Influence of Pr-doping on the magnetic properties and magnetocaloric effect of Ni_50-xPr_xMn₃₇Sn₁₃ alloys

Phan, T.L.,Thanh, P.T.,Dan, N.H.,Zhang, P.,Thanh, T.D.,Phan, M.H.,Yu, S.C. Elsevier Sequoia 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.615 No.suppl1

We have studied the magnetic and magnetocaloric (MC) properties of Ni<SUB>50-x</SUB>Pr<SUB>x</SUB>Mn<SUB>37</SUB>Sn<SUB>13</SUB> (x=0, 1, 3, and 5) alloy ingots fabricated by arc-melting. Experimental results revealed a coexistence of the conventional and inverse MC effects in the samples with x=0, 1, and 3. There is a gradual decrease of the magnetization and magnetic-entropy change (ΔS<SUB>m</SUB>) when Pr-doping content increases. However, the Curie temperature of the austenitic phase (T<SUB>C</SUB><SUP>A</SUP>) around room temperature was not changed very much. Particularly, doping a small amount of Pr with x=1 enhances remarkably the linewidth of the peaks in its ΔS<SUB>m</SUB>(T) curves. This increases the relative cooling power (RCP) of Ni<SUB>50-x</SUB>Pr<SUB>x</SUB>Mn<SUB>37</SUB>Sn<SUB>13</SUB> alloys when they are used as coolants in refrigeration devices. For example, under an applied field of H=50 kOe, the RCP increases from 150 for x=0 to ~200J/kg for x=1. Higher Pr contents reduce quickly the MC effect because of the formation of nonmagnetic secondary phases.

Electron Spin Resonance Spectra of <tex> ${\hbox{La}}_{0.7}{\hbox{Cd}}_{0.3}({\hbox{Mn}},{\hbox{Co}}){\hbox{O}}_{3}$</tex> Perovskites

Phan, T. L.,Thanh, T. D.,Phan, M. H.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.1

<P>We have prepared two perovskite samples La<SUB>0.7</SUB>Cd<SUB>0.3</SUB>MnO<SUB>3</SUB> (LCMO) and La<SUB>0.7</SUB>Cd<SUB>0.3</SUB>CoO<SUB>3</SUB> (LCCO) by using a solid-state reaction technique and studied their electron spin resonance (ESR) spectra versus temperature up to ~500 K. Experimental results reveal that as compared to LCMO, the resonant signals of LCCO are weaker and easily extinguished by thermal energy. For both samples, there exists a temperature called T<SUB>min</SUB> at which the narrowest ESR linewidth (ΔH) is obtained. At temperatures , the resonant lines associated with the ferromagnetic phase are asymmetrical. They become a symmetrical single line in the Lorentzian shape when the samples enter the paramagnetic region with T > T<SUB>min</SUB>. A detailed analysis of resonant spectra in this paramagnetic region reveals that temperature dependences of ΔH can be described by a linear function of the single-phonon process. The resonant intensity versus temperature obeys an exponent function I = I<SUB>0</SUB> exp(E<SUB>a</SUB>/k<SUB>B</SUB>T), where E<SUB>a</SUB> is the activation energy associated with decomposition of ferromagnetic clusters. Temperature dependences of the resonant position (H<SUB>r</SUB>) and the Lande factor (g) indicate the dominance of spin-spin and spin-lattice interactions in both LCMO and LCCO, but with the additional presence of the spin-orbit interaction in LCCO at high temperatures (T > 380 K). We believe that the differences in the electronic structure of e<SUB>g</SUB> and t<SUB>g</SUB> levels, as well as in the electronic spin configuration of Mn and Co ions, caused the distinct difference in the ESR spectra of LCMO and LCCO.</P>

Ultrasoft magnetic properties of Co–Fe–Hf–O nanocomposite films

Ha, N. D.,Phan, M. H.,Tuan, L. A.,Phan, T. L.,Kim, C. G.,Kim, C. O.,Yu, S. C. WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12

