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- 저자 : Kieu Xuan Hau (검색결과 5 건)
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Thanh, Tran Dang,Xuan Hau, Kieu,Huyen Yen, Pham Duc,Manh, T. V.,Yu, S. C.,Phan, T. L.,Telegin, A.,Telegin, S.,Naumov, S. IEEE 2018 IEEE transactions on magnetics Vol.54 No.11
<P>In this paper, we present a detailed analysis on the critical behavior of La<SUB>1.2</SUB>Sr<SUB>1.8</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB> single crystal via isothermal magnetization measured at different temperatures around the paramagnetic–ferromagnetic phase transition at <TEX>$T_{C} = 85$</TEX> K. Using the Landau–Lifshitz coefficients, the Arrott plots ( <TEX>$H/M = a(T) + b(T)M^{2}$</TEX>) of sample have been analyzed. It showed that a(T) changed from positive to negative values at different temperatures in the field ranges of <TEX>$H = 0$</TEX>–10, 10–30, and 30–50 kOe, indicating that the critical behavior could not be described with a single model under different applied fields. Through the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, we determined the values of the critical exponents for La<SUB>1.2</SUB>Sr<SUB>1.8</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB> around its magnetic phase transition over different magnetic field ranges. The critical exponent <TEX>$\beta $</TEX> value is found to be 0.501, 0.417, and 0.371 under field ranges of <TEX>$H = 0$</TEX>–10, 10–30, and 30–50 kOe, respectively. This means that the <TEX>$\beta $</TEX> value depends strongly on the strength of the applied field, shifting from the value approaching that of the mean field model ( <TEX>$\beta = 0.5$</TEX>) to the 3-D-Heisenbeg model ( <TEX>$\beta = 0.365$</TEX>). Meanwhile, its <TEX>$\gamma $</TEX> value is quite stable ( <TEX>$\gamma =0.973$</TEX>–1.074), almost independent on the choice of field fitting range. In addition, using the reduced temperature <TEX>$\varepsilon = (T-T_{C}$</TEX>)/ <TEX>$T_{C}$</TEX> and the obtained critical exponents, almost <TEX>$M(H, T$</TEX>) data measured near <TEX>$T_{C}$</TEX> obey the scaling equation <TEX>$M(H, \varepsilon) = \varepsilon ^{\boldsymbol {\beta }}f_{\pm }(H/\varepsilon ^{\boldsymbol {\beta +\gamma }}$</TEX>), where <TEX>$f_{+}$</TEX> and <TEX>$f_{-}$</TEX> are regular analytic functions corresponding to data at <TEX>$T > T_{C}$</TEX> and <TEX>$T < T_{C}$</TEX>, respectively.</P>
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Thanh, Tran Dang,Huyen Yen, Pham Duc,Hau, Kieu Xuan,Bau, Le Viet,Yu, S. C. IEEE 2018 IEEE transactions on magnetics Vol.54 No.11
<P>In this paper, we have investigated the critical properties in the vicinity of the ferromagnetic (FM)–paramagnetic (PM) phase transition in a polycrystalline sample of La<SUB>0.75</SUB>Ca<SUB>0.2</SUB>Ag<SUB>0.05</SUB>MnO<SUB>3</SUB>, which was prepared by a solid-state reaction method. Temperature dependence of the inverse of the susceptibility <TEX>$\chi ^{-1}$</TEX> ( <TEX>$T$</TEX>) proves an existence of the Griffiths phase well above Curie temperature ( <TEX>$T_{C} = 230$</TEX> K). Detailed analyses of the isothermal magnetization <TEX>$M$</TEX>( <TEX>$H$</TEX>, <TEX>$T$</TEX>) data reveal the sample exhibiting a second-order magnetic phase transition, and its temperature dependences of the saturation magnetization and the initial susceptibility obey the asymptotic relations. Using the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, the critical parameters ( <TEX>$\beta$</TEX>, <TEX>$\gamma$</TEX>, <TEX>$\delta$</TEX>, and <TEX>$T_{C}$</TEX>) of La<SUB>0.75</SUB>Ca<SUB>0.2</SUB>Ag<SUB>0.05</SUB>MnO<SUB>3</SUB> compound have been estimated. Using these critical exponent values, almost <TEX>$M$</TEX>( <TEX>$H$</TEX>, <TEX>$T$</TEX>) data measured at different temperatures around FM–PM phase transition are collapsed onto two universal curves of <TEX>$M/\vert \varepsilon \vert ^{\boldsymbol {\beta }}$</TEX> versus <TEX>$H/\vert \varepsilon \vert ^{\boldsymbol {\beta }+\boldsymbol {\gamma }}$</TEX> corresponding to the regular functions for <TEX>$T > T_{C}$</TEX> and <TEX>$T < T_{C}$</TEX>, respectively.</P>
