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Large magnetic entropy change near room temperature in the LaFe11.5Si1.5H1.3 interstitial compound 总被引:2,自引:0,他引:2 下载免费PDF全文
The LaFe11.5Si1.5H1.3 interstitial compound has been prepared. Its Curie temperature TC (288 K) has been adjusted to around room temperature, and the maximal magnetic entropy change (|ΔS|~17.0 J·kg-1·K-1 at TC) is larger than that of Gd (|ΔS|~9.8 J·kg-1·K-1 at TC=293 K) by ~73.5% under a magnetic change from 0 to 5 T. The origin of the large magnetic entropy change is attributed to the first-order field-induced itinerant-electron metamagnetic transition. Moreover, the magnetic hysteresis of LaFe11.5Si1.5H1.3 under the increase and decrease of the field is very small, which is favourable to magnetic refrigeration application. The present study suggests that the LaFe11.5Si1.5H1.3 compound is a promising candidate as a room-temperature magnetic refrigerant. 相似文献
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该主要研究了高温超导体在脉冲磁场中的磁热稳定性,与传统低温超导体相比,HTS所不同的是最不稳定的状态发生在磁通跳跃区,理论上借助E-j曲线和有限热扩散方程推导了磁通跳跃场与变场速率的关系表达式:Bj=F其规律基本与实验结果相符合,同时从实验中发现磁热不稳定性对永磁体脉冲磁化效果有巨大的影响。 相似文献
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本文用本征模积分方程研究了环形等离子体中磁剪切为负时由电子温度梯度驱动的不稳定性。考虑了电子的全部动力学效应,强调了稳定性阈值附近的模式行为及相应的湍性输运,给出了磁剪切为负的临界梯度的拟合公式。 相似文献
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具有内部输运垒(ITB)的反磁剪切(RS)等离子体位形是在托卡马克中获得高参数的最具前景的途径之一。这种位形不仅改善等离子体约束,而且可以改进象气球模和新经典撕裂模等这类宏观模的稳定性。然而,反磁剪切区域的高压强可以驱动电阻交换模不稳定性,从而破坏中心区的等离子体高参数。为了研究电阻交换模不稳定性的性质,并确定其在RS等离子体中发展的区域,我们利用在HL-2A中使用中性束注入建立的RS位形来分析电阻交换模不稳定性。 相似文献
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本文结合数值计算,给出日冕条件下发生回旋不稳定性的条件。经分析得到离子回旋不稳定性较电子回旋不稳定性优先发生的结论,并讨论由离子回旋不稳定性所产生的电场和加速电子流。 相似文献
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色散阶梯式光纤中的调制不稳定性 总被引:2,自引:1,他引:1
从非线性薛定谔方程出发,研究了理想光纤,普通光纤,色散缓变光纤和色散阶梯式光纤的调制不稳定性,作为实际的应用,随着阶数的增加,色散阶梯式光纤几乎等价于色散缓变光纤。 相似文献
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系统研究了温度、时间、压力等因素对LaFe11.5Si1.5化合物吸氢过程的影响以及效果. 结果表明:吸氢处理会增大化合物的晶格常数,但不会改变其晶体结构. 在温度为423 K,氢气压力为0.0987 MPa时,可以制备出氢分布均匀的LaFe11.5Si1.5H1.6间隙化合物. 氢化处理可以明显提高化合物的居里温度,降低热滞后,并且使磁熵变保持在较高值. LaFe11.5Si1.5H1.6样品随着在空气中暴露时间的延长,居里温度和磁熵值的变化非常小,氢化合金的磁热性能具有良好的时间稳定性.
