Search

Abstract: We systematically investigated the various properties of MnTi2O4. The compounds are found to be conducted by small polarons with different activation energies across the temperature T 1 and deviate from the Curie–Weiss law for the magnetic susceptibility at T 1. Also at T 1 do the specific heat undergo a crossover. As indicated by the X-ray diffraction peaks, the series of phenomena near the characteristic temperature T 1 are attributed to the happening of the micro-structural distortion, and the distortion implies the short-range orbital ordering state below T 1. This short-range oribtal ordering state is supported by the little upturn of the thermal conductance at T 1. As the temperature decreases, the systems enter a long-ranged collinear ferrimagnetic state at a lower temperature T N . Moreover, the compounds decreases in thermal-electric power with the decrease of temperature and undergoes a p-type to n-type transition at the temperature T pn . Through the quantitative theoretical analysis, both the decrease of the thermal power and the p-type to n-type transition are cooperatively induced by spin–orbit (SO) coupling and the Jahn–Teller (JT) effect. [Copyright &y& Elsevier]

The magnetic properties of spinel FeCr2S4 single crystals were investigated by ferromagnetic resonance (FMR). The FMR spectrum displays a single absorption line in the whole temperature range measured for both H∥(111) and H⊥(111). With decreasing temperature, the line with H∥(111) shifts to lower fields, while that with H⊥(111) shifts to higher fields. By superposing all the FMR spectra measured in different directions at 110 K, a double-peak is obtained, which clarifies the origin of the FMR double-peak in polycrystalline sample. By taking account of magnetic anisotropy and demagnetizing effect, the orientation dependence of resonance field is well fitted. It is found that the magnetic anisotropy strengthens with decreasing temperature; however, it has no evident influence on transport and colossal magnetoresistance behavior. [Copyright &y& Elsevier]

Abstract: In this paper, the low-field magnetic behavior of polycrystalline FeCr2S4 was investigated by thermal circling the sample from 5 to 200K at a constant magnetic field. We show that, upon cooling the sample at 50Oe to a temperature below the Curie temperature then warming back, the magnetization displays irreversibility between cooling and warming sequence. The irreversible behavior was suppressed gradually with increasing magnetic field. By considering spin-reorientation due to the increase of magnetic anisotropy upon cooling, the irreversible behavior has been explained qualitatively. [Copyright &y& Elsevier]

Here we report a systematic investigation of Co-doping effects on the magnetism and transport properties of Fe 1+ y Te single crystals. It is found that the anti-ferromagnetism transition temperature decreases upon Co doping, and a spin-glass like behavior emerges at low temperature. With substituting more than x =0.09 Co for Fe, both the metallic behavior and the structural transition disappear, but the density of states at Fermi-level does not change significantly. These results suggest that Co doping does not act as carrier doping but is more likely to bring in random magnetic scatters. In addition, the analysis of R H measurements reveals that the Fermi-level reconstruction is not closely related to the long rang AFM transition, which further supports for the local moment picture with frustrated character in dominating the AFM ground state of Fe 1+ y Te. [ABSTRACT FROM AUTHOR]

Highlights: [•] Eu and Gd codoped Y0.9−yEu y Gd0.1BCO thin films were prepared by TFA-MOD. [•] Critical current density was obviously improved by codoping. [•] Flux pinning type was not changed with doping and codoping. [Copyright &y& Elsevier]

Abstract: Y1− x Ho x Ba2Cu3O7− δ (x =0, 0.1, 0.2, 0.3, 0.4, 0.5) thin films were prepared on LaAlO3 (001) substrates by trifluoroacetate metal organic deposition (TFA-MOD) without change of the processing parameters. The highest Jc was attributed to the sample of Y0.6Ho0.4Ba2Cu3O7− δ thin film, whose critical current density is about 1.6 times as compared to that of YBa2Cu3O7− δ thin film at 77K and self field. The flux pinning type was not varied with Ho substitution and can be attributed to δl pinning model, which is attributed to the close ionic radius between the Y3+ and Ho3+ ions. The improvement of Jc by Ho substitution without change of the processing parameters will provide an effective route to enhance the Jc of YBCO-based thin films using TFA-MOD method. [Copyright &y& Elsevier]

Abstract: In this article, ZnO:Cd films were successfully deposited on glass substrates by a sol–gel technique. The influence of doping concentration and annealing temperature effects was carefully investigated. All films exhibited c-axis preferential orientation and optical transparency with visible transmittance >80%. The minimum room temperature resistivity of 0.0341Ωcm was obtained with 10at.% Cd doping under 600°C annealing temperature. The optical band gap of ZnO:Cd film was reduced as Cd doping concentration increased, while the band gap increased with the increase of annealing temperature. [Copyright &y& Elsevier]

Abstract: The structure, magnetic properties, and magnetocaloric effect of La0.7Ca0.3MnO3 ceramics with different particle sizes have been investigated. It is found that the Curie temperature increases first, and then decreases as particle size decreases and the type of magnetic phase transition changes from first-order to second-order, which may be attributed to surface pressure effects. The maximum magnetic entropy change and relative cooling power (RCP) show non-monotonic behaviors with decreasing the particle size. However, for the 3400nm sample, the magnetic entropy change −ΔS M reaches the maximum values of 6.41 and 8.63J/kgK for the field changes of 2.0 and 4.5T, respectively. Furthermore, the estimated large RCP values under lower magnetic fields in La0.7Ca0.3MnO3 are comparable with those of typical magnetic refrigerant materials in the corresponding temperature range, suggesting those compounds might be promising candidates for magnetic refrigeration. [Copyright &y& Elsevier]

Abstract: Critical behavior of Ti-doped La0.7Ca0.3MnO3 ceramics are studied using magnetization methods. The results show that the paramagnetic–ferromagnetic transition is first order for the undoped sample, then for low-doping samples the mean-field model is suitable, and finally a 3D Heisenberg model is satisfied for higher doping samples. These findings demonstrate that the critical behavior of the magnetic transition for manganites is sensitive to Mn-site doping. [Copyright &y& Elsevier]

Abstract: CoFe2O4 ferrite nanoparticles were prepared by a modified chemical coprecipitation route. Structural and magnetic properties were systematically investigated. X-ray diffraction results showed that the sample was in single phase with the space group . The results of field-emission scanning electronic microscopy showed that the grains appeared spherical with diameters ranging from 20 to 30nm. The composition determined by energy-dispersive spectroscopy was stoichiometry of CoFe2O4. The Curie temperature in the process of increasing temperature was slightly higher than that in the process of decreasing temperature. This can be understood by the fact that heating changed Co2+ ion redistribution in tetrahedral and in octahedral sites. The coercivity of the synthesized CoFe2O4 samples was lower than the theoretical values, which could be explained by the mono-domain structure and a transformation from ferrimagnetic to superparamagnetic state. [Copyright &y& Elsevier]