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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>
Tho, P.T.,Clements, E.M.,Kim, D.H.,Tran, N.,Osofsky, M.S.,Phan, M.H.,Phan, T.L.,Lee, B.W. Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.741 No.-
<P><B>Abstract</B></P> <P>We have studied the crystal structure and magnetic properties of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>1-x</SUB>Ti<SUB>x</SUB>O<SUB>3</SUB> (<I>x</I> = 0.02–0.1) at the morphotropic phase boundary of <I>R</I>3<I>c</I>, <I>Imma</I>, and <I>Pbam</I> phases. The results of Rietveld-refined X-ray diffraction patterns reveal the existence of multi-phase structures, including <I>R</I>3<I>c</I> + <I>Imma</I> for <I>x</I> = 0.02–0.06 and <I>Imma + Pbam</I> for <I>x</I> = 0.08–0.1. The studies of Raman scattering spectra indicate a structural transformation through the disappearance of typical <I>R</I>3<I>c</I> modes. This strongly influences the magnetic properties that are dependent on the crystalline phase ratio. In particular, the magnetic coercivity of <I>x</I> = 0.04–0.06 drastically changes when the <I>Imma</I> phase is dominant. A mechanism of magnetic interactions occurring at the phase boundary is proposed to explain the features of magnetic hysteresis loops of the compounds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Crystal structure of (La,Ti)-codoped BiFeO<SUB>3</SUB> at morphotropic phase boundary. </LI> <LI> Magnetic properties are strongly dependent on the phase ratio of two crystal structures. </LI> <LI> Magnetic interactions at the phase boundary were explained. </LI> <LI> The vertical hysteresis shift (exchange bias) is related to the pinned spin at the phase boundary. </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>
Tho, P.T.,Dang, N.V.,Nghia, N.X.,Khiem, L.H.,Xuan, C.T.A.,Kim, H.S.,Lee, B.W. Elsevier 2018 The Journal of physics and chemistry of solids Vol.121 No.-
<P><B>Abstract</B></P> <P>In this investigation, we have studied the crystal structure and magnetic properties of Zn doped Bi0.84La0.16FeO3 (<I>x</I> = 0.02–0.1) ceramics at the morphotropic phase boundary of rhombohedral and orthorhombic phases. Rietveld refinement of the obtained XRD patterns and Raman spectroscopy confirm the presence of multiphases crystal structure of <I>R3c</I> rhombohedral and <I>Pbam</I> orthorhombic. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization and coercivity with dominating of orthorhombic phase. The isothermal structural transition from <I>R3c</I> to <I>Pbam</I> is caused for the decrease in magnetization and the increase in coercivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal structure of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>1-x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> at the morphotropic phase boundary. </LI> <LI> The microstructure reveals the coexistence crystal phase and their phase boundary. </LI> <LI> The isothermal structural transition induces the change in magnetic properties. </LI> <LI> The vertical shift (exchange bias) is observed in compounds. </LI> </UL> </P>
Tho, P.T.,Kim, D.H.,Phan, T.L.,Dang, N.V.,Lee, B.W. Elsevier 2018 Journal of magnetism and magnetic materials Vol.462 No.-
<P><B>Abstract</B></P> <P>We have studied the vertical hysteresis shift, the exchange bias, and the exchange spring effect in a polycrystalline sample of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>0.96</SUB>Ti<SUB>0.04</SUB>O<SUB>3</SUB> at morphotropic phase boundary. The magnetic coupling at the phase boundary causes the formation of pinned spin region, which induces the spin rotation inside the two structural phases. The exchange coupling between the pinned spin and the two phases act as hard/soft coupling layers, respectively. Dependence on the strength of the spin pinning, we observed various types of the exchange coupling at different temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The phase boundary is directly separated two crystal structures into two grain size regions. </LI> <LI> High-temperature magnetic measurement is used to study the magnetic properties and magnetic interactions. </LI> <LI> The vertical hysteresis shift, the exchange bias, and the exchange spring effects are observed at different temperature and applied field conditions. </LI> <LI> The spin pinning at the phase boundary is explained for the various types of magnetic coupling and hysteresis behaviors. </LI> </UL> </P>