<P>This paper reports on the excellent high-frequency magnetic performance of Co–Fe–Hf–O thin films, which were deposited on Si(100) substrates by the oxygen reactive rf-sputtering method. It was shown that the films possessed not only high electrical resistivity but also large saturation magnetization and hard-axis anisotropy field. Among the compositions investigated, Co<SUB>19.35</SUB>Fe<SUB>53.28</SUB>Hf<SUB>7.92</SUB>O<SUB>19.35</SUB> exhibited the ultrasoft magnetic properties of high saturation magnetization, 4πM<SUB>s</SUB> ∼19.86 kG, and low coercivity, H<SUB>c</SUB> ∼1.5 Oe. The magnetic permeability remained almost constant up to 3 GHz and reached a maximum at the ferromagnetic resonant frequency of 4.024 GHz. These properties of this film together with a high electrical resistivity of 3569 μΩcm make it ideal for producing micromagnetic devices for high-frequency applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Magnetic properties and magnetocaloric effect in Fe90-x Sn x Zr10 alloy ribbons

Phan, T. L.,Dan, N. H.,Thanh, T. D.,Mai, N. T.,Ho, T. A.,Yu, S. C.,Le, Anh-Tuan,Phan, M. H. Korean Physical Society 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.8

<P>This work points out the possibility of tuning the magnetocaloric (MC) effect in Fe90-x Sn (x) Zr-10 alloy ribbons in the temperature range from 235 to 315 K by changing the Sn-doping content (x). Under an applied field change from 0 to 50 kOe, the maximum magnetic-entropy changes around the ferromagnetic-paramagnetic phase transition are about 3.6, 4.1 and 3.3 J kg(-1)center dot K-1 for x = 0, 2 and 4, respectively, which correspond to relative cooling powers of 280 similar to 410 J center dot kg(-1). Studying the magnetic properties of the alloy ribbons based on Banerjee's criteria and assessing the magneticordering parameter n = dLn|Delta S (m) |/dLnH (where Delta S (m) and H are the magnetic-entropy change and the magnetic field, respectively) reveals that the alloys undergo a second-order phase transition and exhibit a short-range ferromagnetic order. The nature of these phenomena is further analyzed by means of the results obtained from the analyses of the crystal structure, the Curie-Weiss law, and the Griffith phase.</P>

Influence of film thickness on the electrical and magnetic properties of Co–Fe–Al–O films

Phan, M. H.,Tuan, L. A.,Ha, N. D.,Phan, T. L.,Kim, C. G.,Kim, C. O.,Yu, S. C. WILEY-VCH Verlag 2007 Physica Status Solidi C Vol.4 No.12

<P>Influence of film thickness (t) on the electrical and magnetic properties of Co–Fe–Al–O films has been systematically investigated via means of vibrating sample magnetometry (VSM), permeability spectra and magneto-optical Kerr effect (MOKE). It is found that the electrical resistivity (ρ) decreases as the film thickness increases; ρ = 412.5 µΩcm for the t = 600 nm sample decreases to ρ = 368.2 µΩcm for the t = 1200 nm sample. The coercive force, measured along the easy-axis direction, decreases as the film thickness increases. Interestingly, along the hard-axis magnetization direction, the magnetic hysteresis loop is reversed and the coercive force is negative for the t = 600 and 800 nm samples. However, this peculiar feature disappears as t reaches 1200 nm, which is probably attributed to the microstructural change with respect to changes of film thickness. At a frequency of 1GHz, the hard-axis effective permeability decreases from 1252 to 1000 as the film thickness increases from 600 to 1200 nm, respectively. The VSM and MOKE results reveal an increase in magnetic anisotropy in the near-surface region of the film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Critical behavior of Y-doped Nd_0.7Sr_0.3MnO₃ manganites exhibiting the tricritical point and large magnetocaloric effect

Phan, The-Long,Ho, T.A.,Thang, P.D.,Tran, Q.T.,Thanh, T.D.,Phuc, N.X.,Phan, M.H.,Huy, B.T.,Yu, S.C. Elsevier 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.615 No.-

