First-to-second-order magnetic-phase transformation in La_0.7Ca_0.3-xBa_xMnO₃ exhibiting large magnetocaloric effect

Phan, T.L.,Dang, N.T.,Ho, T.A.,Manh, T.V.,Thanh, T.D.,Jung, C.U.,Lee, B.W.,Le, A.T.,Phan, A.D.,Yu, S.C. Elsevier Sequoia 2016 Journal of alloys and compounds Vol.657 No.-

We have prepared polycrystalline samples La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Ba<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0, 0.025, 0.05, 0.075 and 0.1) by solid-state reaction, and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field (M-H-T) measurements. Experimental results reveal the easiness in tuning the Curie temperature (T<SUB>C</SUB>) from 260 to about 300 K by increasing Ba-doping concentration (x) from 0 to 0.1. Under an applied field H = 50 kOe, maximum magnetic-entropy changes around T<SUB>C</SUB> of the samples can be tuned in the range between 6 and 11 J kg<SUP>-1</SUP> K<SUP>-1</SUP>, corresponding to refrigerant-capacity values ranging from 190 to 250 J kg<SUP>-1</SUP>. These values are comparable to those of some conventional MC materials, and reveal the applicability of La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Ba<SUB>x</SUB>MnO<SUB>3</SUB> materials in magnetic refrigeration. Analyses of the critical behavior based on the Banerjee criteria, Arrott plots and scaling hypothesis for M-H-T data prove a magnetic-phase separation when Ba-doping concentration changes. In the doping region x = 0.05-0.075, the samples exhibits the crossover of first- and second-order phase transitions with the values of critical exponents β and γ close to those expected for the tricritical mean-field theory. The samples with x < 0.05 and x > 0.075 exhibit first- and second-order transitions, respectively. More detailed analyses related to the Griffiths singularity, the critical behavior for different magnetic-field intervals started from 10 kOe, and the magnetic-ordering parameter n = dLn|ΔS<SUB>m</SUB>|/dLnH (where ΔS<SUB>m</SUB> is the magnetic-entropy change) demonstrate magnetic inhomogeneities and multicritical phenomena existing in the samples.

Ferromagnetic Resonance of Soft Magnetic CoFeAlO Thin Films

V. S. Dang,T.L. Phan,N.D. Ha,C.O.Kim,S.C. Yu 한국자기학회 2007 한국자기학회 학술연구발표회 논문개요집 Vol.- No.-

Ferromagnetism of MnZnO system doped with Zn₃P₂

V. S. Dang,Y. Y. Song,H. D. Quang,Y. G. Yoo,S. C. Yu 한국자기학회 2006 한국자기학회 학술연구발표회 논문개요집 Vol.16 No.1

Ferromagnetism-to-Paramagnetism Transition in the ZnMnO System

V. S. Dang,Y. Y. Song,N. Q. Hoa,유성초,Y. G. Yoo 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5

The magnetic properties of Mn- and P-doped ZnO prepared by using the solid state reaction and pulsed laser deposition (PLD) were investigated by measuring the magnetization and the absorption derivative of the electron paramagnetic resonance (EPR). The film's thickness was about 0.3 μm. The X-ray diraction pattern indicated a single-phase polycrystalline ZnO structure without any MnO₂ phase in both the polycrystalline samples and the thin lms. The magnetic behaviors of the samples were determined by using an alternating gradient magnetometer (AGM) at room tempera- ture. All the bulk samples showed ferromagnetism at room temperature. Mn-doped ZnO films with Zn₃P₂ added also showed ferromagnetism at room temperature. A transition from ferromagnetism to paramagnetism with increasing in sintering temperature was detected in the EPR experiments. The absorption derivative of the EPR signal showed hyperne splitting for the samples sintered at 800 and 900℃ due to a spin degeneracy of Mn²+, the hyperfine splitting disappeared for the samples sintered at 1000℃ due to a superposition of the six lines of hyperfine splitting.

Structural, Optical and Magnetic Properties of Zn1-xMnxO Thin Films Assembled by Using the CVD Method

V. S. Dang,유성초,판더롱 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5

In our study, Zn1..xMnxO (x = 0, 0.07) thin lms were synthesized on sapphire (0001) substrates by using a chemical vapor deposition (CVD) method. The samples were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Raman-scattering spectroscopy and room-temperature photoluminescence. XRD and Raman spectra showed no sign of a single MnO phase in the ZnO after Mn doping. In Raman- scattering studies, an additional Mn-related vibration mode appeared at 520 and 660 cm..1, which did not appear in the Raman spectra of undoped ZnO. The magnetization M was measured as a function of the static, externally-applied field H at room temperature.

