Grain-Size Effect on the Dielectric Properties of La1.5Sr0.5NiO₄ Nano-Particle Materials

Tran Dang Thanh,Le Van Hong,Nguyen Xuan Phuc 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

We have manufactured ceramic samples of La1.5Sr0.5NiO₄and studied their dielectric proper-ties. The samples were prepared by using a reactive mechanical milling technique on D8000-Spex combined with an annealing at a temperature in the range of 700 ℃ - 1000 ℃. The crystalline structure and the sample's purity were checked by means of X-ray diffraction (XRD) on a SIEMENS D5000 spectrograph. The obtained XRD patterns conrmed that all the samples belonged to the F4K2Ni perovskite layer tetragonal structure with a space group of I4/mmm (139). The grain size of a ceramic sample was estimated based on the Field-emission scanning electron microscopy (FE- SEM) images and was calculated by using the Warren-Averbach method based on the Full Width at Half Maximum (FWHM) of the XRD lines. The results obtained by using the two methods were quite the same. The mean grain size (< D >) of the samples varied from 16.2 nm to 95 nm with the annealing temperature. Dielectric constant (ε) of all the samples was estimated from the capacitance measurement at different temperatures in the frequency range of 1 kHz - 13 MHz. The estimated ε of all the samples was about 105 over the whole frequency range up to 1 MHz. The temperature and the frequency dependences of ε(f T), the dielectric constant, were observed and are discussed for all the samples. We have manufactured ceramic samples of La1.5Sr0.5NiO₄and studied their dielectric proper-ties. The samples were prepared by using a reactive mechanical milling technique on D8000-Spex combined with an annealing at a temperature in the range of 700 ℃ - 1000 ℃. The crystalline structure and the sample's purity were checked by means of X-ray diffraction (XRD) on a SIEMENS D5000 spectrograph. The obtained XRD patterns conrmed that all the samples belonged to the F4K2Ni perovskite layer tetragonal structure with a space group of I4/mmm (139). The grain size of a ceramic sample was estimated based on the Field-emission scanning electron microscopy (FE- SEM) images and was calculated by using the Warren-Averbach method based on the Full Width at Half Maximum (FWHM) of the XRD lines. The results obtained by using the two methods were quite the same. The mean grain size (< D >) of the samples varied from 16.2 nm to 95 nm with the annealing temperature. Dielectric constant (ε) of all the samples was estimated from the capacitance measurement at different temperatures in the frequency range of 1 kHz - 13 MHz. The estimated ε of all the samples was about 105 over the whole frequency range up to 1 MHz. The temperature and the frequency dependences of ε(f T), the dielectric constant, were observed and are discussed for all the samples.

Unipolar Resistance Switching Characteristics in a Thick ZnO/Cu/ZnO Multilayer Structure

Tran Le,Hoang Cao Son Tran,Van Hieu Le,Tuan Tran,Cao Vinh Tran,Thanh Tan Vo,Mau Chien Dang,김상섭,이재찬,Bach Thang Phan 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.7

The resistance switching mechanism and the electrical conduction of thick Cu/ZnO/Cu/ZnO/Cu structures were investigated for various ZnO thicknesses (40, 80, 160, and 320 nm) when the thickness of the middle Cu layer was 2 nm. The ZnO films had a microstructure with columnar grains normal to the substrate. The switching voltages (VSET and VRESET) varied with the thickness of the ZnO layer. A symmetric electrode structure exhibited a unipolar resistance switching. The electrical transport of both high-resistance state (HRS) and low-resistance state (LRS) was Ohmic conduction, and the resistance switching mechanism was driven by the formation and the rupture of Cu conducting paths.

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

Unusual Critical Behavior in La_1.2Sr_1.8Mn₂O₇ Single Crystal

Thanh, Tran Dang,Xuan Hau, Kieu,Huyen Yen, Pham Duc,Manh, T. V.,Yu, S. C.,Phan, T. L.,Telegin, A.,Telegin, S.,Naumov, S. IEEE 2018 IEEE transactions on magnetics Vol.54 No.11

