Magnetocaloric Effect in Sr0.4Ba1.6−x La x FeMoO6

Magnetocaloric effect in half-metallic double perovskite Sr_0.4Ba_1.6?x La _x FeMoO₆ (x = 0, 0.1, 0.2, 0.3) were investigated. It is shown that Sr_0.4Ba_1.6?x La _x FeMoO₆ exhibits the largest magnetic entropy change (ΔS _M ) of 0.086 J/kg K upon 0.2 T magnetic field variation. Furthermore, ΔS _M distribution of the Sr_0.4Ba_1.6?x La _x FeMoO₆ is much more uniform than that of gadolinium. Through these results, polycrystalline samples of Sr_0.4Ba_1.6?x La _x FeMoO₆ have some potential applications for magnetic refrigerants in a wide temperature range, including room temperature.     

La0.67-xCa0.33MnO3系列样品的磁热效应

用溶胶-凝胶法制备了不同空位浓度掺杂的La0.67-xCa0.33MnO3系列样品(x=0.00,0.02,0.06,0.10),用扫描电子显微镜(SEM)观察了样品的形态和颗粒大小,X射线衍射实验结果显示样品为单相钙钛矿结构,用振动样品磁强计(VSM)测量了样品的磁化强度随温度变化的M-T曲线和起始磁化M-H曲线.研究了空位浓度对样品的居里温度Tc和磁熵变的影响.结果表明,空位浓度的掺杂将样品的居里温度Tc提高至室温附近,磁熵变得到增强.对于经历了一级相变的样品La0.67-xCa0 33MnO3(x=0.02),在居里温度Tc(277 K)附近和1T外磁场下,最大磁熵变达到了2.78 J/(kg·K).     

Low Magnetic Field Magnetocaloric Effect in $\text {Gd}_{\mathrm {5-}_{x}}$EuxGe4

The magnetocaloric effect is investigated for \(\text {Gd}_{\mathrm {5-}_{x}}\)Eu _x Ge₄ (0.25 ≤ x ≤ 2) system near a phase transition from a ferromagnetic to a paramagnetic state as a function of temperature with low external magnetic field change of 100 Oe. The sample with x = 1 has the smallest value of maximum magnetic entropy change and the specific heat change, and highest values of full-width at half-maximum and relative cooling power. The results indicate that the \(\text {Gd}_{\mathrm {5-}_{x}}\)Eu _x Ge₄ system has a prospective application for magnetic refrigerant in an extended high temperature range. Consequently, \(\text {Gd}_{\mathrm {5-}_{x}}\)Eu _x Ge₄ compounds are very attractive candidates for magnetic refrigeration applications, especially nitrogen liquefier.     

Tb掺杂双钙钛矿氧化物Pr2CoMnO6的磁热效应

采用高温固相反应法制备双钙钛矿氧化物Pr_(2-x)Tb_xCoMnO₆(x=0,0.05,0.1,0.15)系列陶瓷样品,研究了Tb的掺杂量对Pr₂CoMnO₆样品的居里温度、磁熵变以及磁相变的影响。结果表明:系列样品Pr_(2-x)Tb_xCoMnO₆(x=0,0.05,0.1,0.15)的空间点群为单斜晶系P2₁/n,具有良好的单相性;该组样品均有两个磁转变点(T_C1和T_C2);随着Tb掺杂量的增加T_C1和T_C2均降低下降;在测量温区内,随着温度的降低4个样品均先后经历顺磁态、顺磁-铁磁共存态;该组样品在7 T外加磁场中的最大磁熵变值ΔS_M分别为-1.862、-1.779、-1.768和-1.766 J/(kg·K)。掺杂Tb元素使最大磁熵变值变小,但是拓宽了半高宽温区。结合RCP值可以判断,Pr_1.9Tb_0.1CoMnO₆比其他三个样品更具有作为高温区磁制冷材料的潜能;根据对Arrott曲线、重标定曲线以及Loop曲线的分析,该组样品在此阶段经历了一级相变。     