<P><B>Abstract</B></P> <P>We have determined the values of critical exponents of two polycrystalline samples (Nd<SUB>1−</SUB> <I> <SUB>x</SUB> </I>Y<I> <SUB>x</SUB> </I>)<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> (<I>x </I>=0 and 0.07) from the magnetization data versus temperature and magnetic field, <I>M</I>(<I>H</I>, <I>T</I>), to learn about their magnetic and magnetocaloric (MC) properties. The results reveal the samples exhibiting the crossover of first-order and second-order phase transitions, where the exponent values <I>β </I>=0.271 and <I>γ </I>=0.922 for <I>x </I>=0, and <I>β </I>=0.234–0.236 and <I>γ </I>=1.044–1.063 for <I>x </I>=0.07 determined by using modified Arrott plots and static-scaling hypothesis are close to those expected for the tricritical mean-field theory (<I>β </I>=0.25 and <I>γ </I>=1.0). Particularly, the <I>T</I> <SUB>C</SUB> of <I>x </I>=0 and 0.07 can be any value in the temperature ranges of 240–255K and 170–278K, respectively, depending on the magnitude of applied magnetic field and determination techniques. Around the <I>T</I> <SUB>C</SUB>, studying the MC effect of the samples has revealed a large magnetic-entropy change (Δ<I>S</I> <SUB>m</SUB>) up to ∼8J/kgK for the applied field interval Δ<I>H </I>=50kOe, corresponding to refrigerant capacity values of 200–245J/kg. These phenomena are related to the crossover nature and the persisting of FM/anti-FM interactions even above the <I>T</I> <SUB>C</SUB>, as further confirmed by electron-spin-resonance data, Curie–Weiss law-based analyses, and an exponential parameter characteristic of magnetic order <I>n </I>=dLn|Δ<I>S</I> <SUB>m</SUB>|/dLn<I>H</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Tricritical point in Y-doped Nd<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> manganites. </LI> <LI> A large magnetic-entropy change. </LI> <LI> Magnetic inhomogeneity and phase separation. </LI> </UL> </P>

ESR study of La_1–xPb_xMnO₃ (0.1 ≤ x ≤ 0.5) perovskites

Phan, T. L.,Min, S. G.,Phan, M. H.,Ha, N. D.,Chau, N.,Yu, S. C. Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.

<P>Electron spin resonance (ESR) spectra of La<SUB>1–x </SUB>Pb<SUB>x </SUB>MnO<SUB>3</SUB> (0.1 ≤ x ≤ 0.5) compounds were recorded at different temperatures. Asymmetrical and distored resonance signals due to ferromagnetic correlations at temperatures T < T<SUB>min</SUB> became Lorentzian at T > T<SUB>min</SUB>, where T<SUB>min</SUB> is the temperature corresponding to the narrowest ESR linewidth. The ESR linewidth with respect to temperature, ΔH (T), for the samples was fitted to the one-phonon process, ΔH (T) = A + BT. We found that B decreased from 5.45 Oe/K for x = 0.1 to 4.61 Oe/K for x = 0.5, indicating the decrease of lattice distortions with the Pb addition. The tem- perature dependence of the ESR intensity, I (T), for the samples was described well to an expression of I (T) = I<SUB>0</SUB> exp (E<SUB>a</SUB>/k<SUB>B</SUB>T). In the high-temperature region, 1/I (T) obeyed the Curie–Weiss law. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Improving mechanical and magnetocaloric responses of amorphous melt-extracted Gd-based microwires via nanocrystallization

Belliveau, H.F.,Yu, Y.Y.,Luo, Y.,Qin, F.X.,Wang, H.,Shen, H.X.,Sun, J.F.,Yu, S.C.,Srikanth, H.,Phan, M.H. Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.692 No.-

