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Journal of magnetics 7건

  1. [국내논문]   Charge Transformation of CU-ions in CuxFe3-xO4 (χ=0.1, 0.2)   피인용횟수: 1

    Lee, Choong Sub (Department of Physics, Pukyong National University ) , Lee, Chan Young (Department of Physics, Pukyong National University ) , Kwon, Dong Wook (Department of Physics, Pukyong National University)
    Journal of magnetics v.7 no.2 ,pp. 25 - 28 , 2002 , 1226-1750 ,

    초록

    Slowly cooled $Cu_xFe_{3-x}O_4$ ( $\chi$ =0.1, 0.1, 0.2) have been investigated over a temperature range from 82 to 700 K using the M $\ddot{o}$ ssbauer technique. X-ray diffraction shows that these have a single-phase cubic spinel structure of lattice parameters $\alpha$ =8.396 a 8.396 and 8.398 ${\AA}$ , respectively. Since Cu ions prefer B (octahedral) sites to A (tetrahedral) sites, the ionic distribution is $(Fe)_A[Fe_{2-x}Cu_x]_BO_4$ . M $\ddot{o}$ ssbauer spectra consisted of two sets of 6-line pattern from. A site in ferric state and B site in ferrous-ferric state. Intensity ratio of B to A subspectra is 1.0 at 82 K and increases to 2.0 at 700 K with increasing temperature. After annealing the samples under vacuum at $450^circ{C}$ for a half hour, x-ray diffraction patterns have the peaks of magnetite- and hematite-phase. Lattice constants of magnetite-phase are 8.395 and 8.392 ${\AA}$ smaller than 8.396 and 8.398 ${\AA}$ before annealing, respectively. M $\ddot{o}$ ssbauer spectra reveal the conventional magnetite pattern with the additional hematite pattern. Intensity ratios of B to A subspectra fur magnetite-phase become 1.9-2.0 over all temperature ranges and Cu ions are distributed over A and B sites randomly. Ratios of hematite to total intensity in M $\ddot{o}$ ssbauer spectra for $\chi$ = 0.1 0.1 and $\chi$ = 0.2 0.2 are 10 and 21%, respectively. These hematite ratios may be due to annealing under vacuum at $450^circ{C}$ , which transforms $Cu^{2+}$ ionic states into $Cu^{1+}$ . Verwey temperatures far $\chi$ = 0.1 0.1 and $\chi$ = 0.2 0.2 are $123\pm2$ K and $128\pm2$ K.

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  2. [국내논문]   A Study of Synthesis of NiCuZn-Ferrite Sintering in Low Temperature by Metal Nitrates and its Electromagnetic Property   피인용횟수: 1

    Kim, Chul Won (Department of Physics, Soong Sil University ) , Koh, Jae Gui (Department of Physics, Soong Sil University)
    Journal of magnetics v.7 no.2 ,pp. 29 - 39 , 2002 , 1226-1750 ,

    초록

    The initial NiCuZn synthetic ferrite were acquired from thermally decomposing the metal nitrates $Fe(NO_3)_39H_2O, Zn(NO_3)_26H_2O, Ni(NO_3)_26H_2O, and Cu(NO_3)_23H_2O$ at $150^circ{C}$ for 24 hours, and then we calcined the synthetic powder at $500^circ{C}$ , pulverized each of those for 3, 6, 9, 12, and 15 hours in a steel ball mill, sintered each at $700^circ{C}$ to $1,000^circ{C}$ for 1 hour, and thus studied their microstructures and electromagnetic properties. We could make the initial specimens chemically bonded in liquidity at a low-temperature $150^circ{C}$ , by using the low melting points less than $200^circ{C}$ of the metal nitrates instead of the mechanical ball-mill pulverization, then narrow a distance between the particles into a molecular one, and thus lower the reaction point of sintering by at least $200^circ{C}$ to $300^circ{C}$ . Their initial permeability was 50 to 400 and their maximum magnetic induction density and coercive force, 2,400 G and 0.3 Oe to 0.5 Oe respectively, which was similar to those of NiZnCu ferrite synthesized in the conventional process. In the graph of initial permeability by frequencies, a $180^circ{C}$ rotation of the magnetic domains which appears in a broad band of micro-wave before and after the resonance frequency, could be perceived.

