T.H. Noh

Andong National University, Antō, North Gyeongsang, South Korea

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Publications (48)66.74 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of Zn-phosphate coating on the magnetic properties of Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloy powder cores have been investigated. The Zn-phosphate coating provided good electrical insulation between the magnetic particles through formation of an oxide and other compounds on their surfaces. The consolidated magnetic cores with powders treated in the solution of pH = 1.3 acidity exhibited a permeability of 45, persisting up to about 2 MHz and a core loss of 500 mW/cm3 at the frequency of 50 kHz under the induction of Bm = 0.1 T. Furthermore, 62% permeability at 50 Oe of dc bias field was obtained. From these results, it was considered that the Zn-phosphate coating could be an effective method to form an efficient insulating coat even for small-sized Fe73.5Cu1Nb3Si15.5B7 nanocrystalline alloy powders.
    Journal of Applied Physics 04/2006; 99(8):08F113-08F113-3. DOI:10.1063/1.2173611 · 2.19 Impact Factor
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    ABSTRACT: Dust cores (compressed powder cores) of alloy with a size of in diameter have been prepared by phosphate coatings and annealings at for 1 h in nitrogen atmosphere. Further the magnetic and mechanical properties of the powder cores were investigated. As a general trends, the compressive strength and core loss decreased with the increase in annealing temperature. When annealed at , the compressive strength was 15 kgf, the permeability and quality factor were 74 and 26, respectively. Moreover the core loss at 50 kHz and 0.1 T induction was , and the percent permeability under the static field of 50 Oe was estimated to be about 78. In addition, the cut-off frequency in the cure representing the frequency dependence of effective permeability was measured to be around 200 kHz. These properties of the alloy dust cores could be considered to be due to the good insulation effect of iron-phosphate coats, the decrease in magnetocrystalline anisotropy and saturation magnetostriction and the increase in electric resistivity.
    01/2005; 15(5). DOI:10.4283/JKMS.2005.15.5.270
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    T.H. Noh, H.Y. Choi
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    ABSTRACT: In the fabrication process of Fe-based amorphous alloy powder cores by pulverization of the melt-spun ribbons and cold compaction, the effects of powder preparation method on the magnetic & electric properties, powder shapes and microstructure of cores have been investigated. The powder cores made by using rotor mill showed low effective permeability as compared to the cores prepared by ball milling. However the frequency dependence and quality factor properties were superior in the case of rotor-milling. Further the powders prepared by rotor mill had homogeneous and round shapes through strong shearing in the sieve ring, while the ball milled powders were inhomogeneous and relatively small. The lower permeability of the powder cores fabricated with rotor mill was considered to be due to the high internal stress occurred by very intensive shearing. Moreover the powder cores produced by rotor-milling showed lower core loss and good frequency dependence of effective permeability possibly due to the higher electrical insulation between magnetic particles. The dc bias property of the powder cores made by rotor-milling was better than the one by ball-milling.
    01/2005; 15(3). DOI:10.4283/JKMS.2005.15.3.191
  • HY Choi, S. J. Ahn, T. H. Noh
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    ABSTRACT: The relationship between magnetic properties and particle size in nanocrystalline Fe73.5Cu1Nb3Si15.5B7 alloy powder cores prepared by using a rotor mill and cold press was investigated. The powder cores having large particles of 250-850 m exhibited stable permeability of 100 up to 500 kHz, a maximum level of 50 of quality factor at 50 kHz, and 360 mW/cm3 core loss at 50 kHz and 0.1 T of induction. However the powder cores with small particles lower than 250 m showed low permeability and high core loss as compared to large particle cores. Additionally the large particle cores have homogeneous and well-aligned microstructure leading to high density state. On the contrary, the powder cores composed of small magnetic particles showed irregular and complex distribution of magnetic powders, and the density seems rather low. The enhanced magnetic properties of powder cores with large particles were attributed to the particle size dependence of compressed state of powders.
    physica status solidi (a) 06/2004; 201(8):1879-1882. DOI:10.1002/pssa.200304551 · 1.21 Impact Factor
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    T.H. Noh, H.Y. Choi
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    ABSTRACT: The variation of magnetic properties with insulating materials(glass frits, talc and polyamide) in compressed powder cores composed of Fe73.5/CuNbSi15.5/B7/ nanocrystalline alloy powders(size: 250~850 ) and 3 wt% insulators has been investigated. Larger permeability was obtained at the frequency lower than 300~400 kHz for the powder cores including ceramic insulators(glass frits and talc) as compared to the cores with polyamide, while at higher frequency than 1 MHz the permeability of the former cores decreased rapidly. Further the cores with ceramic insulators showed larger core loss and smaller peak quality factor attained at lower frequency. On the contrary, the powder cores with polyamide exhibited high stability of permeabilities up to several MHz and superior core-loss and quality-factor properties. Moreover the dc bias property was better in the wide field range for the cores having polyamide. The enhanced magnetic properties of polyamide-added cores were attributed to the more sufficient electrical insulation between magnetic particles, where the higher insulation state was considered to be obtained from the larger volume fraction of polyamide in the powder cores.