Templated synthesis and characterization of red-emitting $$\hbox {Ca}_{{1-x}}\hbox {Sr}_{1-x}\hbox {Eu}_{2x}^{3+}\hbox {SiO}_{4}$$ phosphor for LED applications

A novel attempt towards the synthesis of red-emitting europium (\(\hbox {Eu}^{3+}\))-doped \(\hbox {CaSrSiO}_{4}\) phosphors has been made through a templated strategy using non-ionic surfactant as template. The concentrations of \(\hbox {Eu}^{3+}\) in the host were altered and the optimized concentration to extract the maximum efficacy was analysed. The crystalline structure and morphologies of the synthesized phosphor were studied and analysed. The results show the aggregated rod-like morphology with a continuous porous network that shows the maximum intensity at 10 mol% of dopant.     

Evidence for One-Gap Superconductivity in Mg(B_{1-x}C_{x})_{2} Single Crystals at x=0.132 by Point-Contact Spectroscopy

We report the results of directional point-contact measurements in Mg(B $_{1-x}$ C $_{x})_{2}$ single crystals. The amplitudes of the gaps, $\Delta_{\pi}$ and $\Delta_{\sigma}$ , were determined for each C content by fitting the experimental low-temperature normalized conductance curves of our “soft” point contacts with the BTK model generalized to the two-band case. We found that, on increasing the carbon content, $\Delta_{\sigma}$ decreases almost linearly with $T_{c}$ and $\Delta_{\pi}$ slightly increases until, at $x=0.132$ (where $T_{c}=19$ K), they assume the same value $\Delta =3.2 \pm 0.9$ meV. This result is confirmed by the temperature and magnetic-field dependence of the conductance curves at this C content, which do not show any evidence of two distinct gap values. In particular, the Δ versus T curve follows very well a standard BCS curve, with a gap ratio $2\Delta /k_{B} T_{c}=3.9$ . These experimental findings are compared to the theoretical predictions of the two-band model in the Eliashberg formulation.     

Caustic Pattern of Magnetoelastic Waves in the Vicinity of Magnetoelastic Resonance in Fe $$_{1-x}$$ 1 - x Ga $$_{x}$$ x Crystal

Journal of Superconductivity and Novel Magnetism - The vicinities of two resonance points where longitudinal and transverse elastic waves interact with the magnetic mode are considered. The caustic...     

Synthesis,structure and thermoelectric properties of $$\mathrm{La}_{1-x}\mathrm{Na}_{x}\mathrm{CoO}_{3 }$$ perovskite oxides

Monovalent ion doped lanthanum cobaltate \(\hbox {La}_{1-x}\hbox {Na}_{x}\hbox {CoO}_{3 }\) (\(0 \le x \le 0.25\)) compositions were synthesized by the nitrate–citrate gel combustion method. All the heat treatments were limited to below 1123 K, in order to retain the Na stoichiometry. Structural parameters for all the compounds were confirmed by the Rietveld refinement method using powder X-ray diffraction (XRD) data and exhibit the rhombhohedral crystal structure with space group R-3c (No. 167). The scanning electron microscopy study reveals that the particles are spherical in shape and sizes, in the range of 0.2–0.5 \(\upmu \)m. High temperature electrical resistivity, Seebeck coefficient and thermal conductivity measurements were performed on the high density hot pressed pellets in the temperature range of 300–800 K, which exhibit p-type conductivity of pristine and doped compositions. The X-ray photoelectron spectroscopy (XPS) studies confirm the monotonous increase in \(\hbox {Co}^{4+}\) with doping concentration up to \(x = 0.15\), which is correlated with the electrical resistivity and Seebeck coefficient values of the samples. The highest power factor of \(10~\upmu \hbox {W~mK}^{-2 }\) is achieved for 10 at% Na content at 600 K. Thermoelectric figure of merit is estimated to be \({\sim }1 \times 10^{-2}\) at 780 K for 15 at% Na-doped samples.