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  3. [국내논문]   Effects of Ga Substitution in LaFe1-xGaxO3 (χ= 0, 0.1, 0.3, 0.5, and 0.7)  

    Yoon, Sung-Hyun (Department of physics, Gunsan National University ) , Park, Seung-Jin (Department of physics, Gunsan National University ) , Cha, Deok-Joon (Department of physics, Gunsan National University ) , Min, Byung-Ki (Department of physics, Kookmin University ) , Kim, Chul-Sung (Department of physics, Kookmin University)
    Journal of magnetics v.7 no.2 ,pp. 40 - 44 , 2002 , 1226-1750 ,

    초록

    Crystallographic and magnetic properties of ; $LaFe_{1-x}Ga_xO_3$ ( $\chi$ = 0, 0 0, 0.1, 0.3, 0.5, and 0.7) were studied using XRD and Mossbauer spectroscopy. The crystal structures were found to be orthorhombic and the lattice parameters $\alpha$ , b, and c were found to decrease with increasing Ga substitution. M $\ddot{o}$ ssbauer spectra were obtained at various absorber temperatures ranging from 20 K to 750 K. The M $\ddot{o}$ ssbauer spectra were all sextets below $T_N$ and were all singlets above $T_N$ . Asymmetric broadening of the M $\ddot{o}$ ssbauer spectral lines at 20 K was explained by the multitude of possible environments for an iron nucleus. As the temperature increases to $T_N$ , a systematic line broadening in M $\ddot{o}$ ssbauer spectra was observed and interpreted to originate from different temperature dependencies of the magnetic hyperfine fields at various iron sites.

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  4. [국내논문]   A Study of Magnetic Field Annealing on Microstructures and Magnetic Properties of Nanocomposite Sm-Co/Co Films  

    Yang, Choong-Jin (Electromagnetic Materials Laboratory, Research Institute of Industrial Science and Technology (RIST) ) , You, Cai-Yin (Institute of Metal Research, Academia Sinica, Electromagnetic Materials Laboratory, Research Institute of Industrial Science and Technology (RIST) ) , Zhang, Z.D. (Institute of Metal Research, Academia Sinica ) , Kim, Kyung-Soo (Electromagnetic Materials Laboratory, Research Institute of Industrial Science and Technology (RIST) ) , Han, Jong-Soo (Electromagnetic Materials Laboratory, Research Institute of Industrial Science and Technology (RIST))
    Journal of magnetics v.7 no.2 ,pp. 45 - 50 , 2002 , 1226-1750 ,

    초록

    A magnetic field annealing is firstly used for nanostructured Sm-Co/Co films, prepared by magnetron sputtering method. The effects of magnetic field annealing on single-layered Sm-Co films are different from those on multi-layered Sm-Co/Co films. A detailed analysis of microstructures and magnetic properties is made by means of HRTEM, Auger electron spectroscopy, XRD and Physical Property Measurement System (PPMS). From magnetic properties and microstructure analysis, it was confirmed that these differences originate from the effects of magnetic field annealing on crystallization behavior of the films. The relationship between magnetic properties and microstructures explains a different demagnetization process of single-layered and multilayered films. For the single-layered Sm-Co films, magnetic-field-annealing makes the main phases change from $CaCu_5/ to Zn_2Th_{17}$ structure, resulting in a decrease of coercivity. The results show that the magnetic-field-annealing is useful to improve the properties of nanostructured Sm-Co(30 nm)/Co(10 nm) films, which ascribe to improving the pinning effectiveness in coercivity mechanism and decreasing the magnetostatic interaction of films. A very high coercivity about 0.7 T was obtained from nanoscaled multi-layered Sm-Co(30 nm)-/Co(10 nm) films.