<P>In this paper, we present a detailed analysis on the critical behavior of La<SUB>1.2</SUB>Sr<SUB>1.8</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB> single crystal via isothermal magnetization measured at different temperatures around the paramagnetic–ferromagnetic phase transition at <TEX>$T_{C} = 85$</TEX> K. Using the Landau–Lifshitz coefficients, the Arrott plots ( <TEX>$H/M = a(T) + b(T)M^{2}$</TEX>) of sample have been analyzed. It showed that a(T) changed from positive to negative values at different temperatures in the field ranges of <TEX>$H = 0$</TEX>–10, 10–30, and 30–50 kOe, indicating that the critical behavior could not be described with a single model under different applied fields. Through the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, we determined the values of the critical exponents for La<SUB>1.2</SUB>Sr<SUB>1.8</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB> around its magnetic phase transition over different magnetic field ranges. The critical exponent <TEX>$\beta $</TEX> value is found to be 0.501, 0.417, and 0.371 under field ranges of <TEX>$H = 0$</TEX>–10, 10–30, and 30–50 kOe, respectively. This means that the <TEX>$\beta $</TEX> value depends strongly on the strength of the applied field, shifting from the value approaching that of the mean field model ( <TEX>$\beta = 0.5$</TEX>) to the 3-D-Heisenbeg model ( <TEX>$\beta = 0.365$</TEX>). Meanwhile, its <TEX>$\gamma $</TEX> value is quite stable ( <TEX>$\gamma =0.973$</TEX>–1.074), almost independent on the choice of field fitting range. In addition, using the reduced temperature <TEX>$\varepsilon = (T-T_{C}$</TEX>)/ <TEX>$T_{C}$</TEX> and the obtained critical exponents, almost <TEX>$M(H, T$</TEX>) data measured near <TEX>$T_{C}$</TEX> obey the scaling equation <TEX>$M(H, \varepsilon) = \varepsilon ^{\boldsymbol {\beta }}f_{\pm }(H/\varepsilon ^{\boldsymbol {\beta +\gamma }}$</TEX>), where <TEX>$f_{+}$</TEX> and <TEX>$f_{-}$</TEX> are regular analytic functions corresponding to data at <TEX>$T > T_{C}$</TEX> and <TEX>$T < T_{C}$</TEX>, respectively.</P>

AC and DC Conductivity of Multiferroic La2-xSrxNiO4+??

Tran Dang Thanh,Le Van Hong 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5

The DC and AC, up to 1 MHz, conductivity, the thermo-magnetization and the magnetic hysteresis of the La2..xSrxNiO₄+δ polycrystalline ceramic were measured and estimated over a wide temperature range from 20 K to 300 K. The obtained results show that La2..xSrxNiO₄+δ is multiferroic. In the DC region measurement the samples exhibit a semiconductor-like behavior with the activation energy decreasing with increasing Sr concentration. Clear evidence of charge ordering and spin ordering are observed around temperatures of 75 K and 200 K in samples doped with Sr at concentrations below 15 % (x < 0:3). The AC conductivity exhibits a change in conducting behavior at a peak temperature, Tp, near Tco and depends on frequency, which should be related to a change in the stripe structure of the nickelate, as well as to the multiferroic behavior of this material. The DC and AC, up to 1 MHz, conductivity, the thermo-magnetization and the magnetic hysteresis of the La2..xSrxNiO₄+δ polycrystalline ceramic were measured and estimated over a wide temperature range from 20 K to 300 K. The obtained results show that La2..xSrxNiO₄+δ is multiferroic. In the DC region measurement the samples exhibit a semiconductor-like behavior with the activation energy decreasing with increasing Sr concentration. Clear evidence of charge ordering and spin ordering are observed around temperatures of 75 K and 200 K in samples doped with Sr at concentrations below 15 % (x < 0:3). The AC conductivity exhibits a change in conducting behavior at a peak temperature, Tp, near Tco and depends on frequency, which should be related to a change in the stripe structure of the nickelate, as well as to the multiferroic behavior of this material.

Electrical and Magnetotransport Properties of <inline-formula> <tex-math notation='TeX'> <tex> ${\rm La}_{{0.7}}{\rm Ca}_{{0.3}}{\rm Mn}_{{1-x}}{\rm Co}_{{x}}{\rm O}_{3}$ </tex> </tex-math></inline-formula>

Tran Dang Thanh,Phan, T. L.,Phung Quoc Thanh,Hoang Nam Nhat,Duong Anh Tuan,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.6

<P>This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of La0.7Ca0.3Mn1-xCoxO3(x = 0.09-0.17) prepared by solid-state reaction. Magnetic measurements versus temperature revealed a gradual decrease of the magnetization (M) and Curie temperature (T-C) with increasing Co concentration (x). The T-C values vary from 194 to 159 K as changing x from 0.09 to 0.17, respectively. H/M versus M-2 performances around T-C prove the x = 0.09 sample undergoing a first-order magnetic phase transition (FOMT) while the samples with x >= 0.11 undergo a second-order magnetic phase transition (SOMT). The other with x = 0.10 is considered as a threshold concentration of the FOMT-SOMT transformation. Considering temperature dependences of resistivity, rho(T), in the presence and absence of the magnetic field, the samples (excepting for x = 0.17) exhibit a metal-insulator transition at T (P) = 60-160 K, which shifts toward lower temperatures with increasing x. In the metallic-ferromagnetic region, the rho(T) data are well fitted to a power function rho(T) = rho(0) + rho(2) T-2 + rho(4.5) T-4.5. This indicates electron-electron and electron-magnon scattering processes are dominant at temperatures T < T (P). In addition, the conduction data at temperatures T > theta(D)/2 (theta(D) is the Debye temperature) and T (P) < T < theta(D)/2 obey the small-polaron and variable-range hopping models, respectively. The values of activation energy E-p, and density of states at the Fermi level N(E-F) were accordingly determined. Here, N(E-F) increases while E-p decreases when an external magnetic field is applied. We also have found that N(E-F) increases when materials transfer from the FOMT to the SOMT, and N(E-F) value becomes smallest for the sample having the coexistence of the FOMT and SOMT (i.e., x = 0.10).</P>

