Journal of Physics D-Applied Physics
A large magnetoresistance (MR) is observed in a double helical CoMnSi compound over the entire temperature region from 5 K to the maximum measuring temperature of 380 K, with the largest MR ratio of -18.3% at 245 K and the smallest MR ratio of -5.5% at 85 K at 5 T. This phenomenon is ascribed to two different mechanisms in different temperature regions. The suppressed spin fluctuations of the double helical structure are responsible for the MR below 110 K. However, in consideration of the natural multilayer superstructure of CoMnSi, the larger MR above 110 K is ascribed to the decrease in K-space restrictions when the change in magnetic structure from double helical order to fan order occurs.
关键词:
giant magnetoresistance;magnetic-structure;crystal;metals
Journal of Physical Chemistry C
alpha-K(x)MnO(2) nanotubes with x = 0.10, 0.12, 0.15, and 0.17 have been synthesized through acid and alkali treatments of the precursor alpha-MnO(2) nanotubes. For the samples with x = 0.10 and 0.12, a large divergence of the ZFC and FC susceptibilities and pronounced hysteresis at low temperature are observed. However, the samples with x = 0.15 and 0.17 are antiferromagnetic with Neel temperatures of 25.4 and 25.3 K, respectively. The reciprocal susceptibility and electrical conductivity indicate that the samples with x = 0.15 and 0.17 undergo a charge separation transition from mixed/averaged valence state manganese ions to Mn(3+) and Mn(4+) between 250 and 300 K. Below half occupancy of the K(+) site (x <= 0.125), the strong geometrical frustration due to the triangular lattice configuration and the mixture of Mn(3+)/Mn(4+) result in the spin-glass behavior of the samples with x = 0.10 and 0.12. Above half occupancy of the K(+) site, the samples with x = 0.15 and 0.17 exhibit an antiferromagnetic feature due to the charge separation of Mn(3+) and Mn(4+). Our experiments display that the magnetic properties of alpha-K(x)MnO(2) can be tuned by varying the K(+) content.
关键词:
hydrothermal synthesis;manganese-dioxide;hollow urchins;tunnel;phase;transitions;nanowires;growth;oxides
李丽荣
,
赵娟
,
王贵
金属功能材料
采用非晶态多核配合的方法在800℃制备出La0.85K0.15MnO3纳米颗粒,用XRD、HRTEM和PPMS等手段对纳米颗粒的微观结构和磁性能进行研究.XRD和ED分析表明,所有样品都具有单相钙钛矿结构;样品的M-丁曲线研究结果表明,La0.85K0.15MnO3纳米颗粒的居里温度Tc为242.65 K.
关键词:
居里温度
,
纳米颗粒
,
La0.85K0.15MnO3
Oxidation of Metals
The corrosion of four Fe-Cr commercial steels with different tents in a simulated waste-gasification atmosphere containing 0.5 vol.% H-2, 0.5 vol.% HCl, balance CO2 has been investigated at 773 and 873 K. The same materials have also been tested in the same gas mixture free from HCl at both temperatures for comparison. The results show that the materials with low-chromium content (2.25 CrMoV and NF616) undergo accelerated corrosion in the presence of HCl, while the stainless steel SS304 suffers very little corrosion. On the contrary a steel containing 12 wt.% Cr (12 CrMoV) corrodes rather rapidly at 773 K but quite slowly at 873 K. The beneficial effect of chromium on the corrosion resistance of the steels increases with the chromium content at both temperatures. The steels tested show corrosion rates generally decreasing with time, having kinetics which are approximately parabolic at 773 K but intermediate between parabolic and linear at 873 K Only little or even no chlorine can be detected at the scale/metal interface at both temperatures for all materials corroded in HO-containing atmospheres. The corrosion mechanism can be explained by the so-called "active-oxidation, model.
关键词:
Cr steels HCl;reducing atmosphere;corrosion;high-temperature corrosion;fe-cr alloys;hydrogen-chloride;chromium-alloys;gas-mixtures;oxygen;800-degrees-c;oxidation;metals;fuels
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
Nanoscale Research Letters
The linear thermal expansions (LTE) of bulk nanocrystalline ingot iron (BNII) at six directions on rolling plane and conventional polycrystalline ingot iron (CPII) at one direction were measured from liquid nitrogen temperature to 300 K. Although the volume fraction of grain boundary and residual strain of BNII are larger than those of CPII, LTE of BNII at the six measurement directions were less than those of CPII. This phenomenon could be explained with Morse potential function and the crystalline structure of metals. Our LTE results ruled out that the grain boundary and residual strain of BNII did much contribution to its thermal expansion. The higher interaction potential energy of atoms, the less partial derivative of interaction potential energy with respect to temperature T and the porosity free at the grain boundary of BNII resulted in less LTE in comparison with CPII from liquid nitrogen temperature to 300 K. The higher LTE of many bulk nanocrystalline materials resulted from the porosity at their grain boundaries. However, many authors attributed the higher LTE of many nanocrystalline metal materials to their higher volume fraction of grain boundaries.
关键词:
Linear thermal expansion;Bulk nanocrystallined materials;Severe;rolling technique;electrochemical corrosion behavior;different grain sizes;microstructure;diffraction;selenium;metals
荀玉强
,
杨鲁伟
,
蔡京辉
,
梁惊涛
,
周远
工程热物理学报
介绍了一套实用型单级高频同轴脉冲制冷机工作在深低温区的性能特性.输入功率为200 W时,冷头无负荷最低温度可达到29.35 K,输入功率为235 W时,冷头无负荷温度可稳定在28.55 K.这是目前国内无多路旁通的单级高频脉冲管制冷机获得的最低温度,国际上位于先进行列.200 W输入条件下,35.6 K可提供0.5 W制冷量,为30～40K温区相关的小冷量应用提供了一种简单有效的方法.
关键词:
脉冲管制冷机
,
高频
,
单级
,
同轴
,
双向
Ying LI
材料科学技术（英文）
Oxide materials NaCo2O4 and (Na1-yMy)1.6Co2O4 (M=K, 0.05≤y≤0.35; M=Ca, Sr, 0.10≤y≤0.40) were prepared by a sol-gel method. Experimental results indicated that the Seebeck coefficient and the Power-factor of Na Co2O4 were improved by doping Ca and Sr but not by K. The Power-factor of NaCo2O4 is in its maximum, 1.68×10-4 W•m-1•K-2 and 11% bigger than that of the original one when the dopant fraction of Ca was 0.1. Doping Sr makes NaCo2O4 have the biggest Power-factor, 1.68×10-4 W•m-1•K-2 that is 50% bigger than the non-doping oxide. The experimental results indicate that suitable dopants and addition amounts could improve the thermoelectric properties of NaCo2O4 greatly.
关键词:
Thermoelectric materials
,
materials
,
Electric
,
proper
