Nha Trang Pedagogic College

Nha Trang, Vietnam

Nha Trang Pedagogic College

Nha Trang, Vietnam
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Phong P.T.,Nha Trang Pedagogic College | Bau L.V.,Hong Duc University | Hoan L.C.,Nha Trang Pedagogic College | Manh D.H.,Vietnam Academy of Science and Technology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2015

Magnetic, magnetocaloric and electro-transport properties of La0.7Sr0.3Mn1-xAlxO3 compounds in the composition range 0 ≤ x ≤ 0.2 were investigated. For x ≥ 0.15 composition, it shows that the compounds with higher Al concentration show Griffiths phase-like behavior above the Curie temperature. The observed anomalous paramagnetic behavior is attributed to the existence of ferromagnetic clusters in the paramagnetic domain. Both the experimental and theoretical approaches were adopted to calculate the magnetocaloric behavior of Al-doped La0.7Sr0.3MnO3. The important parameters such as maximum entropy change, full width at half maximum, relative cooling power, and maximum adiabatic temperature have been explained qualitatively. Moreover, to understand the electrical transport properties of x ≥ 0.1 samples, we applied phase-coexistence transport model, which depends on the coexistence and competition of ferromagnetic metallic phases and paramagnetic insulating phases. This model is in perfect agreement with experimental results over the whole range of temperatures studied. © 2015 Elsevier B.V. All rights reserved.


Thanh T.D.,Chungbuk National University | Thanh T.D.,Institute of Materials Science | Manh D.H.,Institute of Materials Science | Phan T.L.,Chungbuk National University | And 4 more authors.
Journal of Applied Physics | Year: 2014

We have studied the magnetic and spin-glass (SG) properties of La 0.7Ca0.3MnO3 single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (tm). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (Tf) appearing on the real part curve of the ac susceptibility, χ′(T). The Tf value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c= ΔTf/T fΔ(log10f), and the power law τ= τ0(T/Tg - 1)-zν. The obtained values of c ≈5×10-2, τ0 ≈ 10-5 s and zν ≈ 2-3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at T g below Tf, which decreases with decreasing 〈D〉. Basing on ln(f) versus Tf data, and the Néel-Arrhenius model [ln(f)=ln(f0) - Ea/kBT] and Vogel-Fulcher law [ln(f)=ln(f0) - Ea/kB(T - T0)], the Larmor frequency (f0), activation energy (Ea) and effective temperature (T0) for the samples with different 〈D〉 were determined. Obtained results indicate the existence a strong interaction between nanoparticles. © 2014 AIP Publishing LLC.


Manh D.H.,Vietnam Academy of Science and Technology | Thanh T.D.,Vietnam Academy of Science and Technology | Phuc N.X.,Vietnam Academy of Science and Technology | Hong L.V.,Vietnam Academy of Science and Technology | And 2 more authors.
International Journal of Nanotechnology | Year: 2011

Reactive milling and thermal processing methods were used to prepare a large variety of perovskites like ABO3 and La2NiO 4. The single-phase nanoparticle of ABO3 was synthesised at different milling times in dependence on the starting oxides. The grain size of ABO3 nanoparticles in the range of 10-30 nm was conditional upon milling time. Single-phase nanoparticles of La2NiO4 were obtained by using 6 h milling combined with annealing at 750°C. A structure conversion from a layer into a single perovskite of La2NiO 4 was observed as milling time increased, whereas the crystalline structure of ABO3 remained almost unchanged. Further analysis of HRTEM images confirms a core-shell structure of nanoparticles. Copyright © 2011 Inderscience Enterprises Ltd.