Critical behavior of the ferromagnetic-paramagnetic phase transition in Fe_90−xNi_xZr₁₀ alloy ribbons

Thanh, Tran Dang,Huy Dan, Nguyen,Phan, The-Long,Kumarakuru, Haridas,Olivier, Ezra J.,Neethling, Johannes H.,Yu, Seong-Cho American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.115 No.2

Influence of Mn Doping on the Crystal Structure, and Optical and Magnetic Properties of <inline-formula> <tex-math notation='TeX'> <tex> ${\rm SrTiO}_{3}$ </tex> </tex-math></inline-formula> Compounds

Tran Dang Thanh,Phan, T. L.,Le Mai Oanh,Nguyen Van Minh,Jong Suk Lee,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.6

<P>This paper presents the influence of Mn doping on the structural characterization, and optical and magnetic properties of SrTi<SUB>1-x</SUB>Mn<SUB>x</SUB>O<SUB>3</SUB>(x = 0.0-0.1) materials prepared by a solid-state reaction method. The detailed analyses of X-ray diffraction patterns indicate an incorporation of Mn dopants into Ti sites of the SrTiO<SUB>3</SUB> host lattice. There is a cubic to tetragonal transformation, which takes place at a threshold concentration x ≈ 0.04. The optical absorption spectra show a rapid increase in the absorption coefficient. The bandgap energy (Eg) related to the direct electron transition decreases with increasing Mn concentration: Eg decreases from 3.15 eV for x = 0 to 1.28 eV for x = 0.10. From this point of view, the SrTi<SUB>1-x</SUB>Mn<SUB>x</SUB>O<SUB>3</SUB> materials are considered as promising materials for photocatalytic applications. Interestingly, while the samples with x = 0.0-0.02 are diamagnetic, the others with x = 0.04-0.10 exhibit weak ferromagnetism. The ferromagnetic order increases with increasing Mn concentration. Based on the results of structural and optical analyses, the nature of magnetism in the samples is explained thoroughly.</P>

Dielectric resonance effect with negative permittivity in a La1.5Sr0.5NiO4+δ ceramic

Tran Dang Thanh,Nguyen Van Dang,Le Van Hong,The-Long Phan,Seong-Cho Yu 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10

A polycrystalline sample of La1.5Sr0.5NiO4+δ was prepared by using a solid-state reaction. Xraydiffraction proved the sample to be a single phase with a tetragonal structure (space group:I4/mmm). By using an iodometric titration method to determine the non-stoichiometric oxygenconcentration (δ) in La1.5Sr0.5NiO4+δ, we found δ = −0.017, which corresponds to a doping level ofnh = x + 2δ = 0.466. Also, a strong increase of the magnetization in theM(T) curve at temperaturesbelow the spin-ordering temperature (TSO 100 K) was observed. The M(H) curves show verysmall magnetic moments, which proves the weak ferromagnetic nature of La1.5Sr0.5NiO4+δ. Thedependences of the dielectric constant on the frequency and the temperature, "(!, T) = "0(!, T) +i"00(!, T), was investigated in the frequency range of 1 − 13 MHz. At temperatures around roomtemperature, the maximum of the real part ("0) was higher than 105. Particularly, an abnormaldependence of the permittivity on frequency was observed. Depending on temperature, a dielectricresonance was observed at about 500 kHz or 8 MHz. Interestingly, we observed the dielectricresonanceeffect with a negative permittivity. Such a feature is very similar to that observed inleft-handed materials. The fitting of the experimental data for the dielectric constant at frequenciesaround the resonance frequency to the equations associated with an equivalent RLC series circuitproves that La1.5Sr0.5NiO4+δ belongs to the class of multiferroic materials.

Coexistence of short- and long-range ferromagnetic order in La_0.7Sr_0.3Mn_1−xCo_xO₃ compounds

Thanh, Tran Dang,Linh, Dinh Chi,Manh, T. V.,Ho, T. A.,Phan, The-Long,Yu, S. C. American Institute of Physics 2015 Journal of Applied Physics Vol.117 No.17