Comparison of magneto-superconductive properties of RuSr2GdCu2O8−δ and RuSr2Gd1.5Ce0.5Cu2O10−δ
Comparison of magneto-superconductive properties of RuSr2GdCu2O8−δ and RuSr2Gd1.5Ce0.5Cu2O10−δ
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RuSr2GdCu2O8−δ 和 RuSr2Gd1.5Ce0.5Cu2O10−δ 的磁超导性能比较
DOI：
10.1016/s0921-4534(02)01422-3
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发表时间：
2002
影响因子：
1.7
通讯作者：
H. Yamauchi
中科院分区：
文献类型：
--
作者：
V. Awana;S. Ichihara;M. Karppinen;H. Yamauchi
摘要RuSr2GdCu2O8−δ (Ru-1212)和RuSr2Gd1。通过固相反应途径合成了5Ce−0.5 Cu2O10−δ (Ru-1222)。前者在P4/mmm空间群结晶，后者在I4/mmm空间群结晶。在5-Oe场中测量的磁化温度曲线显示，Ru-1212和Ru-1222分别在140和100 K左右有明显的零场冷（ZFC）和场冷（FC）曲线分支，在135和80 K处有尖峰，在20和30 K左右只有ZFC分支出现反磁转变。在135k和80k处的两个下降尖峰可能归因于Ru自旋的反铁磁性。在低于50 K的低温下，由于铁磁成分的存在，两种样品的等温磁化具有非线性贡献。Ru-1212样品在0、3和7 T磁场下的电阻-温度行为证实了超导性，表现出与传统高tc超导体不同的超导跃迁展宽类型。在135 K时，在Ru磁有序温度以上，磁电阻为负。在Ru的磁有序温度以下，Ru-1212在低场呈正峰，在高场呈负峰。对于Ru-1222， MR在定序温度上下均为负值。在Ru磁有序温度下，最大负MR值为2%。来自Ru-1212样品的电子衍射（ED）图显示了两种类型的上层结构：一种在a∗-b∗矩形的中心有弱点，另一种只在b∗边缘的中心有弱点。后者表明沿b方向发生了Ru/Cu或2b周期的空位排序。有趣的是，Ru-1222显示的ED模式只有干净的a∗-b∗和a∗-c∗平面，没有任何超黑点。
Abstract Samples of compositions, RuSr2GdCu2O8− δ (Ru-1212) and RuSr2Gd1. 5Ce− 0.5 Cu2O10− δ (Ru-1222), were synthesised through solid-state reaction routes. The former crystallized in the space group P4/mmm and the latter in I4/mmm. The magnetization vs. temperature curve measured in 5-Oe field showed a clear branching into zero-field-cooled (ZFC) and field-cooled (FC) curves for Ru-1212 and Ru-1222, respectively, around 140 and 100 K with a cusp at 135 and 80 K and a diamagnetic transition around 20 and 30 K only in the ZFC branch. The two down-turn cusps at 135 and 80 K may be attributed to the antiferromagnetic nature of Ru spins. The isothermal magnetization possessed a non-linear contribution due to a ferromagnetic component at low temperatures below 50 K for both samples. The resistance vs. temperature behaviour of the Ru-1212 samples in applied fields of 0, 3 and 7 T confirmed superconductivity, exhibiting a different type of broadening of the superconductivity transition under magnetic fields from that known for conventional high-Tc superconductors. The magnetoresistance (MR) was negative above the Ru magnetic ordering temperature at 135 K. Below the Ru magnetic ordering temperature MR displayed a positive peak at low fields and became negative at higher fields for Ru-1212. For Ru-1222 MR remained negative both above and below the ordering temperature. A maximum of 2% was observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction (ED) pattern from the Ru-1212 sample showed two types of superstructure: one has a weak spot at the centre of the a∗–b∗ rectangle, and the other at the center of the b∗ edge only. The latter indicates that either Ru/Cu or vacancy ordering of 2b periodicity takes place along the b-direction. Interestingly, Ru-1222 showed only ED patterns with clean a∗–b∗ and a∗–c∗ planes without any superspots.