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  • Article


  • Authors: Phung, ThanhPQ (2014)

  • We used Banerjee0 s criteria, modified Arrott plots, and the scaling hypothesis to analyze magneticfield dependences of magnetization near the ferromagnetic–paramagnetic (FM–PM) phasetransition temperature (TC) of perovskite-type manganites La0.7Ca0.3Mn1 x NixO3(x¼0.09, 0.12 and 0.15). In the FM region, experimental results for the critical exponentβ(¼0.171 and 0.262 for x¼0.09 and 0.12, respectively) reveal twofirst samples exhibiting tricriticality associated with the crossover offirst- and second-order phase transitions. Increasing Ni-doping content leads to the shift of theβvalue (¼0.320 forx¼0.15) towards that expected for the 3D Ising model (β¼0.325). This is due to the fact that the substitution of Ni ions into the Mn site changes structural parameters and dilutes the...

  • Article


  • Authors: Phung, ThanhPQ (2006)

  • Amorphous soft magnetic ribbons Fe73.5 xCrxSi13.5B9Nb3Cu1 (x¼1–5) have been fabricated by rapid quenching on a single copper wheel. The differential scanning calorimetry (DSC) patterns showed that the crystallization temperature ofa-Fe(Si) phase is ranging from 542 to 5691C, a little higher than that of pure Finemet (x¼0). With the same annealing regime, the crystallization volume fraction as well as the particle size ofa-Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in studied samples. Especially, the interesting fact is that the laminar structure of heat-treated ribbons on the surface contacted to copper wheel in the fabricating process has been firstly discovered and explained to be related to the existence of Cr in studied samples. The hysteres...

  • Article


  • Authors: Phung, ThanhPQ (2004)

  • Ca1 xPrxMnO3 d (x=0, 0.05, 0.15, 0.1, 0.2, 0.4, 0.67;d=0.02) samples were prepared by a solid-state reaction method. X-ray diffraction analysis showed that all samples prepared were of single phase with orthorhombic structure. Electrical resistivity measurements from room temperature to 1300 K showed that a metallic conducting tendency dominated at high temperatures. The hopping nature of the charge carriers was well interpreted in the framework of polaron theory. The Seebeck coefficient was measured in the same temperature interval, and its concentration dependence was analyzed using the high-temperature (HT) thermopower theory proposed by Marsh–Parris. The thermal conductivity and the figure of merit of the prepared samples were also compared with those of other similar per...

  • Article


  • Authors: Phung, ThanhPQ (2012-04)

  • We have studied the influence of the Cu-doping on the critical properties of a polycrystalline sample of prepared by solid-state reaction. Analyses of static magnetization data in the vicinity of the ferromagnetic-paramagnetic phase transition based on the modified Arrott plot reveal critical parameters of , and .These parameters are in good agreement with a magnetic equation of state , where (the reduced temperature), for and for . Comparing with theoretical models, the critical exponents in our case are close to those expected for the mean-field theory. This reflects that the Cu doping leads to the second-order phase transition in while the parent compound of exhibits the first-order phase...

  • Article


  • Authors: Phung, ThanhPQ (2007)

  • The excellent agreement with experimental data has been achieved in fitting the resistivity of doped manganate–ruthenates for whole temperature range. The analysis interpreted the resistivity in terms of percolation of carriers through the system of grain boundaries, having been assumed as the conductive fractal medium. The percolative conduction regime has been shown substantial for the K-doped ruthenates [H.N. Nhat, H.D. Chinh and M.H. Phan, Solid State Commun. 139 (2006) 456], and we confirm here that this approach also correctly discusses the unusual semiconductor-like behaviours of the doped manganate–ruthenates

  • Article


  • Authors: Phung, ThanhPQ (2013)

  • We have studied the critical behavior and magnetocaloric effect of a perovskite-type manganite LaMn0.9Fe0.1O3with a second-order phase transition. Detailed critical analyses based on the modified Arrott plot method and the universal scaling law gave the critical parameters TC≈135.7 K, β¼0.35870.007, γ¼1.32870.003, and δ¼4.7170.06. Comparing to standard models, the critical exponent values determined in our work are close to those expected for the 3D Heisenberg model (withβ¼0.365,γ¼1.336, andδ¼4.80). This reflects an existence of ferromagnetic short-range order in LaMn0.9Fe0.1O3. Around TC, the magnetic entropy change reaches the maximum value (ΔSmax), which is about 3.8 J kg−1 K−1 for the appliedfield of 50 kOe. Particularly, its magnetic-field dependence obeys the power law...

  • Article


  • Authors: Phung, ThanhPQ (2007)

  • Single-phase perovskite compounds Ca0.6Pr0.4Mn1 yRuyO3 (y¼0, 0.03, 0.05, 0.07) were prepared by ceramic-technology method. Thermomagnetic plots, temperature dependence of resistivities, ac-susceptibilities of the produced samples were determined. The nonruthenium doping (y¼0) sample presents charge-ordering phenomenon at TCO¼291 K. The experiment results show that the ruthenium doping destroys the charge ordering state, enhances ferromagnetism tendency and conductivity

  • Article


  • Authors: Phung, ThanhPQ (2012-11)

  • CaMnO3 is an antiferromagnet, in which the super-exchange interaction taking place between Mn4+ ions plays an important role. The doping of a small amount of 15% Pr into the Ca site, Ca0.85Pr0.15MnO3, leads to the appearance of Mn3+ ions, and introduces the ferromagnetic (FM) double-exchange interaction between Mn3+ and Mn4+ ions, which is dominant in a narrow temperature range of 90 ∼ 115 K. The FM interaction becomes strong for Ca0.85Pr0.15MnO3 doped with 4 and 8% Ru into the Mn site (i.e., Ca0.85Pr0.15Mn1−xRuxO3 with x = 0.04 and 0.08). The Curie temperature obtained for x = 0.04 and 0.08 are about 135 and 180 K, respectively. While the FM interaction in the former is dominant due to Mn3+-Mn4+ exchange pairs, the latter has the contribution of Ru ions. This results in remar...

  • Article


  • Authors: Phung, ThanhPQ (2012)

  • The magnetic and transport properties of the perovskites La0.67Ca0.33Mn1-xTMxO3 were found to be sufficiently changed with the substitution of Mn-sites by other 3d transition-metal cations (TM¼Cu,Zn; x¼0.15). The values ofTC, TM I, and TCMRwere surveyed when Mn was replaced by Cu and Zn. The magnetic field induced resistivity and magnetic entropy change of these samples showed abrupt changes nearTC(194.2 and 201.5 K for Cu and Zn-doped case respectively) and attained the highest values among the doped cases (up to 20% Cu). The maximum values (obtained at H¼4 kOe) of magnetoresistance ratio (CMR) were 27.8%, and 24.5% and of magnetic entropy change ( DSM)were 3.9 and 3.2 J/kg K for Cu and Zn-doped, respectively