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Ho, T. A.,Phan, T. L.,Thang, P. D.,Yu, S. C. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.5
<P>We used the modified Arrott plot method to analyze the magnetic field dependence of the magnetization, M(H), for a perovskite-type manganite (La0.9Dy0.1)(0.8)Pb0.2MnO3, and determined the critical parameter values T (C) = 248.4 K, beta = 0.484 +/- A 0.002, gamma = 0.961 +/- A 0.012, and delta = 2.90 +/- A 0.01. With these exponent values, the M(H) data around T (C) fall on two universal branches of a scaling function M(H,epsilon) = |epsilon| (beta) f (+/-)(H/|epsilon| (beta + gamma) ), where epsilon = (T - T (C))/T (C) is the reduced temperature, f (+) for T > T (C) and f (-) for T < T (C). Comparing with theoretical models, the exponent values obtained in our work are quite close to those expected from mean-field theory (with beta = 0.5, gamma = 1, and delta = 3). This reveals nearly long-range ferromagnetic order existing in (La0.9Dy0.1)(0.8) Pb0.2MnO3. From the M(H) data, we also found that, around the ferromagnetic-paramagnetic phase-transition temperature (T (C)), the magnetic entropy change reaches a maximum value (|delta S (max)|) of about 1.1 J kg(-1) K-1 for H = 10 kOe, corresponding to relative cooling power (RCP) of 50 J/kg. In addition to the above investigation, the temperature dependence of the magnetization, remanent magnetization (M (r)), and coercivity (H (c)) were recorded to learn about the physical processes taking place in (La0.9Dy0.1)(0.8)Pb0.2MnO3.</P>
Ho, T. A.,Phan, M. H.,Phuc, N. X.,Lam, V. D.,Phan, T. L.,Yu, S. C. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.5
<P>The Ti-substitution influence on the magnetic and magnetocaloric properties of La0.7Ba0.3Mn1-x Ti (x) O-3 (x = 0.05 and 0.1) was investigated. Based on Banerjee's criteria and Franco's universal curves, we proved the existence of a second-order magnetic phase transition in the samples. Using the modified Arrott plot method, we determined the critical parameters T (C) a parts per thousand 245 K, beta = 0.374 +/- A 0.013, gamma = 1.228 +/- A 0.045, and delta = 4.26 +/- A 0.03 for x = 0.05, and T (C) a parts per thousand 169 K, beta = 0.339 +/- A 0.001, gamma = 1.307 +/- A 0.003, and delta = 4.78 +/- A 0.02 for x = 0.1. With these critical values, the predictable scaling behavior of the M(H) data above and below T (C) proves that the calculated exponents are unambiguous and intrinsic. The values beta = 0.374 for x = 0.05 and beta = 0.339 for x = 0.1 suggest that the magnetic phase transition of the samples falls into the three-dimensional (3D) Heisenberg and 3D Ising universality classes, respectively, corresponding to short-range ferromagnetic (FM) order due to FM clusters in a wide temperature range even above T (C), as confirmed by electron spin resonance studies. In reference to the magnetocaloric effect around T (C), the magnetic entropy change reaches maximum values (|Delta S-max|) of about 4 and 3 J kg(-1) K-1 for x = 0.05 and 0.1, respectively, for a magnetic field change 50 kOe. Magnetic field dependencies of |Delta S-max| obey a power function |Delta S-max(H)| ae H (n) , where exponent values n = 0.59 and 0.61 for x = 0.05 and 0.1, respectively, were determined from the relation n = 1 + (beta-1)/(beta + gamma). The difference between the experimental n values and the theoretical value n = 2/3 of the mean field model is due to the presence of short-range FM order in the samples.</P>
Ho, T.A.,Lim, S.H.,Tho, P.T.,Phan, T.L.,Yu, S.C. Elsevier 2017 Journal of magnetism and magnetic materials Vol.426 No.-
<P><B>Abstract</B></P> <P>The magnetic Mn<SUP>3+</SUP> ions in La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> are partially replaced by nonmagnetic Zn<SUP>2+</SUP> ions to form La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>Mn<SUB>1−x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> compounds (<I>x</I>=0.0, 0.06, 0.08, and 0.1), and their magnetic and magnetocaloric properties are investigated. The Curie temperature decreases drastically from 245 to 70K as <I>x</I> increases from 0 to 0.1. An analysis using the Banerjee's criterion of the experimental results for magnetization as a function of temperature and magnetic field indicates that the first-to-second order magnetic phase transformation occurs at a threshold composition of <I>x</I>=0.06, which is further supported by the universal curves of the normalized entropy change versus reduced temperature. The maximum magnetic entropy change measured at a magnetic field span of 50kOe, which occurs near the Curie temperature, decreases from 10.30 to 2.15J/kgK with the increase of <I>x</I> from 0.0 to 0.1. However, the relative cooling power, an important parameter for practical applications, shows a maximum value of 404J/kg at <I>x</I>=0.08, which is 1.5 times greater than that observed for the undoped sample.