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Phan, T.L.,Dang, N.T.,Ho, T.A.,Manh, T.V.,Thanh, T.D.,Jung, C.U.,Lee, B.W.,Le, A.T.,Phan, A.D.,Yu, S.C. Elsevier Sequoia 2016 Journal of alloys and compounds Vol.657 No.-
We have prepared polycrystalline samples La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Ba<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0, 0.025, 0.05, 0.075 and 0.1) by solid-state reaction, and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field (M-H-T) measurements. Experimental results reveal the easiness in tuning the Curie temperature (T<SUB>C</SUB>) from 260 to about 300 K by increasing Ba-doping concentration (x) from 0 to 0.1. Under an applied field H = 50 kOe, maximum magnetic-entropy changes around T<SUB>C</SUB> of the samples can be tuned in the range between 6 and 11 J kg<SUP>-1</SUP> K<SUP>-1</SUP>, corresponding to refrigerant-capacity values ranging from 190 to 250 J kg<SUP>-1</SUP>. These values are comparable to those of some conventional MC materials, and reveal the applicability of La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Ba<SUB>x</SUB>MnO<SUB>3</SUB> materials in magnetic refrigeration. Analyses of the critical behavior based on the Banerjee criteria, Arrott plots and scaling hypothesis for M-H-T data prove a magnetic-phase separation when Ba-doping concentration changes. In the doping region x = 0.05-0.075, the samples exhibits the crossover of first- and second-order phase transitions with the values of critical exponents β and γ close to those expected for the tricritical mean-field theory. The samples with x < 0.05 and x > 0.075 exhibit first- and second-order transitions, respectively. More detailed analyses related to the Griffiths singularity, the critical behavior for different magnetic-field intervals started from 10 kOe, and the magnetic-ordering parameter n = dLn|ΔS<SUB>m</SUB>|/dLnH (where ΔS<SUB>m</SUB> is the magnetic-entropy change) demonstrate magnetic inhomogeneities and multicritical phenomena existing in the samples.
Phan, T. L.,Nguyen, V. D.,Ho, T. A.,Khiem, N. V.,Thanh, T. D.,Phuc, N. X.,Thang, P. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.6
<P>The magnetic properties of polycrystalline ceramic samples (Nd1-xYx)(0.7)Sr0.3MnO3 with x = 0.21 - 0.35 were studied by means of dc magnetization and ac susceptibility measurements. Experimental results reveal a strong decrease of the ferromagnetic (FM)-paramagnetic phase-transition temperature (T-C) from 97 to 65 K as increasing x from 0.21 to 0.35, respectively. There is magnetic inhomogeneity associated with short-range FM order. Particularly, the samples undergo a spin-glass (SG) phase transition at the so-called blocking temperature (T-B) below T-C, which shifts toward lower temperatures with increasing the applied field, Hex; T-B -> T-g (the SG phase-transition temperature) as H-ex -> 0. The existence of the SG behavior in these samples was also confirmed by frequency (f) dependences of the ac susceptibility. For the in-phase/real component, chi' (T), it shows a frequency-dependent peak at the SG freezing temperature (T-f); T-f -> T-g as f -> 0. Dynamics of this process were analyzed by means of the slowing down scaling law, tau/tau(0) proportional to (T-f/T-g - 1)(-zv), where tau(0) and zv are the characteristic time and critical exponent, respectively. Fitting the experimental T-f(f) data to the scaling law gave the results of zv = 10.1-12.3 and tau(0) = 10(-21)-10(-15)s. These values are different from those expected for canonical SG systems with zv = 10 and tau(0) = 10(-13)s, revealing the cluster-SG behavior of (Nd1-xYx)(0.7)Sr0.3MnO3 samples. Notably, the increase in Y content leads to the shift of tau(0) and zv values toward those of canonical SG systems, which is ascribed to an expansion of SG clusters.</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>