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  5. [국내논문]   Crystallization of Ba-ferrite/sapphire(001) Thin Films Studied by Real-Time Synchrotron X-ray Scattering  

    Cho, Tae-Sik (Department of Materials Science and Engineering, Sangju National University)
    Journal of magnetics v.7 no.2 ,pp. 51 - 54 , 2002 , 1226-1750 ,

    초록

    The crystallization of amorphous Ba-ferrite/sapphire(001) thin films was studied in real-time synchrotron x-ray scattering experiments. In the sputter-grown amorphous films, we found the existence of epitaxial $Fe_3O_4$ interfacial crystallites (50- ${\AA}$ -thick), well aligned $[0.03^circ$ full-width at half-maximum (FWHM)] to the sapphire [001] direction. The amorphous precursor was crystallized to epitaxial Ba-ferrite and \alpha-Fe_2O_3$ grains in two steps; i) the nucleation of crystalline \alpha-Fe_2O_3$ phase started at $300^circ{C}$ together with the transformation of the $Fe_3O_4$ crystallites to the \alpha-Fe_2O_3$ crystallites, ii) the nucleation of Ba-ferrite phase occurred at temperature above $600^circ{C}$ . In the crystallized films irrespective of the film thickness, the crystal domain size of the \alpha-Fe_2O_3$ grains was about 250 ${\AA}$ in the film plane, similar to that of the Ba-ferrite grains.

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  6. [국내논문]   Micromagnetic Modeling of Spin-valve MR Head with Synthetic Antiferromagnet (SyAF)  

    Tahk, Y.W (Dep. of Materials Sci. and Eng., Korea Advanced Institute of Science and Technology ) , Lee, K.J (Storage Lab. Samsung Advanced Institute of Technology ) , Lee, T.D (Dep. of Materials Sci. and Eng., Korea Advanced Institute of Science and Technology)
    Journal of magnetics v.7 no.2 ,pp. 55 - 58 , 2002 , 1226-1750 ,

    초록

    MR transfer behaviors of the permanent magnet biased spin valve MR sensors with SyAF (synthetic antiferromagnet) layers were studied by micromagnetics modeling. For narrow track MR heads, various height to width ratios were considered together with strength of permanent magnets which stabilities the free layed As the MR sensor width is reduced to $0.12 \mu{m}$ , sensor height less than 0.09 ${\mu}{\textrm}{m}$ is needed to show good linearity and the Mr.t of permanent magnets smaller than 0.2 memu/ $cm^2$ is sufficient for the domain stabilization. The conditions for single domain behavior of the free layer were also investigated through optimizing the biasing strength of permanent magneto the shield gap and the aspect ratio of MR sensor.

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  7. [국내논문]   Abnormal Temperature Dependence of Tunneling Magnetoresistance for Magnetic Tunnel Junctions  

    Lee, K.I. (Korea Institute of Science and Technology ) , Lee, J.H. (Korea Institute of Science and Technology ) , Lee, W.Y. (Korea Institute of Science and Technology ) , Rhie, K. (Dept. of Physics, Korea University ) , Lee, B.C. (Dept. of Physics, Inha university ) , Shin, K.H. (Korea Institute of Science and Technology)
    Journal of magnetics v.7 no.2 ,pp. 59 - 62 , 2002 , 1226-1750 ,

    초록

    Magnetic tunnel junctions (MTJs) were fabricated with high bias for plasma oxidation and the effects of annealing on the temperature dependence of tunneling magnetoresistance (TMR) were investigated experimentally. As-grown, TMR increases, peaks around 160 K, and decreases with increasing temperature from 80 K to 300 K. When MTJs are annealed, $T_{max}$ , the temperature at which maximum TMR is obtained, decreases as annealing temperature increases to the optimal point. In order to explain this abnormal temperature dependence of TMR, the difference of conductance between parallel and antiparallel alignments of magnetizations as a function of temperature is also analyzed. The shifts of $T_{max}$ due to annealing process are described phenomenologically with spin-dependent transfer rates of electrons tunnel through the barrier.

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