共查询到19条相似文献,搜索用时 109 毫秒
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宽温区磁致冷机工质材料的优化 总被引:2,自引:0,他引:2
评述了在室温以下的整个低温温区磁致冷机工质材料的研究进展,其中包括为扩展有效致冷温区而设计的复合铁磁材料,新近发展迅速的纳米磁致冷材料,在H2液化器中适用的稀土金属间化合物,以及纯4f族合金等。评价了各种工质材料的性能,通过对磁致冷H2液化器的Yong分析,给出了工质材料的优化判据。 相似文献
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文章介绍了2004年度国家自然科学二等奖获奖成果[21].类钙钛矿型材料是一类物理内涵极其丰富的化合物,它是著名的高温超导材料、铁电材料、压电材料,又是庞磁电阻效应材料,目前又显示出具有大磁熵变效应与隧道磁电阻效应.文章作者系统地研究了锰钙钛矿磁性化合物的磁熵变与组成、微结构以及颗粒尺寸的关系,研究结果表明,磁性钙钛矿化合物具有显著的磁熵变,居里温度易调,并且化学稳定性佳,从而成为一类新型的磁制冷工质候选材料.此外,文章作者还研究了钙钛矿化合物纳米颗粒体系的磁电阻效应,发现除人们发现的居里温度附近的本征的庞磁电阻效应外,在很宽的低温区,存在与温度不甚敏感的隧道磁电阻效应. 相似文献
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生物磁技术在食用菌栽培中的应用 总被引:2,自引:0,他引:2
用磁场处理水(简称磁水,下同)喷浇食用菌能获得高产,这是生物磁技术在食用菌栽培中应用的新成果,实验表明:用磁不拌料加菇期喷浇磁水的方法最好,它可使食用菌增产10%-50%,磁水能使纤维素酶,脂酶,淀粉酶等酶的活性增加,加速了纤维素,脂肪,淀粉等养分的分解,并提高这些养分的利用率,达到增产的效果,这是食用菌喷施磁水获得增产的重要原因。 相似文献
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磁制冷技术的发展取决于具有大磁热效应磁制冷材料的研发进展.经过长期的工作积累,特别是近20年来的努力,许多新型磁制冷材料的探索和研究极大地促进了磁制冷技术的进步.本文介绍了磁热效应的基本原理和磁制冷研究的发展历史,系统综述了低温区和室温区具有大磁热效应的磁制冷材料的研究进展,重点介绍了一些受到较为关注的磁热效应材料的最新研究成果.低温区磁制冷材料主要包括具有低温相变的二元稀土基金属间化合物(RGa,RNi,RZn,RSi,R_3Co以及R_(12)Co_7)、稀土-过渡金属-主族金属三元化合物(RTSi,RTAl,RT_2Si_2,RCo_2B_2,RCo_3B_2)以及四元化合物RT_2B_2C等,其中R代表稀土元素,T代表过渡金属.这些材料一般都具有二级相变,具有良好的热、磁可逆性,也因其合金属性具有良好的导热性.室温区磁制冷材料主要包括Gd-Si-Ge,La-Fe-Si,Mn As基,Mn基Husler合金,Mn基反钙钛矿,Mn-Co-Ge,Fe-Rh以及钙钛矿氧化物等系列.这些材料一般都具有一级相变,多数在室温具有巨大的磁热效应而受到国内外的极大关注.其中,La-Fe-Si系列是国际上普遍认为具有重要应用前景的磁制冷工质之一,也是我国具有自主知识产权的材料.本文还对磁制冷材料的发展方向进行了展望. 相似文献
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We report on the magnetic properties and magnetocaloric effects of Mn_5Ge_{3-x}Ga_x compounds with x=0.1, 0.2, 0.3, 0.4, 0.6 and 0.9. All samples crystallize in the hexagonal Mn_5Si_3-type structure with space group P6_3/mcm and order ferromagnetically. The Curie temperature of these compounds decreases with increasing x, from 306K (x=0.1) to 274K (x=0.9). The average Mn magnetic moments increases with increasing Ga content, reaching a maximum value at x=0.6. The magnetic entropy changes in these compounds are determined from the temperature and field dependence of the magnetization using the thermodynamic Maxwell relation. The Ga substitution has two kinds of influence on the magnetocaloric effect (MCE) of Mn_5Ge_3. One is that the magnitude of the magnetic entropy change decreases, the other is that the MCE peak becomes broadened. 相似文献
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Effect of Co substitution on magnetic properties and magnetic entropy changes in LaFe11.83Si0.94Al0.23 compounds 下载免费PDF全文
Effect of Co substitution on magnetic properties and magnetic entropy changes in LaFe_{11.83}Si_{0.94}Al_{0.23} compounds has been investigated by means of magnetization measurements. X-ray diffraction shows the prepared compounds to be single phase with the cubic NaZn_{13}-type structure. Substitution of Co for Fe leads to an increase of Curie temperature of the material. The magnetic entropy changes in LaFe_{11.83}Si_{0.94}Al_{0.23} and LaFe_{11.03}Co_{0.80}Si_{0.94}Al_{0.23} compounds are 21.8J/(kg·K) to 16.9J/(kg·K) under a magnetic field change of 0-5T at Curie temperature, respectively. Giant magnetic entropy changes are attributed to the higher magnetization and the rapid change in magnetization at Curie temperature. 相似文献
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The magnetic properties and magnetocaloric effects in binary R-T(R = Pr,Gd,Tb,Dy,Ho,Er,Tm;T = Ga,Ni,Co,Cu)intermetallic compounds 下载免费PDF全文
In this paper, we review the magnetic properties and magnetocaloric effects(MCE) of binary R–T(R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series, R_(12)Co_7 series, R_3 Co series and RCu_2series), which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin(S) and atoms with large total angular momentum(J) are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change(?SM), refrigerant temperature width(Twidth)or refrigerant capacity(RC) is enlarged for some R–T compounds. In the low temperature range, binary R–T(R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series,R_(12)Co_7 series, R_3 Co series and RCu_2series) show excellent performance of MCE, indicating the potential application for gas liquefaction in the future. 相似文献