    01/2004; 14(5). DOI:10.4283/JKMS.2004.14.5.186
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    T.H. Noh, H.Y. Choi, S.J. Ahn
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    ABSTRACT: The annealing-temperature dependence of magnetic properties in compressed powder cores being composed of ball-milled F C N S alloy powders (size 250∼850) and 5 wt% of ceramic insulators has been investigated. When annealed at 5 for 1 h and so transformed to -Fe phase nanocrystalline structure with the grain size of 11 nm (electrical resistivity : 110 Ωcm), the highest effective permeability of 125 and quality factor of 53 were obtained, and the permeability persisted up to about 500 KHz. Further the core loss measured at the frequency of 50 KHz and the induction amplitude of 0.1 T was very low (230 mW/㎤). However the dc bias characteristics was not satisfactory as compared to that of conventional powder core materials(MPP, Sendust etc.). The inferior dc bias property of F C N S alloy powder cores was attributed to the fact that the size of powder was too large for obtaining the same permeability with that of conventional materials.terials.
    01/2004; 14(1). DOI:10.4283/JKMS.2004.14.1.007
  • G. H. Kim, T. H. Noh, G. B. Choi, KY Kim
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    ABSTRACT: Cold-pressed nanocrystalline powder cores were fabricated using powders of nanocrystalline ribbons which were ball milled for short time. Their magnetic properties at high frequency were measured. The powder size ranges from 20 to 850 μm and the contents of the glass binder are between 1 and 8 wt %. For cores composed of large particles of 300–850 μm with 5 wt % glass binder, we obtained a stable permeability of 100 up to 800 kHz, a maximum level 31 of quality factor at frequency of 50 kHz, and 320 mW/cm3 core loss at f=50 kHz and Bm=0.1 T. This is mainly due to the good soft magnetic properties of the powders and the higher insulation of powder cores which cause low eddy current losses. © 2003 American Institute of Physics.
    Journal of Applied Physics 05/2003; 93(10):7211-7213. DOI:10.1063/1.1555907 · 2.19 Impact Factor
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    ABSTRACT: Fe–Nb–B–N films with good soft magnetic properties were fabricated by Ar+N2 reactive sputtering. The quaternary films have better soft magnetic properties than that of Fe–Nb–B films. The best magnetic properties are saturation magnetization of 16.5 kG, coercivity of 0.13 Oe and effective permeability of about 5000 up to 10 MHz. It was observed by transmission electron microscopy that the Fe–Nb–B–N thin film annealed at 590 °C consisted of three phases: a fine α-Fe phase whose grain size is around 7 nm, a Nb–B rich amorphous phase and NbN precipitates with the size of less than 3 nm. The fine grained α-Fe structure, together with finely dispersed NbN precipitates and the amorphous boundary phase are considered to be a main factor for the good magnetic properties.