关键词:
P-C-T关系曲线
居里温度
磁熵变
11.5Si1.5氢化物')" href="#">LaFe11.5Si1.5氢化物 相似文献
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M. Shimizu 《Physics letters. A》1978,68(2):273-274
The possibility of magnetic and elastic instabilities is pointed out from the thermodynamic aspects of the magnetovolume properties of a ferromagnet, and the instabilities, Invar anomalies and martensitic transformations in fcc iron-nickel alloys are discussed. 相似文献
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Hydrogen absorptions of LaFe11.5Si1.5 compound in 1-atm hydrogen gas at different temperatures are investigated. The hydrogen content in the hydrogenated sample does not increase with the increase of temperature of hydrogen absorption but changes complicatedly. The characteristic of first-order transition in LaFe11.5Si1.5 compound is weakened after hydrogen absorption. It leads the peaks of magnetic entropy to become wider and the hysteresis loss to reduce significantly, but relative cooling power (RCP) is not changed considerably. 相似文献
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High-resolution transmission electron microscopy and bulk magnetometry study of LaFe11.5Si1.5 compound 下载免费PDF全文
This paper studies the microstructural and magnetic properties of LaFe11.5Si1.5 compound by means of high-resolution transmission electron microscope and bulk magnetometry measurements. The crystalline structure is accompanied with the noncrystalline and nanocrystalline structures. This characteristic is the reflection of the crystalline process held by quenching. The inverse susceptibilities diverge and deviate from Curie-Weiss law under low applied magnetic fields. This paper proposes the possible mechanism between the anomalous susceptibilities and microstructure, and offers a perspective on the magnetic properties of metastable intermetallic compounds. 相似文献
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The high-temperature phase transition is analyzed according to the DSC of as-cast LaFe11.7 Si1.3 compound and the X-ray patterns of LaFe11.7Si1.3 compounds prepared by high-temperature and short-time annealing. Large amount of 1:13 phase begins to appear in LaFe11.7Si1.3 compound annealed near the melting point of LaFeSi phase (about 1422?K). When the annealing temperature is close to the temperature of peritectic reaction (about 1497?K), the speed of 1:13 phase formation is the fastest. The phase relation and microstructure of the LaFe11.7Si1.3 compounds annealed at 1523?K (5?h), 1373?K (2?h)?+?1523?K (5?h), and 1523?K (7?h) +1373?K (2?h) show that longer time annealing near peritectic reaction is helpful to decrease the impurity phases. For studying the influence of different high-temperature and short-time annealing on magnetic property, the Curie temperature, thermal, and magnetic hystereses, and the magnetocaloric effect of LaFe11.7Si1.3 compound annealed at three different temperatures are also investigated. Three compounds all keep the first order of magnetic transition behavior. The maximal magnetic entropy change ΔSM (T, H) of the samples is 12.9, 16.04, and 23.8?J?kg?1?K?1 under a magnetic field of 0–2?T, respectively. 相似文献
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研究了金属化合物LaFe_(11.5)Al_(1.5)H_x(x=0,0.12,0.6,1.3),LaFe_(11.5)Al_(1.5)B_y(y=0.1,0.2,0.3)和LaFe_(11.5)Al_(1.5)C_z(z=0.1,0.2,0.3,0.4,0.5)的磁性、结构和磁热效应.金属化合物样品均形成了良好的NaZn_(13)型单相结构.基于固相-气相反应或者固相-固相反应引入间隙H,B,C原子后,磁性基态从反铁磁态变为铁磁态,饱和磁化强度(M_s)和居里温度(T_c)均呈升高趋势.值得注意的是:随着B和C含量的增加,化合物的相变性质由弱一级相变过渡至二级相变;而随着H含量的增加,相变性质却从二级相变过渡至弱一级相变.同时,化合物LaFe_(11.5)Al_(1.5)H_x,LaFe_(11.5)Al_(1.5)B_y和LaFe_(11.5)Al_(1.5)C_z均呈现出相当大的磁熵变.在0—5 T的外磁场作用下,LaFe_(11.5)Al_(1.5)H_(1.3),LaFe_(11.5)Al_(1.5)B_(0.1)和LaFe_(11.5)Al_(1.5)C_(0.2)的最大磁熵变分别达到12.3,9.6和10.8 J/kg·K.此外,在0—5 T的外磁场作用下,LaFe_(11.5)Al_(1.5)H_(0.6)的制冷能力达到259.2 J/kg,LaFe_(11.5)Al_(1.5)B_(0.1)的制冷能力达到116.4 J/kg,而LaFe_(11.5)Al_(1.5)C_(0.1)的制冷能力达到230.4 J/kg. 相似文献