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic and MCE of La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>Mn<SUB>1−x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> are investigated. </LI> <LI> Order of magnetic phase transition is dependent on the Zn doping concentration. </LI> <LI> Although the |∆<I>S</I> <SUB>max</SUB>| decreases with increasing <I>x</I>, <I>RCP</I> increase remarkably. </LI> </UL> </P>
Ho, T.A.,Lim, S.H.,Phan, T.L.,Yu, S.C. Elsevier 2017 Journal of alloys and compounds Vol.692 No.-
<P><B>Abstract</B></P> <P>The magnetic properties of La<SUB>0.7-<I>x</I> </SUB>Pr<SUB> <I>x</I> </SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> (<I>x</I> = 0.0, 0.2, 0.3, 0.4, and 0.5) compounds fabricated by a solid-state reaction are studied by using Arrott plots and universal curves. The Arrott plots near the Curie temperature show negative slopes over the entire magnetic field range up to 50 kOe, indicating a first-order magnetic phase transition (according to Banerjee's criterion) for the <I>x</I> = 0.0, 0.2, 0.3, and 0.4 samples. For the <I>x</I> = 0.5 sample, however, the plots show positive slopes at low magnetic fields below 10 kOe, indicating a second-order transition. These results are further checked by universal curves of the normalized entropy change versus reduced temperature. The universal curves show a divergence among the curves with different magnetic fields for a first-order magnetic transition, but for a second-order transition, they collapse onto the same curve. The Curie temperature, around which the maximum magnetic entropy change occurs, decreases continuously from 260 to 110 K as <I>x</I> increases from 0.0 to 0.5. In the same <I>x</I> range, the maximum entropy change measured at a magnetic field span of 50 kOe decreases from 10.70 to 7.14 J/kg K, but the relative cooling power increases from 278 to 380 J/kg under the same magnetic field span.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic and magnetocaloric properties of manganites are investigated. </LI> <LI> Universal curves are used to assess the magnetic transition order of manganites. </LI> <LI> Pr is substituted for La in LCMO to optimize the magnetocaloric properties. </LI> </UL> </P>
Ho, T.A.,Lim, S.H.,Kim, C.M.,Jung, M.H.,Ho, T.O.,Tho, P.T.,Phan, T.L.,Yu, S.C. Elsevier 2017 Journal of magnetism and magnetic materials Vol.438 No.-
<P><B>Abstract</B></P> <P>La<SUB>0.6</SUB>Ca<SUB>0.4−</SUB> <I> <SUB>x</SUB> </I>Ce<I> <SUB>x</SUB> </I>MnO<SUB>3</SUB> (<I>x</I> =0, 0.03, 0.06, and 0.09) compounds are fabricated by a solid-state reaction, and their structural, magnetic, and magnetocaloric properties are investigated. The Curie temperature at which a ferromagnetic–paramagnetic transition occurs decreases from 260 to 221K as <I>x</I> increases from 0 to 0.09. The saturation magnetization also decreases with the increase of <I>x</I>. The experimental results for the magnetization with respect to the temperature and magnetic field are analyzed using the Banerjee criterion, revealing that all the samples undergo the second-order magnetic phase transition. The maximum magnetic entropy change measured at a magnetic-field span of 50kOe, which occurs near the Curie temperature, slightly increases from 6.31 to 7.62J/kg K as <I>x</I> increases from 0 to 0.09.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic and MCE of La<SUB>0.6</SUB>Ca<SUB>0.4−x</SUB>Ce<SUB>x</SUB>MnO<SUB>3</SUB> are investigated. </LI> <LI> All the samples underwent the second-order magnetic transition. </LI> <LI> Ce dopant favored the enhancement of the MCE. </LI> </UL> </P>
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>