Study of Unconventional Triplet Superconductivity and Spin-Valve Effects in Superconductor/Ferromagnet Nanolayered Heterostructures

在超导（S）和两个铁磁（F1，F2）纳米层的异质结构中，对于F层的磁化（M1，M2）的非共线取向，发生奇数频率s波三重态配对生成。这种配对通道在F层中具有非常长的范围，因为等自旋配对由F金属的磁化导带支持。该分量的产生显著地影响两种超导邻近效应自旋阀设计F1/S/F2和S/F1/F2的转变温度。 对于S/F1/F2系统，理论预测超导转变温度的绝对最小值接近于M1和M2的交叉位形。如果F层是磁性合金，则预期该效应是大的（在磁化的不同排列之间为1 K量级）。特别是对于这些材料，我们希望在本工作中研究的现象，并将其与F1/S/F2结构中的相应现象进行比较。然而，由稀释的铁磁合金制成的层的交换偏置是一项困难的任务。 因此，我们最近改进的方法，以交换偏置的铁磁层之一（特别是重要的稀释铁磁合金）将被应用。 通过这种方式，我们还希望实现1 K量级的大的标准（或逆）自旋阀效应，正如预期的那样，平行和反平行磁化排列之间的临界温度差，对于这种情况，不存在频率为奇数的s波三重态配对。 此外，我们期望解决长期存在的问题，区分自旋阀效应和磁杂散场效应。 为了研究三重态组分和电流输运的相互影响，我们将在不同的外加磁场和电流下研究自旋阀效应。 由于我们最近在F/S/F型自旋阀结构中的记忆效应的实验已经显示出非平衡效应的证据，我们最终想对S-F异质结构中的非平衡超导性进行初步研究。

In heterostructures of a superconducting (S) and two ferromagnetic (F1,F2) nanolayers an odd in frequency s-wave triplet pairing generation occurs for a non-collinear orientation of the magnetizations (M1, M2) of the F-layers. This pairing channel is of extraordinary long range in the F-layers, because the equal-spin pairing is supported by the magnetized conduction band of the F-metal. The generation of this component significantly affects the transition temperature of both superconducting proximity effect spin-valve designs, F1/S/F2 and S/F1/F2. For the S/F1/F2 system the theory predicts an absolute minimum of the superconducting transition temperature close to the crossed configuration of M1 and M2. This effect is expected to be large (of order 1K between different alignments of the magnetizations) if the F-layers are magnetic alloys. Especially for these materials, we want to investigate the phenomenon in the present work and compare it with the corresponding phenomenon in F1/S/F2 structures. However, exchange biasing of a layer made of a diluted ferromagnetic alloy is a difficult task. Therefore, our recently improved method to exchange bias one of the ferromagnetic layers (especially important for a diluted ferromagnetic alloy) will be applied. In this way we also want to realize a large standard (or inverse) spin-valve effect of order 1K, as expected for the difference in the critical temperatures between parallel and antiparallel alignment of the magnetizations, for which the odd in frequency s-wave triplet pairing generation is not present. Moreover, we expect to solve the long-standing problem to distinguish the spin-valve effects from magnetic stray-field effects. To study the mutual influence of triplet components and the current transport in our systems, the spin-valve effects will be investigated at different applied magnetic fields and currents up to the critical one. Since our recent experiments on memory effects in a F/S/F type spin valve structure have shown evidence of non-equilibrium effects, we finally want to perform a pilot study on non-equilibrium superconductivity in S-F-heterostructures.