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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.

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.

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 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.

The crystal lattice and the bond valence structure of perovskite system La1-xSrxCoO3 are reported. The atomic valences for the given perovskites were determined on the basis of bond-valence theory. For the studied compounds the failure of distortion theorem was observed, and the non-stoichiometry of oxygen was estimated. The model for oxygen distribution is then suggested. The relationship between the grain diameter and oxygen content is discussed. [DOI: 10.1380/ejssnt.2011.469]

Theoretical prediction of magnetism induced by defects or doping in non-metallic colloids has gained a renewed interests recently. In this work, we investigated the possible appearance of magnetism in Cu doped CaO nanocolloids activated by SPAN-80 in the framework of density functional theory (DFT). Despite of strong antiferromagnetic superexchange interaction between Cu$^{2 + }$ ions, the local magnetic moment of Cu may arise due to attachment of colloidal agent onto the surface of CaO nanocluster. The ferromagnetism attributes to the degeneration of Cu 3d orbitals in CaO crystal fields, the aspects of electron correlation and quantum spin fluctuation. %PACS number: 42.30.R, 42.40.Ht, 42.30.Kq

ZnS:Mn nanoparticles were synthesized by co-precipitation method from the precursors solutions of 0.1M Zn(CH\(_{3}\)COO)\(_{2}\), Na\(_{2}\)S and Mn(CH\(_{3}\)COO)\(_{2}\) then were capped with polyvinyl pyrrolidone. The XRD patterns showed that the ZnS:Mn nanoparticles possessed the \(T_d^2 - F4\bar {3}m\) cubic structure with the average crystallite size of several nanometers. At 300~K, the obtained photoluminescence spectra showed only a wide yellow-orange band centered at 603 nm, which should be attributed to the radiation transition of [\(^{4}\)T\(_{1}(^{4}\)G)\( \to ^{6}\)A\(_{1}(^{6}\)S)] of Mn\(^{2 + }\)(3d\(^{5})\) cations in the ZnS matrix. The excitation spectra recorded at 300 K on the other hand featured a strong photoluminescence band around 310-334 nm, which were assigned to the near band-edge absorption transition of ZnS host lattice, in addition with three weaker bands relating to the absorption transitions of [\(^{6}\)A\(_{1}(^{6}\)S) \( \to \) \(^{4}\)T\(_{2}(^{4}\)D)]: 430 nm, [\(^{6}\)A\(_{1}(^{6}\)S) \( \to \) \(^{4}\)A\(_{1}(^{4}\)G) -- \(^{4}\)E(\(^{4}\)G)]: 468 nm, and [\(^{6}\)A\(_{1}(^{6}\)S) \( \to ^{4}\)T\(_{2}(^{4}\)G)]: 498 nm of Mn\(^{2 + }\)(3d\(^{5})\) cations. It was shown that the capping affected only the intensities of emissions bands.

Conference on International Magnetics (INTERMAG), Taipei, TAIWAN, APR 25-29, 2011; International audience; The structure and optical properties of artificial opal thin films, which were synthesized from silica spheres by a modified self-assembly protocol, in the absence and under the applied magnetic field were studied. The surface characterization showed a homogeneous well-ordered face centered cubic structure of silica balls at average size 305 +/- 5 nm. The reflection measurements showed the main reflection plane (1 1 1) besides a minor secondary (2 0 0) plane. The applied field (up to 1000 Oe) induced a systematical splitting of several lines which showed an increase in intensity according to the increase in applied field and thickness of substrate coating MnO(2) layer.

The reaction temperature has essential effect on quality of the product synthesized by hydrothermal method. We report here the variation of the optical characteristics of Mn-doped ZnS nanocrystallites prepared by mean of the stated method from Zn(CH$_{3}$COO)$_{2}$.2H$_{2}$O, Mn(CH$_{3}$COO)$_{2}$.4H$_{2}$O and Na$_{2}$S$_{2}$O$_{3}$.5H$_{2}$O as the precursors. The reaction temperature was set to vary from 120\r{}C to 240\r{}C at a constant reaction time of 15 hours. The XRD patterns showed that, for the reaction temperature range from 120 to 160\r{}C, the obtained products possessed a cubic $T_d^2 - F\overline 4 3m$ and a wurtzite $C_{6v}^4 - P6_3 mc$structure, in which the cubic phase was dominant. At the temperature range from 180 to 240\r{}C, the structures exhibited a cubic phase with the lattice constant increased from 5.41 to 5.43 {\AA}. The photoluminescence spectra showed that with the increase of reaction temperature from 120 to 240\r{}C the intensity of a blue band around 425 - 500 nm (attributed to both Zn, S vacancies) gradually decreased while the intensity of a yellow-orange band at 585 nm (attributed to the $^{4}$T$_{1}(^{4}$G) - $^{6}$A$_{1}(^{6}$S) transition of Mn$^{2 + }$ ions) was enhanced and reached maximum at 220\r{}C. The excitation spectra of the 585 nm band recorded at 160\r{}C showed a band at 335 nm which should be assigned to the near band-edge absorption. With increasing temperature to 200-240\r{}C the new bands appeared at 390, 430, 467, 494 nm. The intensity of these bands increased with temperature and achieved the maxima at 220\r{}C. They should be attributed to the absorption transitions of electrons from ground state $^{6}$A$_{1}(^{6}$S) to excited states$^{ 4}$E($^{4}$D); $^{4}$T$_{2}(^{4}$D); $^{4}$A$_{1}(^{4}$G) - $^{4}$E($^{4}$G); $^{4}$T$_{2}(^{4}$G) of Mn$^{2 + }$(3d$^{5})$ ions, respectively. The bands at 467, 494 nm only exposed clearly in the absorption spectra at 220\r{}C and 240\r{}C.

The bond-valence sum approach to spontaneous valence polarization in perovskite-like nanocrystallites ABO3 is presented. As the bond-valence method allows estimating the amount of valence charge distributed within the given bond according to bond length, the microscopic polarization in the ABO3 structure may be directly derived from the valence deviation in two conjunctive bonding spheres A-O12 and B-O6. The concept was demonstrated on examples and a comparable agreement with data taken either from experiments or first principle calculation was seen. The bond-valence polarization appeared as one of the possible sources contributing to the final macroscopic polarization of the bulk materials.