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The saturated magnetization in 20% substituted La0.8R0.2(Fe0.88Si0.12)13 (R = Sm, Tb) magneto-caloric alloys is discussed in this work. The measurements were taken up to 70 kOe (7 Tesla) to detect the saturation of magnetic moments. As reported recently [Mat. Trans. 59(7) (2018) 1068], these compounds show a large variation of magnetic entropies at low field variation (~ 1.5 T), which associate with the large relative cooling efficiency (RCP) of 52 (for Tb-doped) and 102 J/kg (for Sm-doped) even at low effective DH of ~ 15 kOe. We re-detected the effective range of field variation DH and recognized that the effective DH ~ 5 kOe which is much lower than the value of other magneto-caloric compounds and is excellent for application of Sm-doped compound in modern cooling devices. Keywords: Magnetic, alloys, LaFe13, phase transition, rare-earth.

In this work, the perovskite-type oxides LaMO 3 (M = Mn, Fe, Co, Ni) were utilized for sensing electrodes of the electrochemical gas sensors based on the electrolyte YSZ (ZrO 2 + 8%mol Y 2 O 3 ). The sensors with configuration of Pt/YSZ/La M O 3 were sintered at high temperature of 1200 °C in order to analyze influence of the 3 d transition metals ( M ) on gas-sensing characteristics of the perovskite-type oxide electrodes. The sensors were investigated by exposing to various gases of NO 2 , NO, CO, C 3 H 8 and CH 4 . The sensor Pt/YSZ/LaFeO 3 had the best sensitive and selective characteristics to NO 2 gas. The sensors Pt/YSZ/La M O 3 ( M = Mn, Co, Ni) showed poor gas-selectivity. Valence variation of the 3 d transition elements was used to explain the gas-sensing performance of the sensors Pt/YSZ/La M O 3 . The electrical conductance behavior of the oxides La M O 3 was also considered as an important parameter that affected to sensitivity of the sensors Pt/YSZ/La M O 3 , particularly in the high operating temperature.

Low Fe-doped insulating ferromagnets La$_2$CoMnO$_6$ were prepared and studied. The compounds crystallized in orthorhombic space group Pnma with slight changes in the lattice constants. We have observed a significant reduction of resistivity due to doping, together with an increase of magnetization and saturated magnetization as doping level increased. The doping also reduced $T_C$ for both transitions at around 220 and 140 K which attribute for the different spin orderings of the magnetic ions. The small features were also seen at around 40 K and should correspond to the cluster glassy region with spin disorders.

The structure and electrical properties of the thin gold leaves fabricated by Vietnam traditional laminating technology are introduced. The gold leaves are usually created with the average size of 3x3cm, and 200nm thickness, they can easily be broken when handling carelessly. By the measurements of X-ray Diffraction (XRD), and Electron Scanning Microscopy (SEM), the structure and surface morphology were investigated. We have also measured the absorption spectra and determined the resistivity of the samples and found that the gold films possessed the Ca impurities stuck on the surface of the leaves. The conductivity of the films is relatively higher and the absorption maximum is red-shifted in comparison with that of the bulk.

This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of ${\rm La}_{0.7}{\rm Ca}_{0.3}{\rm Mn}_{1-x}{\rm Co}_{x}{\rm O}_{3}(x={0.09}{-}0.17)$ 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 $x\geq 0.11$ 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 $x={\rm 0.17}$ ) exhibit a metal–insulator transition at $T_{P}=60{-}160~{\rm K}$ , 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 . In addition, the conduction data at temperatures $T>\theta_{D}/2$ ( $\theta_{D}$ is the Debye temperature) and $T_{P} 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., $x={\rm 0.10}$ ).

The Mn-doped ZnS nanoparticles with Mn content of 0–15 mol% were synthesized by a hydrothermal method from the solutions Zn(CH3COO)2 0.1 M, Mn(CH3COO)2 0.01 M, and Na2S2O3 0.1 M at 220°C for 15 h. These nanoparticles presented the cubic structure with average particle size about 16 nm. The yellow-orange photoluminescence (PL) band at 586 nm was attributed to the radiation transition of the electrons in 3d5 unfilled shell of Mn2+ ions [4T1(4G)-6A1(6S)] in ZnS matrix. The photoluminescence excitation (PLE) spectra monitored at the yellow-orange band, the absorption spectra also showed the near band edge absorption of 336–349 nm and the characteristic absorption bands of Mn2+(3d5) ions at 392, 430, 463, 468, 492, and 530 nm. These bands should be attributed to the absorption transitions of 3d5 electrons from the ground state 6A1(6S) to the excited states 4E(4D), 4T2(4D), 4A1(4G)-4E(4G), 4T2(4G), and 4T1(4G) of Mn2+ ions. The intensity of PL band and absorption bands of Mn2+(3d5) ions also increased with the Mn content from 0.1 to 9 mol%, but their peak positions were almost unchanged. The PLE spectra showed clearly the energy level splitting of Mn2+ ions in ZnS crystal field and allowed for the calculation of the splitting width between the excited states 4A1(4G), 4E(4G) about of 229 cm−1 (28.6 meV), and the Racah parameters B=559 cm−1, C=3202 cm−1 (γ=C/B=5.7), and the crystal field strength Dq=568 cm−1. The PL spectra with different excitation wavelengths corresponding to absorption transition bands of the PLE spectra allow for the discussion of the indirect and direct excitation mechanisms of Mn2+(3d5) ions in the ZnS crystal.