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Large magnetic entropy change and magnetic properties in La (Fel-xMnx)ll.TSil.3Hy compounds 下载免费PDF全文
Magnetic properties and magnetic entropy change in La(Fe_{1-x}Mn_x)_{11.7}Si_{1.3}H_y compounds have been investigated. A significant increase of the Curie temperature T_C and a small increase of the saturation magnetizations μ_S have been observed after the introduction of interstitial H, which caused a slight volume expansion. The first-order field-induced itinerant-electron metamagnetic (IEM) transition remains and brings about a large magnetic entropy change around room temperatures for the compounds. The maximal magnetic entropy change is about 23.4, 17.7 and 15.9J/kg·K under a magnetic field change from 0 to 5T for x=0.01, 0.02 and 0.03, respectively. Therefore, the compounds appear to be potential candidates for magnetic refrigerants around room temperatures. 相似文献
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Magnetic properties and magnetoresistance of HfFe2Ge2-type Dy1-xGdxMn6Ge6 (x=0.1-0.6) compounds 下载免费PDF全文
The magnetic properties and magnetoresistance effects of Dy_{1-x}Gd_xMn_6Ge_6 (x=0.1-0.6) compounds have been studied by magnetic properties and resistivity measurements in applied magnetic fields up to 5T. The compounds with x=0.1, 0.2, 0.4 and 0.5 order antiferromagnetically at 425, 428, 430 and 432K, respectively, and there are second magnetic phase transitions below 100K. The compound with x=0.6 exhibits a transition from ferrimagnetic to antiferromagnetic, then to ferrimagnetic state again with decreasing temperature. Furthermore, it displays a field-induced metamagnetic transition, and its threshold field decreases with increasing temperature. The magnetoresistance curve of the compound with x=0.6 in applied magnetic fields up to 5T is presented and the magnetoresistance effects are related to the metamagnetic transitions. 相似文献
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研究了Mn5Ge2.7M0.3(M=Ga,Al,Sn)化合物的磁性和磁熵变. x射线衍射实验表明,研究的化合物均呈六角Mn5Si3型结构. 三种原子对Ge原子的替代,使得平均Mn原子磁矩下降,但居里温度没有明显的变化. 由于磁矩的降低,导致磁熵变值的下降,在磁场变化为4.0×106A·m-1时,对应于M=Ga,Al和Sn的样品,最大磁熵变值ΔSmaxM分别为6.1,6.3和5.3J·kg-1K-1,但磁熵变峰值的半高宽ΔTFWHM有所增加. 另外,Mn5Ge2.7M0.3(M=Ga,Al,Sn)化合物在高于居里温度的Arrott曲线上出现了一个不连续点,即样品在一定温度下的顺磁磁化率在某一临界磁场下发生了突变,临界磁场与温度几乎呈正比关系.这可能是由于样品在加一定磁场时3d带的费米能级发生了变化,使得有效电子数的减少所致.
关键词:
居里温度
平均Mn原子磁矩
磁熵变
Arrott图 相似文献
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Effects of Fe-Fe bond length change in NaZn13-type intermetallic compounds on magnetic properties and magnetic entropy change 下载免费PDF全文
In this paper the effects of Fe-Fe bond length change on magnetic properties and magnetic entropy change have been investigated on LaFe_{12.4-x}Si_xCo_{0.6} and LaFe_{12.3-x}Al_xCo_{0.7} intermetallic compounds. According to the analyses of Fe-Fe bond length change, the variation of Curie temperature and the unusual magnetic phase transition which results in the large magnetic entropy change were explained. The effects of the substitution of Co and Si for Fe on magnetic entropy change and field-induced itinerant-electron metamagnetic transition in LaFe_{12.4-x}Si_xCo_{0.6} compounds were also studied and the considerable magnetic entropy change has been achieved. 相似文献
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Magnetism and magnetic entropy changes in LaFe11A12Cx(x=0.0, 0.2 and 0.5) compounds have been investigated.The Curie temperature TC is conveniently controlled from 200K to room temperature by varying the carbon concentration.Large magnetic entropy change is obtained over a wide temperature range due to the high magnetization and the drastic decrease in the magnetization around TC.The large magnetic entropy change in wide temperature range,low cost and the convenience of controlling TC suggest that the LaFe11Al2Cx compounds are promising candidates for magnetic refrigerants in the corresponding temperature range. 相似文献