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Thanh, Pham Thi,Van Duong, Nguyen,Yen, Nguyen Hai,Ngoc, Nguyen Huy,Lam, Nguyen Mau,Hau, Kieu Xuan,Yu, Seong Cho,Dan, Nguyen Huy ELSEVIER 2018 CURRENT APPLIED PHYSICS Vol.18 No.3
<P>In this work, we investigated the influence of additional compounds of Nd-Cu-Al, Dy-Nb-Al, Dy-Zr-Al and Nb-Cu-Al on coercivity of sintered Nd-Fe-B magnets. The additional nanoparticles with size in the range of 40-80 nm was mixed with the micrometer Nd-Fe-B powder before sintering process. The results show that the coercivity of the sintered Nd-Fe-B magnets can be improved by introducing additional nanoparticles to their grain boundaries. The improvement of the coercivity of the magnets is clearly dependent on composition and fraction of the additional compounds. While the Dy-Nb-Al, Dy-Zr-Al and Nb-Cu-Al compounds degrade the coercivity of the sintered Nd-Fe-B magnets, the Nd-Cu-Al nanoparticles considerably improve this quantity. The coercivity the sintered Nd16.5Fe77B6.5 magnets has been enhanced about 40% by adding 3 wt% of the Dy-free compound of Nd40Cu30Al30. (C) 2017 Elsevier B.V. All rights reserved.</P>
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Yen, Nguyen Hai,Thanh, Pham Thi,Koledov, Victor V.,Kamantsev, Alexander P.,Mashirov, Alexey V.,Thanh, Tran Dang,Hau, Kieu Xuan,Yu, Seong Cho,Dan, Nguyen Huy IEEE 2018 IEEE transactions on magnetics Vol.54 No.6
<P>In this paper, we investigated the influence of annealing conditions on magnetic properties, magnetocaloric effect, and critical parameters of Ni<SUB>50</SUB>Mn<SUB>50−<I>x</I></SUB>Sn<SUB><I>x</I></SUB> ( <TEX>$x = 13$</TEX>, 13.5, and 14) alloy ribbons prepared by using the melt-spinning method. The ribbons were annealed at 1123 K for various times. A martensitic–austenitic (M–A) structural phase transformation was observed on both the as-quenched and annealed samples. Temperature of the M–A phase transition ( <TEX>$T_{M-A}$</TEX>) of the ribbons can be regulated in room temperature region by changing the annealing time. Maximum positive and negative magnetic entropy changes, <TEX>$\vert \Delta S_{m}\vert _{\mathrm {max}}$</TEX>, larger than 3 and 1 <TEX>$\text {J}\cdot \text {kg}^{-1}\cdot \text {K}^{-1}$</TEX>, respectively, were achieved on the Ni<SUB>50</SUB>Mn<SUB>37</SUB>Sn<SUB>13</SUB> sample after annealing for 0.5 h. Critical parameters were determined to elucidate magnetic orders in the alloy. The obtained parameters are very close to those of the mean field theory of long-range ferromagnetic orders.</P>
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Pham Thi Thanh,Nguyen Van Duong,Nguyen Hai Yen,Nguyen Huy Ngoc,Nguyen Mau Lam,Kieu Xuan Hau,유성조,Nguyen Huy Dan 한국물리학회 2018 Current Applied Physics Vol.18 No.3
In this work, we investigated the influence of additional compounds of Nd-Cu-Al, Dy-Nb-Al, Dy-Zr-Al and Nb-Cu-Al on coercivity of sintered Nd-Fe-B magnets. The additional nanoparticles with size in the range of 40e80 nmwas mixed with the micrometer Nd-Fe-B powder before sintering process. The results show that the coercivity of the sintered Nd-Fe-B magnets can be improved by introducing additional nanoparticles to their grain boundaries. The improvement of the coercivity of the magnets is clearly dependent on composition and fraction of the additional compounds. While the Dy-Nb-Al, Dy-Zr-Al and Nb-Cu-Al compounds degrade the coercivity of the sintered Nd-Fe-B magnets, the Nd-Cu-Al nanoparticles considerably improve this quantity. The coercivity the sintered Nd16.5Fe77B6.5 magnets has been enhanced about 40% by adding 3 wt% of the Dy-free compound of Nd40Cu30Al30.
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