Unusual Critical Behavior in La_1.2Sr_1.8Mn₂O₇ Single Crystal

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>

Magnetic and magnetocaloric properties of Sm_1−xCa_xMnO₃ (<i>x</i> =0.88) nanoparticles

Phan, T.L.,Dang, N.T.,Ho, T.A.,Rhyee, J.S.,Shon, W.H.,Tarigan, K.,Manh, T.V. North-Holland Pub. Co 2017 Journal of magnetism and magnetic materials Vol.443 No.-

<P><B>Abstract</B></P> <P>We used the mechanical milling to prepare orthorhombic Sm<SUB>0.12</SUB>Ca<SUB>0.88</SUB>MnO<SUB>3</SUB> samples with the average crystallite size (<I>d</I>) changing from 100 to 139nm. Their magnetic and magnetocaloric properties were then studied upon magnetization data versus the temperature and magnetic field, <I>M</I>(<I>T</I>, <I>H</I>). The results revealed the samples undergoing the ferromagnetic-paramagnetic (FM-PM) phase transition at the Curie temperature <I>T</I> <SUB>C</SUB> ≈110K. Around this transition, the magnetic-entropy change (Δ<I>S</I> <SUB>m</SUB>) reaches the maxima. The maximum |Δ<I>S</I> <SUB>m</SUB>| values are about 2–4J·kg<SUP>−1</SUP>·K<SUP>−1</SUP>, corresponding to relative cooling power of 35–60J·kg<SUP>−1</SUP>, for an applied field <I>H</I> =30kOe. The assessments based on Banerjee’s criteria and constructing a universal curve for |Δ<I>S</I> <SUB>m</SUB>(<I>T</I>, <I>H</I>)| data indicate the samples having the nature of a second-order phase transition. Also, the detailed analyses based on the Curie-Weiss law and magnetic-order exponent prove the existence of the Griffiths phase and magnetic inhomogeneity in the samples. These properties would be changed by changing <I>d</I>.</P>

Magneto-transport properties of magnetic tunnelling transistors at low and room temperatures

Quang, H D,Huu, C X,Oh, S K,Dang, V S,Sinh, N H,Yu, S C IOP Pub 2006 Nanotechnology Vol.17 No.14

<P>Si(100)/CoFe/AlO<SUB><I>x</I></SUB><I>/</I>CoFe/FeMn/Cu/Ta magnetic tunnelling transistors (MTTs) with differing base thicknesses (<I>W</I>) were investigated. The magneto-transport properties of the MTTs were measured at 77?K and room temperature (RT). We obtained magneto-current ratios of 48.3% and 55.9% for emitter–base bias voltages of 1.45 and 2.0?V, respectively, at 77?K. The transfer ratios are 2.83 ? 10<SUP>−5</SUP> and 1.52 ? 10<SUP>−4</SUP>, respectively, corresponding to bias voltages of 1.45 and 2.0?V. Moreover, the highest tunnel magneto-resistance (TMR) ratios turned out to be 12% and 20% for a base thickness of 30?Šat RT and 77?K, respectively. These properties raise not only some fundamental questions regarding the phenomenon of spin-independent tunnelling at low and room temperatures, but also show some promising aspect for magneto-electronic applications. In addition, we attempted to elucidate the reason behind the outstanding TMR effect at low and room temperatures. Finally, the origin of the decrease in the mean free path asymmetry (<img SRC='http://ej.iop.org/images/0957-4484/17/14/004/nano218705ieqn1.gif' ALIGN='MIDDLE' ALT='\lambda^{ \uparrow }/\lambda^{\downarrow } '/>) was clarified by using x-ray photoelectron spectroscopy profile analysis of the elements existing in the interface between Si and the CoFe base (Co, Fe, Al, Si, O). </P>

Infrared Spectroscopy, X-ray Diffraction and Neutron Diffraction Study of BaFe$_{\text{12}\bm{-x}}$Al$_{\bm{x}}$O$_\text{19}$ Solid Solutions

R. E. Huseynov,A. I. Mammadov,R. Z. Mehdiyeva,A. V. Trukhanov,S. V. Trukhanov,V. A. Turchenko,T. P. Hoang,N.T. Dang,S. H. Jabarov 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.6

The influences of Al doping on the structural, magnetic and dynamical properties of BaFe$_{12-x}$Al$_x$O$_{19}$ solid solutions ($x = 0.1$--1.2) have been studied by using a combination of X-ray diffraction, neutron diffraction and infrared spectroscopy. The magnetic moment of every Fe atom, including combinations, has been defined, and the magnetic moment of Fe$^{3+}$ ions was found to decrease as the concentration of Al$^{3+}$ diamagnetic ions in the combinations increased. Studies carried out by using infrared spectroscopy showed that four oscillations under normal conditions in these combinations. The results obtained by using infrared spectroscopy for BaFe$_{12-x}$Al$_x$O$_{19}$ combinations were compared with the results obtained by using Raman spectroscopy.

Dielectric properties of nanotube reinforced butyl elastomer composites

Dang, Thi To Nga,Mahapatra, S. P.,Sridhar, V.,Kim, J. K.,Kim, K-J.,Kwak, H. Wiley Subscription Services, Inc., A Wiley Company 2009 Journal of applied polymer science Vol.113 No.3

<P>Dielectric relaxation behavior of multiwalled carbon nanotube reinforced butyl rubber composites has been studied as a function of variation in filler in the frequency range of 20–2 × 106 Hz. The effect of variation in filler loadings on the complex and real parts of impedance was distinctly visible, which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium and relaxation dynamics of polymer chains in the vicinity of fillers. The electric modulus formalism has been used to further investigate the conductivity and relaxation phenomenon. The frequency dependence of AC conductivity has been investigated by using Percolation theory. The phenomenon of percolation in the composites has been discussed based on the measured changes in electric conductivity and morphology of composites at different concentrations of the filler. The percolation threshold as studied by AC conductivity occurred in the vicinity of 6–8 phr of filler loading. Scanning electron microscope microphotographs showed agglomeration of the filler above this concentration and formation of a continuous network structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009</P>