    Journal of Applied Physics 06/1998; 83(11). DOI:10.1063/1.367932 · 2.19 Impact Factor
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    ABSTRACT: Not Available
    MMM-Intermag Conference, 1998. Abstracts., The 7th Joint; 02/1998
  • MMM-Intermag Conference, 1998. Abstracts., The 7th Joint; 01/1998
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    ABSTRACT: Ultrathin Fe<sub>78</sub>Al<sub>4</sub>B<sub>12</sub>Nb<sub>5</sub>Cu<sub>1</sub> and Fe<sub>83</sub>B<sub>9</sub>Nb<sub>7</sub>Cu<sub>1</sub> nanocrystalline ribbon alloys below 10 μm in thickness were annealed in transverse magnetic field, and then the high-frequency soft magnetic properties and their compositional effect were investigated. Very high effective permeability and excellent magnetic core loss characteristics in MHz range were obtained for both alloys after optimum annealing. However, the Al-added alloy was more sensitive to the magnetic field annealing and much improved soft magnetic properties in the high frequency range were revealed
    IEEE Transactions on Magnetics 10/1997; DOI:10.1109/20.619575 · 1.21 Impact Factor
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    ABSTRACT: Melt-spun Fe<sub>83</sub>B<sub>9</sub>Nb<sub>7</sub>Cu<sub>1</sub> alloy with ultrathin ribbon has been studied with Mossbauer spectroscopy and X-ray diffraction. The enhanced magnetic property of the flash-annealed alloy was attributed to the reduced α-Fe phase grain size to 6 nm and the higher effective permeability and smaller magnetic core loss at 1 MHz than conventional annealed alloys. The occupied area of the nanocrystalline phase at the optimum 773 K is about 73% whereas that for conventional annealing temperature at 893 K is about 71%. The flash annealing technique was effective in improving the high-frequency soft magnetic property of nanocrystalline Fe<sub>83</sub>B<sub>9</sub>Nb<sub>7</sub>Cu<sub>1</sub> alloy
    IEEE Transactions on Magnetics 10/1997; DOI:10.1109/20.619573 · 1.21 Impact Factor
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    ABSTRACT: Melt-spun Fe{sub 83}B{sub 9}Nb{sub 7}Cu{sub 1} alloy with ultrathin ribbon has been studied with Moessbauer spectroscopy and X-ray diffraction. The enhanced magnetic property of the flash-annealed alloy was attributed to the reduced {alpha}-Fe phase grain size to 6 nm and the higher effective permeability and smaller magnetic core loss at 1 MHz than conventional annealed alloys. The occupied area of the nanocrystalline phase at the optimum 773 K is about 73% whereas that for conventional annealing temperature at 893 K is about 71%. The flash annealing technique was effective in improving the high-frequency soft magnetic property of nanocrystalline Fe{sub 83}B{sub 9}Nb{sub 7}Cu{sub 1} alloy.
    IEEE Transactions on Magnetics 08/1997; 33(5Pt2). · 1.21 Impact Factor
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    ABSTRACT: In an effort to obtain soft magnetic materials with excellent high-frequency characteristics, effects of flash annealing on magnetic properties and microstructure in melt-spun Fe-B-Nb-Cu alloy with ultrathin ribbon shape less than 10 μm thickness were investigated. The alloy subjected to optimum annealing treatment showed higher effective permeability and smaller magnetic core loss at 1 MHz than conventionally annealed alloy. The enhanced magnetic properties of the flash-annealed alloy were attributed to the reduced α-Fe phase grain size to 6 nm and the lower remanence ratio of about 0.3 in comparison to the conventionally annealed alloy with the values of 9 nm and 0.7, respectively. The results show that the flash annealing technique was effective in improving the high-frequency soft magnetic properties of Fe-B-Nb-Cu nanocrystalline alloy.
    Materials Science and Engineering A 06/1997; DOI:10.1016/S0921-5093(97)80071-8 · 2.41 Impact Factor
  • Magnetics Conference, 1997. Digests of INTERMAG '97., 1997 IEEE International; 01/1997
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    ABSTRACT: The metal oxides MgO, BaO, Al2O3, SiO2, MgO–Al2O3, CaO–Al2O3, SrO–Al2O3, BaO–Al2O3 and MgO–SiO2 have been coated onto ribbons of the Fe-based amorphous alloy Metglas 2605S3A using a sol–gel process. The effects of the surface coating on the magnetic properties of the alloy are investigated. The d.c. hysteresis loop for ribbons coated with MgO and MgO–Al2O3 is more square shaped than that for the uncoated ribbon. For ribbons coated with BaO, SrO–Al2O3 and BaO–Al2O3 it is more inclined than for the uncoated ribbon. Significant differences in the frequency dependence of the effective permeability are observed that depend on the nature of the coated oxides. The core loss is also affected by the coating. These results may be explained in terms of a stress induced by the coating and the modification of the domain structure via elastic and/or magnetoelastic interactions. It is thought from the magnetoelastic interactions that the MgO and MgO–Al2O3 coatings induce tensile stresses whilst those of BaO, SrO–Al2O3 and BaO–Al2O3 induce compressive stresses.
