FSF三层膜中上临界场的实验和理论分析
Experimental and theoretical analysis of the upper critical field in FSF trilayers
摘要：
在垂直和平行于异质结表面的几何结构下，对薄膜FSF三层自旋阀磁芯的上临界磁场H_{c2}进行了实验和理论研究。利用楔形沉积技术，在单次运行中制备具有底部和顶部Cu_{41} Ni_{59} F层的可变厚度的一系列样品。临界场H_{c2}在温度范围$0.4-8$ K和磁场高达9特斯拉的条件下测量。首次观察到在外加磁场作用下，超导转变温度随F层厚度的变化从振荡转变为折返。为了正确地解释实验数据，我们开发了一个准经典理论，使一个评估的临界场和超导转变温度的温度依赖性的任意一组系统参数。我们的实验数据和理论预测之间的一个相当好的协议证明了所有的样品，使用一组拟合参数。这证实了Fulde-Ferrell-Larkin-Ovchinnikov（FFLO）物理在确定所研究的Cu_{41} Ni_{59} /Nb/ Cu_{41} Ni_{59}自旋阀芯三层的不寻常超导性质方面的充分性。
英文摘要：
The upper critical magnetic field H_{c2} in thin-film FSF trilayer spin-valve cores is studied experimentally and theoretically in geometries perpendicular and parallel to the heterostructure surface. The series of samples with variable thicknesses of the bottom and of the top Cu_{41}Ni_{59} F-layers are prepared in a single run, utilizing a wedge deposition technique. The critical field H_{c2} is measured in the temperature range $0.4-8$ K and for magnetic fields up to 9 Tesla. A transition from oscillatory to reentrant behavior of the superconducting transition temperature versus F-layers thickness, induced by an external magnetic field, has been observed for the first time. In order to properly interpret the experimental data, we develop a quasiclassical theory, enabling one to evaluate the temperature dependence of the critical field and the superconducting transition temperature for an arbitrary set of the system parameters. A fairly good agreement between our experimental data and theoretical predictions is demonstrated for all samples, using a single set of fit parameters. This confirms adequacy of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) physics in determining the unusual superconducting properties of the studied Cu_{41}Ni_{59}/Nb/Cu_{41}Ni_{59} spin-valve core trilayers.
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