Phong P.T.,Dongguk University | Phong P.T.,Nha Trang Pedagogic College | Manh D.H.,Vietnam Academy of Science and Technology | Dang N.V.,Thai Nguyen University | And 2 more authors.
Physica B: Condensed Matter | Year: 2012

We report the structural, magentoresistance and electro-magnetic properties of ferromagnet-ferroelectric-type (1-x)La 0.7Sr 0.3MnO 3/xBaTiO 3 (with x=0.0%, 3.0%, 6.0%, 12%, 15.0% and 18.0%, in wt%) composites fabricated through a solid-state reaction method combined with a high energy milling method. The insulator-metal transition temperature shifts to a lower temperature and resistivity increases while the feromagnetic-paramagnetic transition temperature remains almost unchanged with the increase of BaTiO 3 content. Magnetoresistance of the composites at an applied magnetic field H=3 kOe is enhanced in the wide temperature ranges with the introduction of BaTiO 3, which could be explained by the enhanced spin polarized tunneling effect induced by the introduction of BaTiO 3. The low-field magnetoresistance of the composite is analyzed in the light of a phenomenological model based on the spin polarized tunneling at the grain boundaries. Furthermore, the temperature dependence of resistivity for this series has been best-fitted by using the adiabatic small polaron and variable range hopping models. These models may be used to explain effect of BTO on the electronic transport properties on high temperature paramagnetic insulating region. © 2012 Elsevier B.V. All rights reserved.


Thanh T.D.,Vietnam Academy of Science and Technology | Nguyen L.H.,Nha Trang Pedagogic College | Manh D.H.,Vietnam Academy of Science and Technology | Chien N.V.,Vietnam Academy of Science and Technology | And 4 more authors.
Physica B: Condensed Matter | Year: 2012

A systematic investigation of the structural, magnetic and electrical properties of a series of nanocrystalline La0.7SrxCa 0.3-xMnO3 materials, prepared by high energy ball milling method and then annealed at 900 °C has been undertaken. The analysis of the XRD data using the Win-metric software shows an increase in the unit cell volume with increasing Sr ion concentration. The La0.7SrxCa 0.3-xMnO3 compounds undergo a structural orthorhombic-to-monoclinic transition at x=0.15. Electric and magnetic measurements show that both the Curie temperature and the insulator-to-metal transition temperature increase from 259 K and 253 K correspondingly for La 0.7Ca0.3MnO3 (x=0) to 353 K and 282 K, respectively, for La0.7Sr0.3MnO3 (x=0.3). It is argued that the larger radius of Sr2 ion than that of Ca2 is the reason to strengthen the double-exchange interaction and to give rise to the observed increase of transition temperatures. Using the phenomenological equation for conductivity under a percolation approach, which depends on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, we fitted the resistivity versus temperature data measured in the range of 50320 K and found that the activation barrier decreased with the raising Sr2 ion concentration. © 2011 Elsevier B.V. All rights reserved.


Thanh T.D.,Vietnam Academy of Science and Technology | Linh D.C.,Vietnam Academy of Science and Technology | Uyen Tuyen N.T.,Nha Trang Pedagogic College | Phan T.-L.,Hankuk University of foreign Studies | Yu S.-C.,Chungbuk National University
Journal of Alloys and Compounds | Year: 2015

La0.7Ca0.3-xBaxMnO3 nanoparticles with the crystalline size d = 38 and 39 nm for x = 0.025, and 0.05, respectively, were synthesized by utilizing the solid-state reaction and mechanical ball milling methods. We have used the Banerjee's criteria, the mean-field, and the thermodynamic theories, and isothermal magnetization, M(H), data around Curie temperature (TC) to investigate the magnetic phase transformation and the temperature (T) and magnetic field (H) dependences of magnetic entropy change, ΔSm(T, H), for nanoparticles. These exhibit the samples undergoing a second-order magnetic phase transition with an existence of the short-range ferromagnetic order in the samples. Under an applied magnetic field change ΔH = 30 kOe, the maximum value of ΔSm (denoted as |ΔSmax|) are obtained about 4.4 J kg-1 K-1 corresponding to a relative cooling power (RCP) value about 140 J kg-1. Field dependences of |ΔSmax| and RCP can be expressed by the power laws, |ΔSmax| = a × Hn and RCP = b × HN, where a and b are coefficients, n and N are the field exponents, respectively. Interestingly, all the ΔSm(T, H) curves measured at different applied fields are collapsed onto a universal curve, ΔSm(T, H)/ΔSmax versus θ = (T - TC)/(Tr - TC), where Tr is the reference temperature. © 2015 Elsevier B.V.


