New Ce heavy-fermion system: CeCu6
New Ce heavy-fermion system: CeCu6
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DOI：
10.1103/physrevb.30.482
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发表时间：
1984-07
影响因子：
3.7
通讯作者：
G. Stewart;Z. Fisk;M. Wire
中科院分区：
文献类型：
--
作者：
G. Stewart;Z. Fisk;M. Wire
物理评论B卷30，1号新Ce重费米子系统：1984年7月CeCu6 G.R.Stewart，Z.Fisk和M.S.Wire材料科学和技术部，Los A/Amos国家实验室，Los Alamos，新墨西哥州87545(1984年4月24日收到)我们在1.5K发现了emu/moleG)MJ/Molek在1.8K和热测量结果一致(X=0)。027一个新的重费米子系统CeCu6，具有大的磁化率和低于10K的大的随温度变化的比热y，即840，在T=O时外推到1，6J/Molek，类似于CeA13。高场特性--与窄带图像几乎完美地结合在一起，这是首次为UBE~3提出的。自从Steglich等人的发现以来。1979年，在CeCu2Si2的块体超导性研究中，人们对这些所谓的重费米子系统产生了极大的兴趣。CeCu2Si2是一个具有高关联电子的电子系统，其有效质量大约是裸电子质量的200倍。作为一类材料，迄今已知的7个重费米子系统都含有电子，并且具有大的比热y值(C=yT+/3t3，由此计算出大的有效质量)，大的4A)4f或sf原子间距，遵循居里-魏斯定律的高温磁化率，大的低温磁化率，以及它们的电阻率通常与温度有关。这七个系统在低温下可能被划分为超导的，‘磁性的，或者像CeA13[y(T=0)=1.6J/mole K2]和UC？Npa6sBe3[y(T=O)1.1J/mole K]的情况。除了三个系统外，所有这些系统都具有温度的快速函数y‘s，从10K时的200mJ/mole K’到1K以下的1000mJ/mole K2以上。我们集中在具有大的f原子分离的Ce和U化合物上寻找其他重费米子系统，这些化合物在低温下没有磁有序-我们在这里报道了CeCu6，一种正交的温度特性。当Ce被一个由19个铜原子组成的笼子包围，Ce-Ce间距为4.83A时，我们在Los Alamos首次解决了结构问题。我们测量了由纯组元组成的材料在零场和11T场下的电阻率为1.4-300K，直流电感为1.4-100K，比热为1.8-38fK。用X射线粉末衍射仪对其进行了表征。交流磁化率的测量表明，没有证据表明超导电性下降到0。用标准四探针法测量的电阻率数据如图1所示。数据在29K左右有一个最小值，在11K有一个宽大的最大值，在较低的温度下有一个急剧下降。直流磁化率，如图2所示，是在一块69毫克的弧焊按钮上用法拉第天平测量的。在77K以上，CeCu6的磁化率数据已经在文献中报道过，并与我们在重叠区的数据一致。测量了CeCu6在1.5K，0。027emu/moleG很大，是UAE~3的近似值的两倍。同样值得注意的是，我们的磁化率数据在30K左右有一个明确的特征，它与最小电阻率很好地对应。图3所示的零场比热是在用于磁化率测量的同一块材料上用小样量热计测量的。在低于8K的温度下，我们看到CjT迅速增加，这是大多数重费密子系统的特征。事实上，这些低温数据与CeA13公布的比热结果相差不到几个百分点。因此，我们预计CeCu6的y(T=0)值也约为1.6J/摩尔k2。U E E O 1 x I Q I温度(K)图1，CeCu6的最小I电阻率与大约29K时的温度之比。注1 L温度(K)见图2。CeCu6的磁化率与温度的关系。注意在大约30K时的轻微驼峰，77K左右的失配在起源上是有帮助的。1984年美国物理学会
PHYSICAL REVIEW B VOLUME 30, NUMBER 1 New Ce heavy-fermion system: JULY 1984 CeCu6 G. R. Stewart, Z. Fisk, and M. S. Wire Materials Science and Technology Division, Los A/amos National Laboratory, Los Alamos, New Mexico 87545 (Received 24 April 1984) We have discovered emu/moleG at 1. 5 K) mJ/moleK at 1. 8 K and heat measurements agree (X=0. 027 a new heavy-fermion system, CeCu6, with a large susceptibility and a large, temperature-dependent specific heat y below 10 K that is 840 extrapolates to 1,6 J/moleK at T=O in analogy with CeA13. High-field specific- almost perfectly with a narrow-band picture first proposed for UBe~3. Since the discovery' by Steglich et al. in 1979 of bulk su- perconductivity in CeCu2Si2, an electron system with high- ly correlated electrons having effective masses about 200 times the bare-electron mass, a great deal of interest has focused on these so called heavy-fermion systems. As a class of materials, the seven heavy-fermion systems known' 7 to date all contain electrons and have large specific-heat y values (C= y T+/3T3, from which the large effective masses are calculated), a large 4 A) 4f or Sf atom separation, a high-temperature susceptibility that fol- lows a Curie-Weiss law, a large low-temperature susceptibili- ty, and usual temperature dependence in their resistivity. A possible division of these seven sytems at low temperatures in between those that go superconducting, ' magnetic, or neither6 7 as is the case in CeA13 [y( T = 0) = 1. 