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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.
Ho, T.A.,Dang, N.T.,Phan, T.L.,Yang, D.S.,Lee, B.W.,Yu, S.C. Elsevier Sequoia 2016 Journal of Alloys and Compounds Vol.676 No.-
Polycrystalline orthorhombic samples La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Na<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0-0.09) were prepared by solid-state reaction. The study of magnetic properties revealed that the ferromagnetic-paramagnetic (FM-PM) transition temperature (T<SUB>C</SUB>) increases from 255 to about 271 K with increasing Na-doping content (x) from 0 to 0.09, respectively. Around the T<SUB>C</SUB>, we have found the samples showing a large magnetocaloric (MC) effect with maximum values of magnetic entropy change (|ΔS<SUB>max</SUB>|) of 7-8 J kg<SUP>-1</SUP> K<SUP>-1</SUP> and relative cooling power RCP = 232-236 J/kg for the samples x = 0.03-0.09 in a magnetic-field interval ΔH = 40 kOe. Detailed analyses of isothermal magnetization data M(T, H) based on Banerjee's criteria indicated a first-to-second-order magnetic-phase transformation taking place at a threshold Na-doping concentration x<SUB>c</SUB> ~ 0.06. This could also be observed clearly from the feature of entropy universal curves. An assessment of the magnetic-ordering exponent N = dLn|ΔS<SUB>m</SUB>|/dLnH demonstrates an existence of short-range magnetic order in the samples. We believe that the changes of the magnetic properties and MC effect in La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Na<SUB>x</SUB>MnO<SUB>3</SUB> caused by Na doping are related to the changes in the structural parameters and Mn<SUP>4+</SUP>/Mn<SUP>3+</SUP> ratio, which are confirmed by the geometrical and electronic analyses based on X-ray diffraction and X-ray absorption fine structure.
Magnetic and Magnetocaloric Properties of Zn1−x Co x Fe2O4 Nanoparticles
Phan, T. L.,Tran, N.,Kim, D. H.,Dang, N. T.,Manh, D. H.,Bach, T. N.,Liu, C. L.,Lee, B. W. Springer Science + Business Media 2017 Journal of electronic materials Vol.46 No.7
<P>We have prepared Zn1-x Co (x) Fe2O4 nanoparticles (NPs) by using a hydrothermal method, and then studied their structural and magnetic properties. The analyses of x-ray diffraction (XRD) patterns and Raman scattering spectra reveal that the samples crystallized mainly in a cubic-spinel structure with the lattice parameter a ae 8.4 . Averaged crystallite sizes determined from the XRD linewidth are about 16-22 nm, close to the particle sizes of 19-28 nm determined from scanning electron microscopy images. Magnetization measurements versus temperature, M(T), in the field H = 100 Oe indicate that the ferromagnetic-paramagnetic (FM-PM) phase transition temperature (T (C)) of Zn1-x Co (x) Fe2O4 NPs increases from 606 K for x = 0 to similar to 823 K for x = 1. The features of the M(T) curves also indicate magnetic inhomogeneity in the samples, and their magnetic property is unstable versus temperature. This is ascribed to the changes in the structural characterization and/or concentration of magnetic ions situated at the A and B sites in the spinel lattice. At room temperature, we found that both the saturation magnetization (M (s)) and coercivity (H (c)) increase with increasing Co content, with M (s) = 59-70 emu/g and H (c) = 100-1100 Oe. These results reflect that the Co doping into ZnFe2O4 NPs greatly improves their magnetic property, making them more useful for practical applications. Additionally, we also assess magnetic interactions and the magnetocaloric effect in the samples based on analyzing initial magnetization data, M(H), recorded at temperatures around T (C).</P>
Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds
N.T. Dang,D.P. Kozlenko,Kim Gareoung,손원혁,이종수,Dimitar N. Petrov,T. V. Manh,Phan The Long 한국물리학회 2020 Current Applied Physics Vol.20 No.6
Orthorhombic La0.7-xEuxCa0.3MnO3 samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm3 prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (TC) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around TC reaches the maximum (|ΔSmax|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔSmax| values are about 5.88, 4.93, and 4.71 J/ kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔSmax| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around TC have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La0.7Ca0.3MnO3 materials for magnetic refrigeration below room temperature.
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.
Electronic structure and magnetic properties of BaTi<sub>1-x</sub>Mn<sub>x</sub>O<sub>3</sub>
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>