Showing papers by "Tran Dang Thanh published in 2013"
TL;DR: In this paper, a detailed study of the properties of the ferromagnetic to paramagnetic transition in polycrystalline manganites La 1− x Ca x MnO 3 ( x = 0.2, 0.3, and 0.4) is presented.
83 citations
TL;DR: In this paper, an alternate method based on mechanical milling was proposed to induce defect-related ferromagnetism in ZnO nanoparticles (NPs) from initial diamagnetic powders.
Abstract: Though ZnO is known as a diamagnetic material, recent studies have revealed that its nanostructures can be ferromagnetic (FM). The FM origin has been ascribed to intrinsic defects. This work shines light on an alternate method based on mechanical milling to induce defect-related ferromagnetism in ZnO nanoparticles (NPs) from initial diamagnetic ZnO powders. Our idea is motivated by the fact that mechanical milling introduces more defects to a ground material. We point out that the FM order increases with increasing the density of defects in ZnO NPs. The experimental results obtained from analyzing X-ray absorption, electron spin resonance, and Raman scattering spectra demonstrate that the ferromagnetism in ZnO NPs is due to intrinsic defects mainly related to oxygen and zinc vacancies. Among these, zinc vacancies play a decisive role in introducing a high FM order in ZnO NPs.
82 citations
TL;DR: Results indicate the CZMMs are potential chiral nanomaterials for enantioseparations and have shown an excellent recyclability and can be used for further chiral separations of different kinds of racemates.
Abstract: Separation of enantiomers of a chiral compound is one of the most interesting and challenging tasks because of their identical physical and chemical properties. Magnetic materials possessing chiral functionality on their surface can not only exhibit magnetic properties but also recognize chirality. Fe3O4@ZrO2 core–shell nano-materials have not been reported previously for chiral separation of racemates. Zirconia has been shown to be the most stable oxide mechanically, thermally and chemically, and shows better physical and chemical properties among inorganic metal oxides. The present work explores core–shell microspheres consisting of a Fe3O4 magnetic core covered by a zirconia shell (Fe3O4@ZrO2) which are immobilized with cellulose tris(3,5-dimethylphenylcarbamate) to get chiral zirconia magnetic microspheres (CZMMs). As-synthesized CZMMs have been applied for the separation of racemic chiral drugs and the results indicate the CZMMs are potential chiral nanomaterials for enantioseparations. Most importantly the synthesized CZMMs have shown an excellent recyclability and can be used for further chiral separations of different kinds of racemates.
40 citations
TL;DR: In this article, the authors investigated the magnetic properties of nanostructured BaTiO3 materials and found that the ferromagnetic order increases with increasing the density of defects, and that the defect density can be changed upon the milling time.
Abstract: Recent studies have pointed out an existence of the room-temperature ferromagnetism in nanostructured BaTiO3 materials. It has been thought that the ferromagnetism is due to intrinsic defects. To elucidate this issue, we have prepared BaTiO3 nanoparticles by mechanical milling, starting from diamagnetic/nonmagnetic BaTiO3 powders, and then investigated their magnetic properties. Our idea is motivated by the fact that the mechanical milling introduces more lattice defects to a ground material. If so, the ferromagnetic (FM) order will increase with increasing the density of defects. Here, the defect density can be changed upon the milling time (tm). Our magnetic measurements at 300 K have indicated that the FM order increases with increasing tm as expected. To understand the nature of ferromagnetism, we studied X-ray absorption fine structure (XAFS) spectra of the samples for the Ti K-edge. The shift of the absorption edge towards lower energies of Ti3+ with increasing tm, proving an increase in Ti3+ concen...
32 citations
TL;DR: In this paper, the critical behavior and magnetocaloric effect of perovskite-type manganite LaMn09Fe01O3 with a second-order phase transition were studied.
26 citations
TL;DR: The magnetic properties and magnetocaloric effect in Fe90−xNixZr10 alloy ribbons prepared by rapid-quenching method have been reported in this article, which correspond to refrigerant capacity in the range of 86-334 J·kg−1 and are comparable to other known MC materials.