<P><B>Abstract</B></P> <P>We report on the structural, mechanical, and magnetocaloric properties of annealed melt-extracted Gd<SUB>53</SUB>Al<SUB>24</SUB>Co<SUB>20</SUB>Zr<SUB>3</SUB> amorphous microwires of ∼70 μm diameter. During heat treatment small islands of nanocrystallities are generated and isolated in the amorphous region for the wires. The size of the nanocrystallities ranges from 5 nm to 10 nm. The observed lattice distortion from the nanocrystallities causes changes in the magnetic properties of the wires. The annealing temperature of 100 °C has the largest strength (1845 MPa) as compared to wires annealed at other temperatures. This is likely to trigger nanophase transformation in the amorphous region and these nanocrystals have been preserved through the increase of annealing temperature. The formulation of the nanocrystalline islands is also verified by the selected-area electron diffraction (SAED). The microwires exhibit a large and reversible magnetocaloric effect (MCE), with the maximum isothermal magnetic entropy change (−Δ<I>S</I> <SUB>M</SUB>) and refrigerant capacity (<I>RC</I>) values of 9.5 J/kg K and 689 J/kg respectively for the microwire annealed at 100 °C. This <I>RC</I> is about 35%, 67%, and 91% larger than those of bulk Gd<SUB>53</SUB>Al<SUB>24</SUB>Co<SUB>20</SUB>Zr<SUB>3</SUB> (∼509 J/kg), Gd (∼410 J/kg), and Gd<SUB>5</SUB>Si<SUB>2</SUB>Ge<SUB>1.9</SUB>Fe<SUB>0.1</SUB> (∼360 J/kg) regardless of their ordering temperatures. These results demonstrate the ability to tune the mechanical and magnetic properties of the microwires by thermal annealing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The impact of nanocrystallization in Gd<SUB>53</SUB>Al<SUB>24</SUB>Co<SUB>20</SUB>Zr<SUB>3</SUB> microwires. </LI> <LI> Enhanced mechanical strength. </LI> <LI> Enhanced magnetocaloric response. </LI> </UL> </P>

N-geranyl cyclopropyl-carboximide modulates salty and umami taste in humans and animal models

Dewis, M.L.,Phan, T.-H.T.,Ren, Z.,Meng, X.,Cui, M.,Mummalaneni, S.,Rhyu, M.-R.,DeSimone, J.A.,Lyall, V. AMERICAN PHYSIOLOGICAL SOCIETY 2013 journal of neurophysiology Vol.109 No.2

The neuroprotective effect of eupatilin against ischemia/reperfusion-induced delayed neuronal damage in mice

Cai, M.,Phan, P.T.T.,Hong, J.G.,Kim, D.H.,Kim, J.M.,Park, S.J.,Liu, X.,Han, J.E.,Park, H.,Choi, J.W.,Ryu, J.H. North-Holland ; Elsevier Science Ltd 2012 european journal of pharmacology Vol.689 No.1

Eupatilin, a pharmacologically active flavone derived from the Artemisia plant species, has been reported to have anti-oxidant, anti-inflammatory, anti-allergic, and anti-tumor activities. In the present study, we investigated whether eupatilin exhibits neuroprotective activities against ischemia/reperfusion-induced delayed neuronal injury in mice. Transient global cerebral ischemia was induced in mice by bilateral common carotid artery occlusion (BCCAO) for 15min followed by reperfusion for 4 days. Eupatilin (1, 3, or 10mg/kg, p.o.) was administered immediately after the reperfusion. Histochemical studies showed that eupatilin (10mg/kg) increased the number of viable cells detected by Nissl staining and decreased the number of degenerating neuronal cells detected by Fluoro-Jade B staining in the hippocampal CA1 region. Western blotting indicated that eupatilin further increased the level of Akt phosphorylation at 8h after BCCAO. Furthermore, wortmannin, a phosphatidylinositol 3-kinase inhibitor, attenuated the eupatilin-induced increase of Akt phosphorylation. In addition, wortmannin completely reversed the eupatilin-induced neuroprotective effects observed at 4 days after reperfusion. These findings suggest that eupatilin is a promising therapeutic agent against global cerebral ischemia-induced neuronal damage and that its neuroprotective effects may be mediated in part by increased Akt phosphorylation.