We report the errors in the evaluation of the surface plasmon resonance of gold nanorods by three classical approaches: the Gans model, the Discrete Dipole Approximation and the Surface Integral method. Using these methods, which are based on the propagation of an electromagnetic wave through a composite medium with different refractive indices, might result in an inaccurate prediction of absorption maxima. For test samples of nanorods prepared by a seed-mediated method, whose homogeneity and quality were also fully demonstrated in this study, the mismatches in the wavelengths of absorption maxima $$ \left| {\varDelta {\lambda_{\max }}} \right| $$ between experimental and theoretical data were observed to be greater than 50 nm. In general, the observed surface plasmon resonances exhibit two distinctive bands corresponding to the transverse and longitudinal modes. The weak transverse mode was located in the region from 510 to 518 nm and varied slightly with the aspect ratio of the rods. In contrast, the longitudinal mode showed a strong dependence on aspect ratio and ranged from 658 to 768 nm. We demonstrated that the mismatches may be sufficiently reduced if the interdependence between these two modes is taken into account.

Electronic structure of a surface-activated PbS by a bio-active molecule 4-aminothiophenol (4-ATP) was investigated using density functional theory (DFT). The obtained results demonstrated the importance of charge transfer which accounted for the flipping of surface rumpling and the nature of the binding between the activated surface and the capping agent. The influence of 4-ATP–PbS topology on bonding nature between surface atoms was discussed. The capping-induced bonding nature shift was interpreted as surface core level shifts (SCLSs) of PbS.

The thermoelectric properties of La-excess alloys of composition La1+δ(Fe0.85Si0.15)13 (δ = 0.06 and 0.09) were studied. As temperature increased from near 0K to room temperature we observed a corresponding increase of electrical resistivity, as a result of continuous metallic behavior of the alloys. On the other hand, the increase of temperature induced an increase of thermal conductivity. The decrease of the thermopower was also observed on increasing temperature and reached the minimum at around the TC then increased again until room temperature.

The Cu–O based spin chain system A2CuO3 (A = Sr, Ca) has attracted considerable attention of scientists during the last decades due to its unique electronic structure. This paper presents a ground state optimization for the periodic structure of Ca2CuO3 using the Density Functional Theory (DFT). The electronic structure analysis was carried out on the basis of cell optimization using the PBE functional with DNP basis set. Until now, the numerical results were obtained only with exclusion of CaO bilayers from full ab initio treatment. We demonstrate here that the correct covalent insulating ground state may be obtained if the antiferromagnetic interaction along the spin chain is included. The best estimated band gap is 0.79 eV. We also show that the CaO bilayers sufficiently contributed to the distribution of d-states above Fermi level.

This paper shows how different lengths, terminations and electronic spin states of one-dimensional chains of Cu–O affected the shieldings in copper nuclear magnetic resonance signals. The calculation was performed for both periodic structure and model clusters of different size and shape. The obtained results showed that there was relatively large splitting of 63Cu resonance for each copper position in the chain.

The spin chain systems with one-dimensional magnetic ordering are promising candidates for quantum optical devices. This paper shows how the optical excitation can induce various phonon modes in an ideal Cu–O chain at various lengths. The calculation was carried out at different level theories including configuration interaction singles for excited states, density functional theory and second-order Moller-Plesset perturbation. In general, the number of modes increases with chain length due to growing asymmetry of atomic positions when chain exceeds 5 nm. There were, however, only two basic modes: one is associated with the symmetric oscillation of oxygen and another with the asymmetric motion of the same along the chain. At the length below 4.3 nm, the Raman activity of the symmetric mode (440 cm −1 ) dominates. From analysis of density of states, this mode may be associated with the excitation across the lowest LUMO bands with changing in spin state.

The authors studied the conduction mechanism in an uranium doped low dimensional magnetic system Ca₂CuO₃. This system exhibits the S=1/2 quasi 1D antiferromagnetic chains of -Cu-O- with strong magnetic coupling, and demonstrates continuous semiconductor-like behavior with constant covalent insulator character. This paper identifies the conduction is due to thermally activated phonon-assisted electron hopping between dopant uranium sites. The parameter a, the characteristic for hopping probability, was determined to be 0.18 A ?1 . This value manifests a relatively stronger hopping probability for Ca₂CuO₃ as compared with other uranium doped ceramics.

We found the large magnetocaloric effect (MCE) in La 0.6 Ca 0.3 Pb 0.1 MnO 3 (sample No. 1), La 0.7 Ca 0.2 Pb 0.1 MnO 3 (sample No. 2), and La 0.7 Ca 0.1 Pb 0.2 MnO 3 (sample No. 3) perovskites, which were prepared by a conventional ceramic method. For a magnetic field change of 13.5 kOe, the magnetic entropy change (Δ S M ) reached values of 2.55, 2.53 and 3.72 J/kg K for samples Nos. 1, 2 and 3, respectively. Interestingly, the large Δ S M was found to occur around 300 K for all samples investigated, which allows magnetic refrigeration at room temperature. These perovskites have the large magnetic entropy changes induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials.