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51.
52.
The problem of instability in polycrystalline ordered double-perovskite Sr2FeMoO6, is presented in this paper. By the X-raydiffraction analysis and the measuring of electrical and magnetic transports, it is indicated that the perovskite structure of thecompound is destroyed, and the Sr2FeMoO6 phase is mainly transformed into SrMo04 phase when the samples are exposedin damp atmosphere for several weeks or immersed in water for several hours. Simultaneously, their electrical and magneticproperties obviously change, and the value of magnetoresistance remarkably reduces and even vanishes at room temperature.A possible micromechanism of the instability and an effective method to avoid the problem of instability are also discussed. 相似文献
53.
石墨化处理对炭/炭复合材料磁电阻特性的影响研究 总被引:8,自引:5,他引:3
对不同温度石墨化处理得到的炭 炭复合材料的磁电阻特性进行了研究。结果表明:1)实验材料出现最大磁电阻的位向均为45° 135°,炭 炭复合材料磁电阻—位向关系不受石墨化处理温度、外磁场强度、测量温度等因素的影响。2)在同一磁场强度情况下,样品磁电阻与测量温度(5K~300K)呈线性关系变化,温度越高磁电阻越低。并且较低石墨化温度处理的样品在一定温度以上磁电阻降低为0,不再变化;2880℃石墨化处理的样品在一定温度以下出现"磁阻饱和值"。3)磁电阻—测量温度曲线回归方程的斜率项随热处理温度的增加而降低,而截距项随热处理温度的增加而增加。4)测量温度相同时,磁电阻随外加磁场强度的增大而增大,在低场(小于1.2T)下,呈现二次函数关系,场强高于1.2T后,磁电阻—磁场强度关系为线性。不同磁场强度下,随石墨化处理温度的提高,磁电阻也增大。 相似文献
54.
Thin films of InAs were deposited on mica substrates by means of controlling both source and substrate temperatures. The temperature
and geometry dependence of the magnetoresistance for these films were investigated. A continuous range of behavior was observed
from films of high electron mobility-low magnetoresistance at one extreme to those of low mobility-high magnetoresistance
at the other. The latter type is shown to be due to excess indium which is occluded during evaporation as a result of the
lower vapor pressure of arsenic. 相似文献
55.
Ralph Rosenbaum Sergiy Balanetskyy Benjamin Grushko Bartosz Przepiórzyński 《Journal of Low Temperature Physics》2008,150(1-2):82-100
Electrical resistivities of two icosahedral (I) Al-Pd-Re alloys have been measured between room temperature and mK temperatures.
One quasicrystalline (QC) polygrain Al-Pd-Re sample exhibited insulating behavior in its resistivities, increasing by a factor of r=R(4 K)/R(300 K)=7.76; its room temperature resistivity was 9,890 μΩ cm. A “phenomenological” expression fitted the conductivity data
well between 300 K to 0.5 K. Below 0.4 K a crossover to an activated variable-range hopping law was observed. Low temperature
magnetoresistance ratio data and fits using the wave function shrinkage theory are presented. A second QC Al-Pd-Re sample
had a small resistance temperature ratio r=2.12. The room temperature resistivity was extremely large, ρ(300 K)≈40,980 μΩ cm. Its conductivity could be described well using a simple temperature power law between 300 K to 20 K.
Below 20 K there was a crossover to a new behavior. Below 1 K, the conductivity could be fitted using a very weakly insulating
power law where σ(T)≈11.37T
0.032 in (Ω cm)−1, suggesting that this sample is located just below the metal-insulator transition. The magnetoconductivity data could not
be fitted successfully using the 3D weak localization (WL) theory and inserting into it physical and realistic fitting magnitudes
for the inelastic magnetic field B
in.
相似文献
56.
Yong-Gang Tang Gui-Ying Wang Guo-Qing Yan Qi-Xiang Song Ming-Yu Zhang Zhen-Sheng Peng 《稀有金属(英文版)》2013,32(1):81-86
Polycrystalline samples of La12x(Sr12yAgy)x MnO3 (y = 0.0, 0.2, 0.4, 0.6, 1.0) were prepared by the solid-state reaction method. The temperature stability of magnetoresistance and magnetoresistance enhancement in La1-x(Sr1-yAgy)x MnO 3 system with both univalent and bivalent elements doped at A site and with unchanged value of Mn3+ /Mn4+ ratio were explored through the measurements of X-ray diffraction patterns, magnetiza-tion-temperature (M-T) curves, resistivity-temperature (q-T) curves and magnetoresistance-temperature (MR-T) curves. The results are as follows: there are two peaks in the q-T curves of the samples with Ag doping, one is caused by resistance change during the paramagnetism-ferromagnetism transition, and the other is from boundary-dependent scattering of conduction electrons on the boundaries of grains. The peak value of MR increases with increasing Ag doping content, and it increases from 8.2 % for y = 0.2 to 29.6 % for y = 1.0 under the magnetic field of B = 0.8 T; MR remains a constant of 12 % in the temperature range of 218-168 K for the sample with y = 1.0, and the temperature stability of MR is in favor of the practical application of MR. 相似文献
57.
Margo Staruch Haiyong Gao Pu‐Xian Gao Menka Jain 《Advanced functional materials》2012,22(17):3591-3595
A nanocomposite film of La0.67Sr0.33MnO3 (LSMO):ZnO is synthesized by depositing LSMO solution on a vertical array of ZnO nanorods grown on (0001) Al2O3 substrate. The magnetic behavior of the composite film differs from that of a pure LSMO film, possibly due to smaller grain size in the composite, small amount of Zn doping, or the presence of nonmagnetic ZnO phase near the LSMO grain boundaries. Magnetotransport measurements show that the low‐field magnetoresistance (LFMR) of the nanocomposite film is significantly enhanced as compared to that observed for pure LSMO film. The highest value of the LFMR of the nanocomposite film at 10 K is –23.9% with a magnetic field of 0.5 T applied parallel to the current. 相似文献
58.
Gang JI ) Ze ZHANG ) Yanxue CHEN ) Shishen YAN ) Yihua LIU ) Liangmo MEI ) ) Institute of Microstructure Properties of Advanced Materials Beijing University of Technology Beijing China ) Institute of Biophysics Chinese Academy of Sciences Beijing China ) School of Physics National Key Laboratory of Crystal Materials Sh ong University Jinan China 《金属学报(英文版)》2009,22(2):153-160
[FeNi(3 nm)/Zn1-xCoxO(3 nm)]2/ZnO(d nm)/[Zn1-xCoxO(3 nm)/Co(3 nm)]2(d=3 and 10) semiconductor junctions were prepared by magnetron sputtering system and photolithography.The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers.The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization αsc in the ZnO layer and the spin injection efficienc... 相似文献
59.
J. Bartlett G. Hardy C. Brockley-Blatt E. Crofts S. Milward M. Brownhill M. Linder 《低温学》2010,50(9):582-590
This paper describes the design, development and performance of the engineering model double adiabatic demagnetization refrigerator (dADR) built and tested under contract to the European Space Agency for its former mission XEUS (now IXO). The dADR operates from a 4 K bath and has a measured recycle and hold time (with a parasitic load of 2.34 μW) at 50 mK of 15 h and 10 h, respectively. It is shown that the performance can be significantly improved by operating from a lower bath temperature and replacing the current heat switches with tungsten magnetoresistive (MR) heat switches, which significantly reduce the parasitic heat load. Performing the latter gives an anticipated recycle and hold time of 2 and 29 h (with a 1 μW applied heat load in addition to the parasitic load), respectively. Such improved performance allows for a reduction in mass of the dADR from 32 kg to 10 kg by operating from a 2.5 K bath (which could be reduced further by optimising the magnet design). Ultimately, continuous operation could be achieved by linking two dADRs to a common detector stage and operating them alternately. Based on this design the mass of the continuous ADR is estimated to be about 4.5 kg. 相似文献
60.
Structure, magnetic and electrical transport properties of the polycrystalline (Fe3O4)100 − xPtx composite films fabricated using DC reactive magnetron sputtering at ambient temperature were investigated systematically. It is found that the films are composed of inverse-spinel-structured polycrystalline Fe3O4 and Pt. Pt addition proves the growth of Fe3O4 grains with the (111) orientation. All the films are ferromagnetic at room temperature. The dominant magnetic reversal mechanism turns from domain wall motion to Stoner-Wohlfarth rotation with the increasing x. The electrical transport mechanism also changes with the increasing x because Pt addition decreases the height of the tunneling barrier at the Fe3O4 grain boundaries, and makes the magnetoresistance of the films decrease. 相似文献