Abstract: We report magnetic properties and magnetocaloric (MC) effect in Fe90−xNixZr10 (x = 0, 5, 10, and 15) alloy ribbons prepared by rapid-quenching method. We found the Curie temperature (TC) of the alloy ribbons depends strongly on Ni-doping concentration (x) increasing from 245 K for (x = 0), through 306 K (for x = 5) up to TC = 403 (for x = 15). Also, the dependence of the maximum magnetic entropy change (|ΔSmax|) on Ni content was readily apparent. Indeed, for the x = 0 and 5 samples that have TC around room temperature, the |ΔSmax| values increment under magnetic field changes of 10, 20, and 40 kOe was found to be as high as 0.87, 1.76, and 3.04 J·kg−1·K−1 for x = 0, and 1.03, 1.90, and 3.26 J·kg−1·K−1 for x = 5, respectively. These values correspond to refrigerant capacity in the range of 86-334 J·kg−1 and are comparable to other known MC materials. High magnetocaloric performance in rare-earth-free non-expensive metallic alloys indicates that these materials could be competitive candidate for active mag...
17 citations
TL;DR: In this article, the phase transition width and magnetocaloric effect of Sm0.58Sr0.42MnO3 nanoparticles (NPs) were investigated.
16 citations
TL;DR: In this article, the Curie temperature of the alloys dramatically decreased from ∼960 K to room temperature at high quenching rates at high Ni concentration, which was suitable for applications in magnetic refrigerators at room temperature.
Abstract: Fe90−x Ni
x
Zr10 (x = 0, 5, 10, 15, 20 and 25) ribbons with various thicknesses were prepared by using a melt-spinning technique. The Curie temperature, T
C
, of the alloys dramatically decreased from ∼960 K to room temperature at high quenching rates. When the alloys had an amorphous structure, their T
C
strongly depended on the Ni concentration. The maximum entropy change, |ΔS
m
|
max
, with ΔH = 12 kOe, of the alloys was around 1 J·kg−1K−1 at room temperature. On the other hand, the full width at half maximum the entropy-change peak was quite large, ∼ 85 K, which was suitable for applications in magnetic refrigerators at room temperature.
12 citations
TL;DR: In this article, the magnetic properties and magnetocaloric effect of LaFe10−xBxSi3 (x,= 1, 2, and 3) alloy ribbons prepared by a rapidly quenching method were studied.
Abstract: We have studied the magnetic properties and magnetocaloric effect of LaFe10−xBxSi3 (x = 1, 2, and 3) alloy ribbons prepared by a rapidly quenching method. The partial replacement of Fe for B in LaFe10−xBxSi3 leads to a rapid decrease in the Curie temperature (TC) from 425 K for x = 1, through 310 K for x = 2, to 190 K for x = 3. Among LaFe10−xBxSi3 ribbons, only LaFe7B3Si3 (i.e., x = 3) has a dominancy of amorphous phase. The M2 versus H/M plots prove this sample exhibiting a second-order magnetic phase transition. The detailed analyses of M(H) data around TC based on the modified Arrott plot introduced critical values of TC ≈ 192 K, β = 0.354 ± 0.013, γ = 1.355 ± 0.032, and δ = 4.8 ± 0.1. These values are close to those expected for the 3D-Heisenberg model (β = 0.365 and γ = 1.336), indicating an existence of ferromagnetic short-range interactions. Concerning the magnetic entropy change (ΔSm), we have found its maximum ΔSm achieved just around TC, which are 1.04 and 1.42 J/kg K for x = 2 and 3, respectiv...
8 citations
TL;DR: In this article, the critical exponents determined for the ferromagnetic-to-paramagnetic phase transition by employing the Kouvel-Fisher method are not consistent with any universality classes, but in between the mean-field and 3D Heisenberg models.
