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>

An Effective Route to Control the Magnetic-Phase Transition and Magnetocaloric Effect of La_0.7Ca_0.3MnO₃ Nanoparticles

Phan, T. L.,Thanh, T. D.,Ho, T. A.,Manh, T. V.,Tran, Q. T.,Lampen, P.,Phan, M. H.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11

<P>This paper points out that the magnetic-phase transition and magnetocaloric effect of La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> (LCMO) can be easily controlled by using the mechanical milling method. Changing the milling time from 5 to 30 min, we have obtained LCMO nanoparticles (NPs) with average crystallite sizes (d, determined by the Williamson-Hall method) ranging from 100 to 45 nm. The magnetic studies (based on a superconducting quantum interference device) and simple analyses (based on Banerjee's criteria) prove the magnetic-phase transformation from the first-order to the second-order, which takes place at a threshold value of d located in the range 60-70 nm. Compared with the as-prepared LCMO sample (a first-order magnetic phase transition), though the d decrease reduces the values of the T<SUB>C</SUB>, magnetization, magnetic-entropy change, and refrigerant capacity, but the width of the magnetic phase transition is increased remarkably. This widens the working range of LCMO NPs in magnetic refrigeration applications. We believe that the presence of surface-related effects, lattice strain, and distortions leads to Mn<SUP>3+</SUP>-Mn<SUP>4+</SUP> ferromagnetic interactions in LCMO NPs weaker than that in the as-prepared sample.</P>

Magnetic Properties and Magnetocaloric Effect in Pb-Doped <inline-formula> <tex-math notation='TeX'> <tex> ${\rm La}_{0.9}{\rm Dy}_{0.1}{\rm MnO}_{3}$ </tex> </tex-math></inline-formula> Manganites

Ho, T. A.,Tran Dang Thanh,Thang, P. D.,Jong Suk Lee,Phan, T. L.,Seong Cho Yu IEEE 2014 IEEE transactions on magnetics Vol.50 No.6

<P>We have studied the magnetic properties and magnetocaloric effect of rhombohedral (La<SUB>0.9</SUB>Dy<SUB>0.1</SUB>)<SUB>1-x</SUB>Pb<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0.1, 0.2, and 0.3) fabricated by solid-state reaction. Thermomagnetization curve reveals that the increase of Pb doping in (La<SUB>0.9</SUB>Dy<SUB>0.1</SUB>)<SUB>1-x</SUB>Pb<SUB>x</SUB>MnO<SUB>3</SUB> shifts the ferromagnetic (FM)-paramagnetic (PM) phase-transition temperature (T<SUB>C</SUB>) toward room temperature; the TCvalues determined for x = 0.1, 0.2, and 0.3 are about 172, 249, and 322 K, respectively. Based on magnetic-field dependencies of magnetization, M(H), the magnetic entropy changes (ΔS<SUB>m</SUB>) of the samples were calculated. Under an applied magnetic field of H = 10 kOe, the |ΔS<SUB>max</SUB>| value slightly increases from 0.74 J/kg · K for x = 0.1 to about 1.1 J/kg· K for x = 0.2 and 0.3. These results correspond to a relative cooling power of ~50 J/kg, which is comparable with some perovskite manganites, indicating the applicability of (La<SUB>0.9</SUB>Dy<SUB>0.1</SUB>)<SUB>1-x</SUB>Pb<SUB>x</SUB>MnO<SUB>3</SUB> in magnetic refrigeration devices working around room temperature. Particularly, we find that the variation of |ΔS<SUB>max</SUB>| versus the magnetic field H can be described by a power law |ΔS<SUB>max</SUB>| α Hn, where the magnetic-ordering parameter (n) decreases from 0.861 for x = 0.1-0.834 for x = 0.3. A deviation of the n values estimated from the mean-field theory (n = 2/3) demonstrates an existence of short-range FM order in the samples.</P>

Polarization of amplified spontaneous emission in a plasma active medium

Kim, C. M.,Stiel, H.,Matouš,, B.,Nishikino, M.,Hasegawa, N.,Kawachi, T.,Tran, K. A.,Janulewicz, K. A. American Physical Society 2015 Physical review. A. Atomic, molecular, and optical Vol.92 No.4

A mixture model using Random Rotation Bounding Box to detect table region in document image

Tran, T.A.,Tran, H.T.,Na, I.S.,Lee, G.S.,Yang, H.J.,Kim, S.H. Academic Press 2016 Journal of visual communication and image represen Vol.39 No.-

Table detection in the document image is still a challenging problem due to the variety of table structures and the complexity of document layout. In this paper, we propose a novel method for detecting table regions by using a new shape which is called Random Rotation Bounding Box. This shape is used for illustration and description of the table regions. Based on it, our system performs the following three fundamental steps to detect the table zones: classification of the text and non-text elements in the document image, detection of the ruling-line tables, and identification of the non-ruling-line tables. Different from other methods, our approach can detect most kinds of tables with high precision even when it is skewed. Besides, the proposed method is also designed to fit in the document layout analysis system. Our algorithm has been tested on the two well-known, and a commercial datasets: ICDAR2013 table competition, UNLV, and Diotek. Experimental results on these databases show that our method is more robust and efficient than previous systems.