Phan, T. L.,Thanh, T. D.,Ho, T. A.,Manh, T. V.,Tran, Q. T.,Lampen, P.,Phan, M. H.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>This paper points out that the magnetic-phase transition and magnetocaloric effect of La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> (LCMO) can be easily controlled by using the mechanical milling method. Changing the milling time from 5 to 30 min, we have obtained LCMO nanoparticles (NPs) with average crystallite sizes (d, determined by the Williamson-Hall method) ranging from 100 to 45 nm. The magnetic studies (based on a superconducting quantum interference device) and simple analyses (based on Banerjee's criteria) prove the magnetic-phase transformation from the first-order to the second-order, which takes place at a threshold value of d located in the range 60-70 nm. Compared with the as-prepared LCMO sample (a first-order magnetic phase transition), though the d decrease reduces the values of the T<SUB>C</SUB>, magnetization, magnetic-entropy change, and refrigerant capacity, but the width of the magnetic phase transition is increased remarkably. This widens the working range of LCMO NPs in magnetic refrigeration applications. We believe that the presence of surface-related effects, lattice strain, and distortions leads to Mn<SUP>3+</SUP>-Mn<SUP>4+</SUP> ferromagnetic interactions in LCMO NPs weaker than that in the as-prepared sample.</P>
Phan, T. L.,Thanh, P. Q.,Chau, N.,Huu, C. X.,Ngo, D.-T,Ho, T. A.,Thanh, T. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>Though many previous works focused on studying Cr-doped Fe-Si-Nb-B-Cu amorphous alloys, magnetic-interaction mechanisms in these materials have not been carefully investigated yet. Dealing with these issues, we have prepared the amorphous alloy ribbons Fe<SUB>78-x</SUB>Cr<SUB>x</SUB>Si<SUB>4</SUB>Nb<SUB>5</SUB>B<SUB>12</SUB>Cu<SUB>1</SUB> with x= 1, 3, and 6, and then studied their magnetic and critical properties. Magnetization versus temperature and magnetic-field measurements, MHT, performed on a vibrating sample magnetometer reveal that the Cr-content increase in Fe<SUB>78-x</SUB>Cr<SUB>x</SUB>Si<SUB>4</SUB>Nb<SUB>5</SUB>B<SUB>12</SUB>Cu<SUB>1</SUB> reduces the T<SUB>C</SUB> from 430 K for x= 1 to about 322 K (for x= 6). This indicates the decline of ferromagnetic (FM) exchange interactions between Fe atoms when there is the presence of Cr atoms. We have also analyzed the M(H) data at the temperatures in the vicinity of the T<SUB>C</SUB> using the modified Arrott plot method and the scaling hypothesis, and determined the values of the critical exponents β = 0.367-0.376 and γ = 1.315-1.338. These values are close to those expected for the 3-D Heisenberg model with β = 0.365 and γ = 1.336, proving the existence of short-range FM order in the amorphous alloy ribbons.</P>
( Thanh T. Ho ),( Chi P. Pham ) 부산외국어대학교 아세안연구원 2023 Suvannabhumi Vol.15 No.2
Many publications of ecocritical research papers and translations of ecocriticism occur in Vietnam in recent years. This paper examines ecocritical scholarly writing in Vietnam, understanding how it corresponds to―reflects and attends to ―contemporary Vietnamese society and politics. Specifically, this paper contextualizes Vietnamese ecocriticism in contemporary social and political concerns―embodied in journalistic and administrative documents―about the modernity-oriented postcolonial nation-building of Vietnam. In revealing critiques of political and social degenerations implied in ecocritical writings in Vietnam, this paper suggests that the emergence of ecocriticism in present-day Vietnam indicates a recent “political turn.” More importantly, such emergence reflects and engages with the continuing Marxist perspective of literature as an instrument for social criticism and cultural revolution in Vietnam. Vietnamese ecocritics bear the mission of prophets of the time, public educators, and soul engineers, writing is an act of engaging with and influencing reality. Writing (literary and scholarly) still forms an idealized ideological instrument in the struggles for national homogeneity and sovereignty and social democracy in present-day Vietnam.