6 J/mole K2] and Uc»Npa6sBei3 [y(T=O) 1. 1 J/mole K ]. All but three of these systems have y's that are rapid functions of temperature, varying from under 200 mJ/mole K' at 10 K to over 1000 mJ/mole K2 below 1 K. We have focused a search for other heavy-fermion sys- tems on Ce and U compounds with large f-atom separa- tions that are not known to order magnetically at low tem- We report here on CeCu6, an orthorhombic peratures. structure first solved at Los Alamos with Ce surrounded by a cage of 19 Cu atoms and a Ce-Ce spacing of 4. 83 A. We have measured the resistivity from 1. 4 to 300 K, dc suscep- tibility from 1. 4 to 100 K, and specific heat from 1. 8 to 38 f f K in zero and 11 T applied field on material prepared by arc melting together the pure constituents and characterized as single phase by x-ray powder diffraction. Measurements of the ac susceptibility showed no evidence of superconductivi- ty down to 0. 040 K. The resistivity data measured by a standard four probe technique are shown in Fig. 1. The data have a minimum at about 29 K and a broad maximum centered at 11 K, with a sharp drop at lower temperatures. The dc susceptibility, shown in Fig. 2, was measured in a Faraday balance on a 69 mg piece of the arc melted button. Susceptibility data for CeCu6 above 77 K have been reported in the literature and agree with our data in the region of overlap. The magni- tude of our measured susceptibility for CeCu6 at 1. 5 K, 0. 027 emu/moleG is enormous twice the approximately value found for Uae~3. Also noteworthy in our susceptibil- ity data is the definite feature at about 30 K, which corre- lates well with the resistivity minimum. The specific heat in zero field from 1. 8 to 38 K, shown in Fig. 3, was measured in a small sample calorimeter on the same piece of material used for the susceptibility measure- ments. At temperatures below 8 K we see the rapid in- crease in Cj T that is characteristic of most heavy-fermion sytems. In fact, these low-temperature data are within a few percent of published specific heat results for CeA13. Thus, we expect the y(T = 0) value for CeCu6 to also be about 1. 6 J/mole K2. U E E O O. O1 x I Q I TEMPERATURE (K) FIG. 1, minimum I Resistivity vs at around 29 K. temperature for CeCu6. Note I l TEMPERATURE (K) the FIG. 2. Susceptibility vs temperature for CeCu6. Note the slight hump at about 30 K. The mismatch around 77 K is instrumental in origin. C'1984 The American Physical Society