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，f层磁化（M1, M2）的非共线取向会产生奇数频S波三重态配对。由于等自旋配对是由f -金属的磁化导带支持的，因此这种配对通道在f层中具有超长的距离。该成分的产生显著影响了超导接近效应自旋阀设计F1/S/F2和S/F1/F2的转变温度。对于S/F1/F2体系，理论预测了接近M1和M2交叉构型的超导转变温度的绝对最小值。如果f层是磁性合金，这种效应预计会很大（在不同的磁化排列之间为1K数量级）。特别是对于这些材料，我们想研究本工作中的现象，并将其与F1/S/F2结构中的相应现象进行比较。然而，稀释铁磁合金层的交换偏置是一项困难的任务。因此，我们最近改进的铁磁层交换偏置的方法（对于稀释的铁磁合金尤其重要）将被应用。通过这种方式，我们还希望实现1K级的大标准（或逆）自旋阀效应，正如在平行和反平行磁化排列之间的临界温度差异所期望的那样，其中频率上的奇数s波三重态配对产生不存在。此外，我们期望解决长期存在的自旋阀效应与磁场效应的区分问题。为了研究我们的系统中三重态组分和电流输运的相互影响，我们将研究在不同外加磁场和临界电流下的自旋阀效应。由于我们最近在F/S/F型自旋阀结构中的记忆效应实验显示了非平衡效应的证据，我们最终希望对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.