Coexistence and Conversion of Phases in Ti-Doped Manganite Observed by Magnetization and Transport Measurements

Le Viet Bau,Nguyen Van Khiem,Dao Nguyen Hoai Nam,,Nguyen Xuan Phuc 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5

The La0.7Sr0.3Mn₁-xTixO₃ (x = 0 ~ 0.3) compounds were studied by using magnetic and transport measurements. The substitution of Ti⁴+ for Mn⁴+ reduces the transition temperature Tc and the saturation magnetization (Ms). By analyzing the M(H) curves in high-field regions, a coexistence of two separate phases (a ferromagnetic and a non-ferromagnetic one) is revealed in all the compounds. Moreover, a conversion between the two phases with temperature was observed; the volume fraction of the ferromagnetic phase decreases while that of non-ferromagnetic phase increases with increasing temperature. The results also suggest that the non-ferromagnetic phase develops with increasing Ti content. The La0.7Sr0.3Mn₁-xTixO₃ (x = 0 ~ 0.3) compounds were studied by using magnetic and transport measurements. The substitution of Ti⁴+ for Mn⁴+ reduces the transition temperature Tc and the saturation magnetization (Ms). By analyzing the M(H) curves in high-field regions, a coexistence of two separate phases (a ferromagnetic and a non-ferromagnetic one) is revealed in all the compounds. Moreover, a conversion between the two phases with temperature was observed; the volume fraction of the ferromagnetic phase decreases while that of non-ferromagnetic phase increases with increasing temperature. The results also suggest that the non-ferromagnetic phase develops with increasing Ti content.

Room Temperature Magnetocaloric Effect in <tex> ${\hbox{La}}_{0.7}{\hbox{Sr}}_{0.3}{\hbox{Mn}}_{1\hbox{-}{\rm x}}{\hbox{Co}}_{\rm x}{\hbox{O}}_{3}$</tex>

Tran Dang Thanh,Le Viet Bau,Phan, T. L.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.1

<P>We have investigated the magnetic properties and magnetocaloric effect in La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Mn<SUB>1-x</SUB>Co<SUB>x</SUB>O<SUB>3</SUB> prepared by a conventional solid-state reaction method. Magnetic measurements versus temperature revealed that the Curie temperature (T<SUB>C</SUB>) decreased gradually with increasing Co content (x); T<SUB>C</SUB> values are about 360, 310, 296 and 280 K for x =0.0, 0.06, 0.08 and 0.1, respectively. Magnetic entropy change (ΔS<SUB>m</SUB>) of the samples under a magnetic field change of 10 kOe was calculated by using isothermal magnetization data. We have found its maximum (|ΔS<SUB>max</SUB>|) achieved around T<SUB>C</SUB>, which is not changed much (~ 1.5 J·kg<SUP>-1</SUP>·K<SUP>-1</SUP>) with increasing Co-doping concentration. If combining the samples with x = 0.06, 0.08 and 0.10 for magnetic refrigeration, particularly, the temperature range can be used in between 266 K and 322 K, where |ΔS<SUB>max</SUB>| values are stable at about 0.98 J·kg<SUP>-1</SUP>·K<SUP>-1</SUP>. The relative cooling power is accordingly about 55 J·kg<SUP>-1</SUP> and comparable to that of other magnetocaloric alloys. These results suggest La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Mn<SUB>1-x</SUB>Co<SUB>x</SUB>O<SUB>3</SUB> compounds to be a potential candidate for magnetic refrigerators at room temperature.</P>

Influence of Crystallite Size on Magnetocaloric Effect and Critical Behavior La_0.7Sr_0.3Mn_0.92Co_0.08O₃ Nanoparticles

Tran Dang Thanh,Dinh Chi Linh,Le Viet Bau,Thi Anh Ho,Tien Van Manh,The-Long Phan,Seong-Cho Yu IEEE 2015 IEEE transactions on magnetics Vol.51 No.1

