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arXiv 1111.4760cond-mat.supr-concond-mat.mtrl-scicond-mat.str-el
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超导铁磁体RuSr2Gd1.4Ce 0.6Cu_2 O_(10-δ)的specific heat曲线中的交叉点现象(T ~* = 2.7 K)

Crossing point phenomena (T* = 2.7 K) in specific heat curves of superconducting ferromagnets RuSr2Gd1.4Ce0.6Cu2O10-δ

Anuj Kumar, R. P. Tandon, Jianli Wang, Rong Zeng, V. P. S. Awana

摘要:

交叉点现象是强关联电子系统中一个有趣而又令人困惑的现象。采用标准固相反应法合成了RuSr_2Gd_(1.4)Ce_(0.6)Cu_2 O_(10-δ)(GdRu-1222)磁性超导体,并对其磁性、输运和热性质进行了测量。我们还合成了RuSr_2 Eu_(1.4)Ce_(0.6)Cu_2 O_(10-δ)(EuRu-1222),并测量了它在零磁场下的热容。所研究的化合物均为四方晶系,空间群为I4/mmm。GdRu-1222是一种磁性超导体,在110 K附近具有Ru自旋磁有序性,在40 K以下具有Cu-O 2平面的超导性。为了探索交叉点现象,比热[Cp(T)]在温度范围1.9-250 K,磁场高达70 kOe下进行了研究。不幸的是,虽然在比热中没有观察到磁性和超导转变,但在低于20 K的低温下观察到肖特基型异常。这种低温Schottky型异常可以归因于顺磁Gd 3+离子的基态光谱项8 S 7/2被内部和外部磁场分裂。还观察到,对于不同的磁场值测量的Cp(T)具有相同的交叉点(T* = 2.7 K),直到施加的磁场70 kOe。这种现象的定量解释,根据其形状和相关的广义热容(Cp)的温度依赖性,提出。这种效应支持交叉点现象,这应该是固有的强关联系统。

英文摘要:

Crossing point phenomena are one of the interesting and still puzzling effects in strongly correlated electron systems. We have synthesized RuSr2Gd1.4Ce0.6Cu2O10-δ (GdRu-1222) magneto-superconductor through standard solid state reaction route and measured its magnetic, transport and thermal properties. We also synthesized RuSr2Eu1.4Ce0.6Cu2O10-δ (EuRu-1222) then measured its heat capacity in zero magnetic fields for reference. The studied compounds crystallized in tetragonal structure with space group I4/mmm. GdRu-1222 is a reported magneto-superconductor with Ru spins magnetic ordering at temperature around 110 K and superconductivity in Cu-O2 planes below around 40 K. To explore the crossing point phenomena, the specific heat [Cp (T)] was investigated in temperature range 1.9-250 K, under magnetic field of up to 70 kOe. Unfortunately though no magnetic and superconducting transitions are observed in specific heat, a Schottky type anomaly is observed at low temperatures below 20 K. This low temperature Schottky type anomaly can be attributed to splitting of the ground state spectroscopic term 8S7/2 of paramagnetic Gd3+ ions by both internal and external magnetic fields. It was also observed that Cp (T) being measured for different values of magnetic field, possesses the same crossing point (T* = 2.7 K), up to the applied magnetic field 70 kOe. A quantitative explanation of this phenomenon, based on its shape and temperature dependence of the associated generalized heat capacity (Cp), is presented. This effect supports the crossing point phenomena, which is supposed to be inherent for strongly correlated systems.

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