Critical behavior of Y-doped Nd_0.7Sr_0.3MnO₃ manganites exhibiting the tricritical point and large magnetocaloric effect

Phan, The-Long,Ho, T.A.,Thang, P.D.,Tran, Q.T.,Thanh, T.D.,Phuc, N.X.,Phan, M.H.,Huy, B.T.,Yu, S.C. Elsevier 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.615 No.-

<P><B>Abstract</B></P> <P>We have determined the values of critical exponents of two polycrystalline samples (Nd<SUB>1−</SUB> <I> <SUB>x</SUB> </I>Y<I> <SUB>x</SUB> </I>)<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> (<I>x </I>=0 and 0.07) from the magnetization data versus temperature and magnetic field, <I>M</I>(<I>H</I>, <I>T</I>), to learn about their magnetic and magnetocaloric (MC) properties. The results reveal the samples exhibiting the crossover of first-order and second-order phase transitions, where the exponent values <I>β </I>=0.271 and <I>γ </I>=0.922 for <I>x </I>=0, and <I>β </I>=0.234–0.236 and <I>γ </I>=1.044–1.063 for <I>x </I>=0.07 determined by using modified Arrott plots and static-scaling hypothesis are close to those expected for the tricritical mean-field theory (<I>β </I>=0.25 and <I>γ </I>=1.0). Particularly, the <I>T</I> <SUB>C</SUB> of <I>x </I>=0 and 0.07 can be any value in the temperature ranges of 240–255K and 170–278K, respectively, depending on the magnitude of applied magnetic field and determination techniques. Around the <I>T</I> <SUB>C</SUB>, studying the MC effect of the samples has revealed a large magnetic-entropy change (Δ<I>S</I> <SUB>m</SUB>) up to ∼8J/kgK for the applied field interval Δ<I>H </I>=50kOe, corresponding to refrigerant capacity values of 200–245J/kg. These phenomena are related to the crossover nature and the persisting of FM/anti-FM interactions even above the <I>T</I> <SUB>C</SUB>, as further confirmed by electron-spin-resonance data, Curie–Weiss law-based analyses, and an exponential parameter characteristic of magnetic order <I>n </I>=dLn|Δ<I>S</I> <SUB>m</SUB>|/dLn<I>H</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Tricritical point in Y-doped Nd<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> manganites. </LI> <LI> A large magnetic-entropy change. </LI> <LI> Magnetic inhomogeneity and phase separation. </LI> </UL> </P>

A Classification and Regression Trees (CART) Model of Parallel Structure and Long-term Prediction Prognosis of Machine Condition

Tran, V.T.,Yang, B.-S.,Tan, A.C.C. SAGE PUBLICATIONS 2010 Structural health monitoring Vol.9 No.2

Electronic structure and magnetic properties of BaTi_1-xMn_xO₃

Dang, N.V.,Dang, N.T.,Ho, T.A.,Tran, N.,Phan, T.L. Elsevier 2018 CURRENT APPLIED PHYSICS Vol.18 No.2

<P>The electronic structure and magnetic properties of polycrystalline BaTi1-xMnxO3 (x = 0-0.1) compounds prepared by solid-state reactions were studied. The results revealed that the increase in Mn content (x) did not change the oxidation numbers of Ba (+2) and Ti (+4) in BaTi1-xMnxO3. However, there is the change in Mn valence that Mn-3+,Mn-4+ ions coexist in the samples with x = 0.01-0.04 while Mn4+ ions are almost dominant in the samples with x = 0.06-0.1. We also point out that Mn3+ and Mn4+ ions substitute for Ti4+ and prefer locating in the tetragonal and hexagonal BaTiO3 structures, respectively, in which the hexagonal phase constitutes soon as x = 0.01. Particularly, all the samples exhibit room-temperature ferromagnetism. Ferromagnetic order increases with increasing x from 0 to 0.02, but decreases as x >= 0.04. We think that ferromagnetism in BaTi1-xMnxO3 is related to lattice defects and/or exchange interactions between Mn3+ and Mn4+ ions. (C) 2017 Elsevier B.V. All rights reserved.</P>

Electronic structure and magnetic properties of BaTi1-xMnxO3

N.V. Dang,N.T. Dang,T.A. Ho,N. Tran,T. L. Phan 한국물리학회 2018 Current Applied Physics Vol.18 No.2

The electronic structure and magnetic properties of polycrystalline BaTi1-xMnxO3 (x ¼ 0e0.1) compounds prepared by solid-state reactions were studied. The results revealed that the increase in Mn content (x) did not change the oxidation numbers of Ba (þ2) and Ti (þ4) in BaTi1-xMnxO3. However, there is the change in Mn valence that Mn3þ,4þ ions coexist in the samples with x ¼ 0.01e0.04 while Mn4þ ions are almost dominant in the samples with x ¼ 0.06e0.1. We also point out that Mn3þ and Mn4þ ions substitute for Ti4þ and prefer locating in the tetragonal and hexagonal BaTiO3 structures, respectively, in which the hexagonal phase constitutes soon as x ¼ 0.01. Particularly, all the samples exhibit roomtemperature ferromagnetism. Ferromagnetic order increases with increasing x from 0 to 0.02, but decreases as x 0.04. We think that ferromagnetism in BaTi1-xMnxO3 is related to lattice defects and/or exchange interactions between Mn3þ and Mn4þ ions.

A robust system for document layout analysis using multilevel homogeneity structure

Tran, T.A.,Oh, K.,Na, I.S.,Lee, G.S.,Yang, H.J.,Kim, S.H. Pergamon ; Elsevier Science Ltd 2017 expert systems with applications Vol.85 No.-

One of the difficulties in the understanding of document images is document layout analysis, which is the first step in document image modeling. In this paper, a robust system for which a multilevel-homogeneity structure is used in accordance with a hybrid methodology is proposed to deal with this problem. Our system consists of the following three main stages: classification, segmentation, and refinement and labeling. Different from other page segmentation methods, the proposed system includes an efficient algorithm to detect table regions in document images. Besides, to create an effective application, the proposed system is designed to work with a variety of document languages. The proposed method was tested with the ICDAR2015 competition (RDCL-2015) and three other published datasets in different languages. The results of these tests show that the accuracy of proposed system is superior to the previous methods.