<P>Four samples of La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Mn<SUB>0.92</SUB>Co<SUB>0.08</SUB>O<SUB>3</SUB> (LSMCO) with different crystallite sizes were prepared by the combination of solid-state reaction and mechanical milling methods. Based on isothermal magnetization data, M(H), temperature dependences of magnetic entropy change, ΔS<SUB>m</SUB>T, of the samples under a magnetic field change of 10 kOe were calculated. The maximum values of magnetic entropy change (|ΔS<SUB>max</SUB>|) at room temperature are in the range of 0.9-1.4 J · kg<SUP>-1</SUP> · K<SUP>-1</SUP>, corresponding to ferromagnetic (FM)-paramagnetic phase transition. In addition, M<SUP>2</SUP> versus H/M curves at temperatures around TC prove the samples exhibiting a second-order magnetic phase transition. The critical exponents β, γ, and δ were determined using the modified Arrott plot method and critical isotherm analysis. Here, these exponent values are located in between those expected for the mean-field theory and 3-D Heisenberg model. It means the coexistence of short-range and long-range FM interactions in LSMCO nanoparticles.</P>

Magnetic and magnetocaloric properties in second-order phase transition La_1−xK_xMnO₃ and their composites

Thanh, Tran Dang,Linh, Dinh Chi,Yen, Pham Duc Huyen,Bau, Le Viet,Ky, Vu Hong,Wang, Zhihao,Piao, Hong-Guang,An, Nguyen Manh,Yu, Seong-Cho Elsevier 2018 PHYSICA B-CONDENSED MATTER - Vol.532 No.-

<P><B>Abstract</B></P> <P>In this work, we present a detailed study on the magnetic properties and the magnetocaloric effect (MCE) of La<SUB>1−x</SUB>K<SUB>x</SUB>MnO<SUB>3</SUB> compounds with <I>x</I>=0.05–0.2. Our results pointed out that the Curie temperature (<I>T</I> <SUB>C</SUB>) could be controlled easily from 213 to 306K by increasing K-doping concentration (<I>x</I>) from 0.05 to 0.2. In the paramagnetic region, the inverse of the susceptibility can be analyzed by using the Curie-Weiss law, <I>χ</I>(<I>T</I>)=<I>C</I>/(<I>T</I>−<I>θ</I>). The results have proved an existence of ferromagnetic clusters at temperatures above <I>T</I> <SUB>C</SUB>. Based on Banerjee's criteria, we also pointed out that the samples are the second-order phase transition materials. Their magnetic entropy change was calculated by using the Maxwell relation and a phenomenological model. Interestingly, the samples with <I>x</I>=0.1–0.2 exhibit a large MCE in a range of 282–306K, which are suitable for room-temperature magnetic refrigeration applications. The composites obtained from single phase samples (<I>x</I>=0.1–0.2) exhibit the high relative cooling power values in a wide temperature range. From the viewpoint of the refrigerant capacity, the composites formed out of La<SUB>1−x</SUB>K<SUB>x</SUB>MnO<SUB>3</SUB> will become more useful for magnetic refrigeration applications around room-temperature.</P>

Critical Behavior in La_0.75Ca_0.2Ag_0.05MnO₃ Exhibiting the Griffiths Phase

Thanh, Tran Dang,Huyen Yen, Pham Duc,Hau, Kieu Xuan,Bau, Le Viet,Yu, S. C. IEEE 2018 IEEE transactions on magnetics Vol.54 No.11

