect of the exchange field on the low-frequency permeability and the high-frequency cutoff. Measurements on varying thicknesses of IrMn and FeTaN films gave Hp values from 4 to 115 Oe, Hk values from 10 to 20 Oe, Hc values from 10 to 20 Oe, and an interfacial energy J=0.075 ergs/cm2. The exchange coupling was found to have significant effects on the permeability and the thermal stability of the anisotropy. © 2000 American Institute of Physics.
    Journal of Applied Physics 04/2000; 87(9):5867-5869. · 2.21 Impact Factor
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    ABSTRACT: A systematic variation in linewidth with Co concentration at the X band (9.38 GHz) was observed in polycrystalline Co-substituted NiZnCu ferrites. Also, the temperature dependence of the linewidth and complex permeability were measured for two different Co concentrations. The linewidth shows a minimum with Co concentration. The contribution of porosity, magnetic anisotropy, and eddy current to line broadening was calculated. The line broadening due to eddy current was negligible and the line broadening due to porosity and magnetic anisotropy explain well the variation of linewidth with Co concentration. The temperature at which the linewidth increases rapidly increases with Co concentration. This temperature is consistent with the temperature of the second maximum peak in the temperature dependence of permeability. Therefore, the rapid increase in linewidth with temperature is attributed to the rapid increase in magnetocrystalline anisotropy of divalent cobalt ions. © 2000 American Institute of Physics.
    Journal of Applied Physics 04/2000; 87(9):6220-6222. · 2.21 Impact Factor
  • Soon Cheon Byeon, Hae June Je, Kug Sun Hong
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    ABSTRACT: The application potential of dc electric fields to promote and optimize the ferrite bonding between single- and polycrystalline manganese-zinc ferrite was investigated. The ferrite bonding process was accelerated under the application of a dc electric field. The degree of bonding increased as the bonding time and bonding temperature were increased. It was also found that the direction of an applied current from the poly- to single-crystalline ferrite regions enhances bonding.
    IEEE Transactions on Magnetics 02/2000; · 1.42 Impact Factor
  • Soon Cheon Byeon, Kug Sun Hong
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    ABSTRACT: Bonding between oxide ceramics using an electric field is reviewed. There is a general prerequisite for an effective bonding by an electric field. Only cations should be moved effectively by an applied electric field. If anions can be transported effectively by an applied electric field bonding does not occur. Near the anode lattice was annihilated and near the cathode lattice was created. The microstructure near anode is significantly different from that near cathode. For a given temperature, bonding between manganese–zinc ferrites was accelerated with the application of an electric field. The degree of bonding increased remarkably as the bonding time and bonding temperature increased. Moreover, the direction of an applied current should be from the poly- to single-crystalline ceramics regions in order to enhance bonding effectively. These phenomena can be applied to the preparation of large single crystal cost effectively. Above 1100°C the effect of electric field was not obvious due to thermally activated self-motion of atoms. Bonding between manganese–zinc ferrites improved with increased oxygen partial pressure. This was attributed to the higher diffusion coefficient of the cations at higher oxygen partial pressures.
    Materials Science and Engineering: A. 01/2000;
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    ABSTRACT: Iron deficient compositions of (Ni<sub>0.2</sub>Cu<sub>0.2</sub>Zn <sub>0.6</sub>)<sub>1.02x</sub>Co<sub>x</sub>Fe<sub>1.98</sub>O<sub>4 </sub> (0&les;x&les;0.05) were prepared to investigate their initial permeability dependence on cobalt contents. Extrinsic factors such as grain size and sintered density change little in samples sintered at 900°C, so their effects on permeability can be neglected. Intrinsic factors such as saturation magnetization, magnetocrystalline anisotropy (K<sub>1</sub>) and magnetoelastic anisotropy (K<sub>σ</sub>) can not account for the variation of initial permeability with Co content. Measurement of thermoelectric power shows that the concentration of cation vacancies increases with Co content. Therefore, the local induced anisotropy increases by the ordering of Co ions via increased cation vacancy concentration. This increase in induced anisotropy results in the decrease of initial permeability
    IEEE Transactions on Magnetics 10/1999; · 1.42 Impact Factor
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    ABSTRACT: We have made a comparative microstructural study of field annealed Co95−xFe5(BSi)x amorphous alloys using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Until recently, it was generally assumed that amorphous magnetic alloys respond to field annealing by a process of local directional ordering which leaves the amorphous structure intact. However, striking differences in the microstructural morphology after field annealing were revealed for different glass former ratios B/Si. For high B/Si ratios, the surface crystals are predominantly fcc Co and demonstrate a high density of oxygen faults. For low B/Si ratios, the surface crystals are predominantly hcp Co and almost free of faults. Response to field annealing is proportional to the B/Si ratio and correlates with the presence of oxygen faults in surface crystals. These observations appear to be related to those of Nesbitt and Heidenreich (E.A. Nesbitt, R.D. Heidenreich, J. Appl. Phys. 30 (1959) 1000–1003) in perminvar alloys where oxygen was found to be necessary for field annealing to be effective.
    Materials Science and Engineering B 05/1999; · 1.85 Impact Factor
  • Soon Cheon Byeon, Kug Sun Hong, In-Tae Kim
