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Nha Trang, Vietnam

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. Source


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. Source


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. Source


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. Source


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. Source

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