<P>In this paper, we have investigated the critical properties in the vicinity of the ferromagnetic (FM)–paramagnetic (PM) phase transition in a polycrystalline sample of La<SUB>0.75</SUB>Ca<SUB>0.2</SUB>Ag<SUB>0.05</SUB>MnO<SUB>3</SUB>, which was prepared by a solid-state reaction method. Temperature dependence of the inverse of the susceptibility <TEX>$\chi ^{-1}$</TEX> ( <TEX>$T$</TEX>) proves an existence of the Griffiths phase well above Curie temperature ( <TEX>$T_{C} = 230$</TEX> K). Detailed analyses of the isothermal magnetization <TEX>$M$</TEX>( <TEX>$H$</TEX>, <TEX>$T$</TEX>) data reveal the sample exhibiting a second-order magnetic phase transition, and its temperature dependences of the saturation magnetization and the initial susceptibility obey the asymptotic relations. Using the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, the critical parameters ( <TEX>$\beta$</TEX>, <TEX>$\gamma$</TEX>, <TEX>$\delta$</TEX>, and <TEX>$T_{C}$</TEX>) of La<SUB>0.75</SUB>Ca<SUB>0.2</SUB>Ag<SUB>0.05</SUB>MnO<SUB>3</SUB> compound have been estimated. Using these critical exponent values, almost <TEX>$M$</TEX>( <TEX>$H$</TEX>, <TEX>$T$</TEX>) data measured at different temperatures around FM–PM phase transition are collapsed onto two universal curves of <TEX>$M/\vert \varepsilon \vert ^{\boldsymbol {\beta }}$</TEX> versus <TEX>$H/\vert \varepsilon \vert ^{\boldsymbol {\beta }+\boldsymbol {\gamma }}$</TEX> corresponding to the regular functions for <TEX>$T > T_{C}$</TEX> and <TEX>$T < T_{C}$</TEX>, respectively.</P>

Na-doped La_0.7Ca_0.3MnO₃ compounds exhibiting a large magnetocaloric effect near room temperature

Chi Linh, Dinh,Thi Ha, Nguyen,Huu Duc, Nguyen,Giang Nam, Le Huu,Bau, Le Viet,Manh An, Nguyen,Yu, Seong-Cho,Dang Thanh, Tran Elsevier 2018 PHYSICA B-CONDENSED MATTER - Vol.532 No.-

<P><B>Abstract</B></P> <P>In this work, we have investigated the magnetic properties and the magnetocaloric effect of La<SUB>0.7−x</SUB>Na<SUB>x</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> compounds, which were prepared by a conventional solid-state reaction technique. The Rietveld refinement results suggested that the samples are single phase belonging to an orthorhombic structure (space group <I>Pnma</I>). Analyzing temperature dependence of magnetization <I>M</I>(<I>T</I>) revealed that the Curie temperature (<I>T</I> <SUB>C</SUB>) increases with increasing Na content (<I>x</I>). Their <I>T</I> <SUB>C</SUB> value is found to be 260–298K for <I>x</I>=0.0–0.1, respectively. Base on <I>M</I>(<I>T</I>) data measured at different applied magnetic fields (<I>H</I>), temperature dependence of magnetic entropy change Δ<I>S</I> <SUB>m</SUB>(<I>T</I>) data for all the samples was calculated by using a phenomenological model. In the vicinity of <I>T</I> <SUB>C,</SUB> -Δ<I>S</I> <SUB>m</SUB>(<I>T</I>) curve reaches a maximum value (denoted as |Δ<I>S</I> <SUB>max</SUB>|), which gradually increases with increasing <I>H</I>. Under 12kOe, the value of |Δ<I>S</I> <SUB>max</SUB>| is in a range of 1.47–5.19J/kgK corresponding to the relative cooling power RCP=57.12–75.88J/kg. Applied the universal master curve method for the magnetic entropy change, we concluded that Na-doped in La<SUB>0.7−x</SUB>Na<SUB>x</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> compounds leads to modification the nature of the magnetic phase transition from the first- to the second-order.</P>

Magnetocaloric Effect in La_0.7Ca_0.25Ba_0.05MnO₃ Nanocrystals Exhibiting the Crossover of First- and Second-Order Magnetic Phase Transformation

Thanh, Tran Dang,Linh, Dinh Chi,Van, Hoang Thanh,Ho, Thi Anh,Van Manh, Tien,Bau, Le Viet,Phan, The-Long,Yu, Seng-Cho The Japan Institute of Metals 2015 MATERIALS TRANSACTIONS Vol.56 No.9