Thanh T.D.,Chungbuk National University | Thanh T.D.,Vietnam Academy of Science and Technology | Phong P.T.,Nha Trang Pedagogic College | Manh D.H.,Vietnam Academy of Science and Technology | And 4 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2013

A manganite composite series of (1 - x)La0.7Sr 0.3MnO3/xBaTiO3 (x = 0, 0.06, 0.12, and 0.18) has been fabricated by solid-state reaction combined with a high-energy mechanical milling method. Experimental results revealed that the insulator-metal transition temperature was shifted towards lower temperatures, and resistivity increases with increasing BaTiO3 content in (1 - x)La0.7Sr0.3MnO3/xBaTiO3. Meanwhile, the ferromagnetic-paramagnetic transition temperature was almost unchanged. The increase in magnetoresistance was observed in the all composites at whole measurement temperatures under an applied magnetic field of 3 kOe. Here, temperature dependences of magnetoresistance display a Curie-Weiss law-like behavior. The nature of this phenomenon is explained in detail. © 2012 Springer Science+Business Media New York.


Manh D.H.,Vietnam Academy of Science and Technology | Phong P.T.,Nha Trang Pedagogic College | Thanh T.D.,Vietnam Academy of Science and Technology | Nam D.N.H.,Vietnam Academy of Science and Technology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

La0.7Ca0.3MnO3 (LCMO) nanoparticles with average diameter of 16-73 nm were prepared by reactive milling and thermal processing methods. Interaction and size effects on the magnetic properties of the LCMO nanoparticle samples were investigated. Phenomena related to the interparticle interaction, such as an un-overlapping of the M(H ext,T)/MS vs. Hext/T scaling plots and a Curie-Weiss rather than Curie law behavior of the dc susceptibility at high temperatures were analyzed. The magnetization curves of interacting nanoparticles were well described by using the mean-field approximation. The dependence of the blocking temperature TB on the strength of the interactions, magnetic anisotropy, as well as the thermal dependence of magnetization deviates from the expected Bloch law was also estimated. © 2010 Elsevier B.V. All rights reserved.


Manh D.H.,Vietnam Academy of Science and Technology | Phong P.T.,Nha Trang Pedagogic College | Thanh T.D.,Vietnam Academy of Science and Technology | Hong L.V.,Vietnam Academy of Science and Technology | Phuc N.X.,Vietnam Academy of Science and Technology
Journal of Alloys and Compounds | Year: 2010

Nanocrystalline, granular samples of La0.7Ca0.3MnO3 (LCMO) were synthesized by reactive milling method and annealed at various temperatures. Effect of grain size on the low-field magnetoresistance (LFMR) has been investigated. Based upon a phenomenological model taking into account the spin-polarized transport across grain boundaries, we explained magnetic field dependence of magnetoresistance in LCMO samples. The contribution to the magnetoresistance coming from spin-polarized tunneling was separated out from the intergranular contribution. The fitted results showed that the temperature dependence of the LFMR displays a Curie-Weiss law-like behavior. © 2010 Elsevier B.V. All rights reserved.


Manh D.H.,Vietnam Academy of Science and Technology | Phong P.T.,Nha Trang Pedagogic College | Thanh T.D.,Vietnam Academy of Science and Technology | Hong L.V.,Vietnam Academy of Science and Technology | Phuc N.X.,Vietnam Academy of Science and Technology
Journal of Alloys and Compounds | Year: 2010

Nanocrystalline samples of La0.7Ca0.3MnO3 were synthesized by reactive milling method and annealed at various temperatures. Effect of particle size on the magnetic and electrical properties was investigated. While the ferromagnetic-paramagnetic transition temperature TC does not show significant change, metal-insulator TMI is markedly affected by particle size. Experimental data indicates linear relationship of magnetization and resistivity to the surface/volume ratio of the particles with different mean sizes. A phenomenological model, describing competition between the FM and PI phases used to elucidate temperature dependence of the resistivity with and without magnetic field, agrees quantitatively with experimental observations. © 2009 Elsevier B.V. All rights reserved.

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