Abstract: Disorder-induced collapse of the charge-ordered state was found in a half-hole-doped manganite Pr0.3Nd0.2Sr0.5MnO3 by means of studying the magnetic and critical behaviors. Large magnetic frustration originated from the strong competition between ferromagnetic and antiferromagnetic interactions led to the absence of long-range charge ordering. The critical exponents determined for the ferromagnetic-to-paramagnetic phase transition by employing the Kouvel-Fisher method are not consistent with any universality classes, but in between the mean-field and 3D Heisenberg models. It is suggested that the Pr/Nd-site disorder destabilizes the charge-ordered state, and breaks the long-range charge-ordering system into the fragment of antiferromagnetic clusters, which coexist with the ferromagnetic background. Such ionic disorder-induced highly magnetic inhomogeneity is responsible for the nonuniversal critical behavior.
8 citations
TL;DR: Based on the Landau phase transition theory and Banerjee's criteria, a polycrystalline sample of orthorhombic La0.7Ca 0.3Mn 0.15O3 was found to undergo a second-order magnetic phase transition as discussed by the authors.
Abstract: We prepared a polycrystalline sample of orthorhombic La0.7Ca0.3Mn0.85Ni0.15O3, and then studied its critical behavior. Based on the Landau phase-transition theory and Banerjee's criteria, we have found the sample undergoing a second-order magnetic phase transition. This continuous transition is characterized by critical parameters of TC = 170 K, β = 0.320 ± 0.009, γ = 0.990 ± 0.082, and δ = 4.09 ± 0.17 determined from modified Arrott plots. With these values, the magnetization-field-temperature (M-H-T) behaviors of La0.7Ca0.3Mn0.85Ni0.15O3 below and above TC are well described by an equation of state M(H,e)=eβf±(H/eβ+γ), where e=(T−TC)/TC, f+ for T > TC and f− for T < TC. Having compared to the theoretical models, the critical-exponent values determined in our case are close to those expected for the 3D Ising model and mean-field theory. This indicates an existence of ferromagnetic short-range interactions in the system below TC. The nature of the transformation from first-order to second-order phase tran...
TL;DR: In this article, the magnetic properties of Nd45Fe30Co15Al10 alloy ribbons with various thicknesses of about 120 (N1) and 50 μm (N2) prepared by melt-spinning were studied.
Abstract: We have studied the magnetic properties of Nd45Fe30Co15Al10 alloy ribbons with various thicknesses of about 120 (N1) and 50 μm (N2) prepared by melt-spinning. Structural analyses based on an X-ray diffractometer and a high-resolution transmission electron microscope revealed an existence of nanocrystals with sizes of 10 ~ 20 nm surrounded by an amorphous host matrix. With decreasing ribbon thickness and nanocrystalline size, magnetic studies upon a vibrating sample magnetometer indicated the decrease of the Curie temperature (TC), coercive force (Hc), and magnetic entropy change (ΔSm). In the ferromagnetic region, however, magnetization values determined for N2 are greater than those determined for N1. These results are related to the differences in the critical exponents of N1 (β=0.418 and γ=1.173), and N2 (β=0.512 and γ=1.077), which are characteristic for the ferromagnetic nature existing in the alloy ribbons with different thicknesses.
TL;DR: In this paper, the superparamagnetism behavior and saturation magnetisation of single-phase, nanocrystalline, granular La0.7Ca0.3 (LCMO) samples synthesized by reactive milling method was studied in the temperature range from 200 K to 300 K.
Abstract: In this study, we investigated superparamagnetism behaviour and saturation magnetisation of single–phase, nanocrystalline, granular La0.7Ca0.3MnO3 (LCMO) samples synthesised by reactive milling method. The superparamagnetic behaviour of as–milled samples with various milling times was studied in the temperature range from 200 K to 300 K. The saturation magnetisation of the samples increased from 14.7 to 36.8 emu/g with higher values corresponding to shorter milling time. The observed un–overlapping of the scaled M(Hext, T)/MS versus Hext/T plots and the Curie–Weiss like behaviour of the dc–susceptibility at high temperatures provide evidence that the nanoparticles are interacting superparamagnetic ensembles. The magnetisation curves of interacting nanoparticles were well described by the argument–corrected Langevin function. The saturation magnetisation versus temperature showed a Te dependence with e deviated from 3/2 (value for the Bloch law), which increased with decreasing of the milling time.