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    ABSTRACT: A systematic variation in line width at X band (9.78 GHz) with oxygen partial pressure was observed in Mn <sub> 0.47 </sub> Zn <sub> 0.47 </sub> Fe <sub> 2.06 </sub> O <sub> 4 </sub> polycrystalline samples. The linewidth of the samples increased from 105 to 188 Oe with decreasing atmospheric parameters from 8.4 to 6.4. It was found that contribution of anisotropy and porosity to the linewidth was small compared to the variation in linewidth with oxygen partial pressure. Estimation of the Fe <sup> 2+ </sup> concentration of samples by measuring their thermoelectric power revealed that an increase in the concentration from 1.88 to 2.44 wt % was accompanied by decreasing oxygen partial pressure. As the resistivity of grain does not vary with oxygen partial pressure, the contribution of eddy current will be the same irrespective of the oxygen partial pressure. Therefore, the systematic increase in linewidth observed in our present study was attributed to the increase in Fe <sup> 2+ </sup> concentration with decreasing oxygen partial pressure. © 1998 American Institute of Physics.
    Journal of Applied Physics 07/1998; · 2.21 Impact Factor
  • S. C. Byeon, T. Y. Byun, K. S. Hong
    Journal of Materials Research - J MATER RES. 01/1998; 13(11):3191-3196.
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    ABSTRACT: In our present study, the origin of the increase in resistivity of polycrystalline Mn0.47Zn0.47Fe2.06O4 with increasing oxygen partial pressure was investigated by measuring thermoelectric power and electrical resistivity, and through analysis of grain size. The ferrous ion (Fe2+) concentration of the samples was estimated using the thermoelectric power data and it indicated that the increase of oxygen partial pressure accompanied only a 0.5 wt. % decrease in the concentration of Fe2+. The decrease in Fe2+ concentration failed to explain the order of magnitude increase in resistivity. Preferential oxidation of the grain boundaries did not contribute to the increase in resistivity since all the samples were cooled under the same conditions, i.e., constant oxidation potential. Impedance spectroscopy revealed that the increase in resistivity arose from the increase in resistivity of the grain boundary; this is discussed in terms of the microscopic shape factor, the brick-layer model, and the Maxwell–Wagner model. It is suggested that the increase in resistivity, with increasing oxygen partial pressure, originates from the increase in the microscopic shape factor of the grain boundary. © 1997 American Institute of Physics.
    Journal of Applied Physics 06/1997; 81(12):7835-7841. · 2.21 Impact Factor
  • S.C. Byeon, K.S. Hong, H.J. Je
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    ABSTRACT: A systematic variation in initial permeability with oxygen partial pressure during post sintering cooling was observed in Mn0.47Zn0.47Fe2.06O4 polycrystalline samples. The initial permeability increased from 6300 to 8600 when the atmospheric parameter decreased from 8.4 to 6.4. Here atmospheric parameter is the degree of oxygen partial pressure engaged in the cooling stage of the sample preparation. The origins of this systematic variation were investigated by measuring the saturation magnetization under high fields (10 kOe) and by observing microstructure changes as well as the magnetic properties under small applied fields (0.15 mOe). It was found that saturation magnetization of samples under high fields was almost unchanged in the range of oxygen partial pressures through which Fe2+ concentration varied by up to 0.5%. The systematic changes in saturated magnetization and saturation time under small applied fields suggest that the permeability is strongly dependent on domain mobility. This increase in domain mobility was attributed to increased grain growth with decreasing oxygen partial pressure.
    Materials Research Bulletin 05/1997; 32(5):579–588. · 1.97 Impact Factor
  • Soon Cheon Byeon, Hae June Je, Kug Sun Hong
    Japanese Journal of Applied Physics 01/1997; 36:5103-5108. · 1.07 Impact Factor
  • Japanese Journal of Applied Physics 01/1996; 35:3553-3558. · 1.07 Impact Factor
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    ABSTRACT: The interface reactions between Mn-Zn ferrite single crystals and SiO2-PbO-ZnO-MnO systems were investigated using a scanning electron microscope, an electron probe microanalyzer, and an X-ray diffractometer. No intermediate phase was formed at the interface after reaction at 1000 degrees C, but the concentration profiles of Zn and Mn ion at the ferrite adjacent to the interface were markedly affected by their atomic ratio in the glass. When 6 mol% MnO and 4 mol% ZnO, the ratio of which was similar to that in the ferrite, were added to the SiO2-PbO binary system, the concentration of Zn ion was increased at the ferrite adjacent to the interface. It was confirmed that the diffusion rate of Mn ion in the glass melt was higher than that of Zn ion. Therefore, the enrichment of Zn ions was considered to be caused by the higher dissolution rate of Mn ion into the glass from the ferrite than that of Zn ion. It was found that when 7 mol% MnO and 3 mol% ZnO, the ratio of which was higher than that in the ferrite, were contained in the glass, the concentrations of Zn and Mn ions hardly changed at the ferrite adjacent to the interface.
    Japanese Journal of Applied Physics 01/1996; 35(6A):3553-3558. · 1.07 Impact Factor

Publication Stats

70 Citations
28.02 Total Impact Points

Institutions

  • 2000–2004
    • University of Alabama
      • Department of Physics and Astronomy
      Tuscaloosa, AL, United States
  • 1997–2000
    • Seoul National University
      • Department of Materials Science and Engineering
      Seoul, Seoul, South Korea
    • Korea Institute of Science and Technology
      Sŏul, Seoul, South Korea
  • 1999
    • Massachusetts Institute of Technology
      • Department of Materials Science and Engineering
      Cambridge, MA, United States