Optical Spectra of the Colloidal Fe-doped Manganate CaMn1−xFexO3 (x = 0, 0.01, 0.03, 0.05)

Duc Huyen Yen Pham,Duc Tho Nguyen,Duc Thang Pham,Nam Nhat Hoang,The Tan Pham 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12

We report the optical behaviors of the Fe-doped CaMnO3 family of compounds at low dopingconcentrations x 5%. The study aims at assisting the evaluation of the competition between ferroandantiferromagnetic orderings, which is believed to be a cause of many interesting properties of thisclass of compounds, including the magnetization reversal effect recently discovered. The structuralcharacterization showed a predominant orthorhombic phase with slightly increased cell constantsdue to doping. The Raman spectra revealed changes associated with the Mn sites, and the IRabsorption spectrum showed a characteristic Fe band at 1.2 eV, which should be accompanied bya change of spin. The analysis of the magnetization data allowed us to predict that while thedoping reduced the ferromagnetic coupling strength, and therefore the TC, the maximal dopingconcentration for the effective exchange to be zero was around 14%.

Critical Behavior in La_0.75Ca_0.2Ag_0.05MnO₃ Exhibiting the Griffiths Phase

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>

Magnetic and magnetocaloric properties in second-order phase transition La_1−xK_xMnO₃ and their composites

Thanh, Tran Dang,Linh, Dinh Chi,Yen, Pham Duc Huyen,Bau, Le Viet,Ky, Vu Hong,Wang, Zhihao,Piao, Hong-Guang,An, Nguyen Manh,Yu, Seong-Cho Elsevier 2018 PHYSICA B-CONDENSED MATTER - Vol.532 No.-

<P><B>Abstract</B></P> <P>In this work, we present a detailed study on the magnetic properties and the magnetocaloric effect (MCE) of La<SUB>1−x</SUB>K<SUB>x</SUB>MnO<SUB>3</SUB> compounds with <I>x</I>=0.05–0.2. Our results pointed out that the Curie temperature (<I>T</I> <SUB>C</SUB>) could be controlled easily from 213 to 306K by increasing K-doping concentration (<I>x</I>) from 0.05 to 0.2. In the paramagnetic region, the inverse of the susceptibility can be analyzed by using the Curie-Weiss law, <I>χ</I>(<I>T</I>)=<I>C</I>/(<I>T</I>−<I>θ</I>). The results have proved an existence of ferromagnetic clusters at temperatures above <I>T</I> <SUB>C</SUB>. Based on Banerjee's criteria, we also pointed out that the samples are the second-order phase transition materials. Their magnetic entropy change was calculated by using the Maxwell relation and a phenomenological model. Interestingly, the samples with <I>x</I>=0.1–0.2 exhibit a large MCE in a range of 282–306K, which are suitable for room-temperature magnetic refrigeration applications. The composites obtained from single phase samples (<I>x</I>=0.1–0.2) exhibit the high relative cooling power values in a wide temperature range. From the viewpoint of the refrigerant capacity, the composites formed out of La<SUB>1−x</SUB>K<SUB>x</SUB>MnO<SUB>3</SUB> will become more useful for magnetic refrigeration applications around room-temperature.</P>

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>

Determinant factors impact on participation intention in Smart Classroom environment

Do-Van-Anh Tran,Dinh-Bao-Nhi Le,Huyen-Yen-Nhi Vo,Hoanh-Su Le 한국경영정보학회 2022 한국경영정보학회 학술대회논문집 Vol.2022 No.6

Factors Affecting Parents' Intention to Choose English Centers: The Role of STEM Education

Tran, Do-Van-Anh,Nguyen, Ngoc-Duyen,Tang, Thai-Ngoc,Le, Dinh-Bao-Nhi,Vo, Huyen-Yen-Nhi,Le, Hoanh-Su Korea Multimedia Society 2020 The journal of multimedia information system Vol.7 No.1

Parents' desire for daily English practice for students and the urge for a etter English education has led to a demand for a highly qualified educational curriculum. In addition to getting deep-dive insights into parents' decision-making process, the increasingly important role of STEM education method has been proved in accordance with plenty of evidenced-based many of previous research. This study was conducted to examine the five independent factors affecting parents' intentions when designating English centers for their children, respectively named: Facility, Teachers, Brands, Social factors and Tuition. Through a preliminary approach, 235 samples were analyzed. Analysis of the sample responses reveals the importance level of five independent factors affecting Parents' intention to choose English centers in descending order: Facilities, Teachers, Brands, Tuition and Social factors. Furthermore, a positive correlation was found between STEM and Intention to choose English centers, indicating that whether the center applies STEM-related curriculum in English courses or not, in fact, has a significant impact on parents' decision. In terms of attitude towards STEM, further statistical tests revealed an interesting finding, which is the fact that how STEM affects Intention of parents is directly proportional to the Attitude towards STEM. With the help of SPSS 20 and AMOS 20, the SEM analysis was processed in order to draw conclusions about factors impacting Intentions to choose English centers. Combining with Multi-group analysis, the major role of STEM education has been assessed in relation to plenty of correlations. In light of recent major and massive growth of English teaching market in Vietnam, several suggestions and recommendations in terms of sustainable developments have been displayed in this research.