    Journal of Materials Science 12/1996; 32(12):3219-3225. DOI:10.1023/A:1018615104519 · 2.31 Impact Factor
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    ABSTRACT: The amorphous Fe<sub>84</sub>B<sub>9</sub>Nb<sub>7</sub> and its nanocrystallization have been studied by X-ray, Mossbauer spectroscopy and magnetic moment measurements. The average hyperfine field H<sub>hf </sub>(T) of the amorphous state shows a temperature dependence of [H <sub>hf</sub>(T)-H<sub>hf</sub>(0)]/H<sub>hf</sub>(0)=-0.52 (T/T<sub>C </sub>)<sup>3/2</sup>-0.34 (T/T<sub>C</sub>)<sup>5/2</sup> for T/T<sub>C </sub><0.7 indicative of spin-wave excitation. The quadrupole splitting just above the Curie temperature T<sub>C</sub> is 0.41 mm/s, whereas the average quadrupole shift below T<sub>C</sub> is zero. The Curie and crystallization temperatures are determined to be T<sub>C</sub>=330 K and T<sub>x</sub>=750 K respectively, for a heating rate of 5 K/min. The occupied area of the nanocrystalline phase at the optimum annealing temperature is about 73%
    IEEE Transactions on Magnetics 10/1996; DOI:10.1109/20.539164 · 1.21 Impact Factor
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    ABSTRACT: The magnetic properties of ultrathin Fe<sub>75</sub>Al<sub>4</sub>Nb<sub>5</sub>B<sub>12</sub>Cu<sub>1</sub> nanocrystalline alloy ribbons with 9 μm thickness and the effect of Al additions to Fe-B-Nb-Cu alloy for improving the high-frequency magnetic properties were investigated. It was found that the effective permeability at frequencies over 100 kHz was higher and the core loss was lower for the composition Fe<sub>75</sub>Al<sub>4</sub>Nb<sub>5</sub>B<sub>12</sub>Cu<sub>1</sub> alloy. Moreover, the reduction of the ribbon thickness to 9 μm was very effective in improving their permeability and the core loss characteristics up to the MHz frequency range
    IEEE Transactions on Magnetics 10/1996; DOI:10.1109/20.539166 · 1.21 Impact Factor
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    ABSTRACT: The amorphous Fe{sub 84}B{sub 9}Nb{sub 7} and its nanocrystallization have been studied by x-ray. Moessbauer spectroscopy and magnetic moment measurements. The average hyperfine field H{sub hf}(T) of the amorphous state shows a temperature dependence indicative of spin-wave excitation. The quadrupole splitting just above the Curie temperature {Tc} is 0.41 mm/s. Whereas the average quadrupole shift below {Tc} is zero. The Curie and crystallization temperatures are determined to be {Tc} = 330 K and T{sub x} = 750 K. respectively, for a heating rate of 5 K/min. The occupied area of the nanocrystalline phase at the optimum annealing temperature is about 73%.
    IEEE Transactions on Magnetics 09/1996; 32(5Pt2). · 1.21 Impact Factor
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    ABSTRACT: Amorphous Co80+xTM12B8-x (TM = Ti, Zr, Hf, Nb; x = 0, 2, 4 at%) alloys were prepared by the single-roller melt-spinning technique. The saturation magnetization of the amorphous ribbons was measured by a SQUID and a vibrating sample magnetometer at 5-800 K under an applied field of 10 kOe. Typical thermo-magnetization curves were observed, and average values of the spectroscopic splitting g factor were estimated from the ferromagnetic resonance (FMR) curve. For all the amorphous alloys studied here, the saturation magnetization in the temperature range 5 K up to about 0.3TC can be described by the Bloch relation, Ms(T) = Ms(0)(1 - BT3/2 - CT5/2. The spin wave stiffness constants were calculated from the values of Ms(0), B and the spectroscopic splitting g factor.
    Journal of Magnetism and Magnetic Materials 05/1996; 157:237-238. DOI:10.1016/0304-8853(95)01227-3 · 2.00 Impact Factor

Publication Stats

232 Citations
66.74 Total Impact Points

Institutions

  • 1996–2006
    • Andong National University
      Antō, North Gyeongsang, South Korea
  • 1995–1996
    • Hankuk University of Foreign Studies
      • Department of Chemistry
      Sŏul, Seoul, South Korea
  • 1990–1996
    • Korea Institute of Science and Technology
      Sŏul, Seoul, South Korea
  • 1994
    • Seoul National University
      Sŏul, Seoul, South Korea
  • 1993
    • Chungbuk National University
      • Department of Physics
      Chinch'ŏn, North Chungcheong, South Korea
  • 1989–1992
    • Tohoku University
      • Institute for Materials Research
      Miyagi, Japan