Isolation of proximity-induced triplet pairing channel in a superconductor/ferromagnet spin valve

Abstract

We have studied the proximity-induced superconducting triplet pairing in CoOx/Py1/Cu/Py2/Cu/Pb spin-valve structure (where Py = Ni0.81Fe0.19).By optimizing the parameters of this structure we found a triplet-channel assisted full switching between the normal and superconducting states. To observe an "isolated" triplet spin-valve effect we exploited the oscillatory feature of the magnitude of the ordinary spin-valve effect ∆Tc in the dependence of the Py2-layer thickness dP y2. We determined the value of dP y2 at which ∆Tc caused by the ordinary spin-valve effect (the difference in the superconducting transition temperature Tc between the antiparallel and parallel mutual orientation of magnetizations of the Py1 and Py2 layers) is suppressed. For such a sample a "pure" triplet spin-valve effect which causes the minimum in Tc at the orthogonal configuration of magnetizations has been observed.The superconducting spin-valve effect consists of different degree of suppression of superconductivity in the F1/F2/S or F1/S/F2 thin film multilayer constructions at parallel (P) and antiparallel (AP) mutual orientation of magnetizations of the F1 and F2 ferromagnetic layers. The superconducting spin valves based on the superconductor/ferromagnet (S/F) proximity effect offer a playground to explore fundamental aspects of interplay between superconductivity and magnetism and also promise applications as passive devices of the superconducting spintronics. The latter construction should be operational upon application of a small external magnetic field. Many experimental works were performed to confirm this effect for the S/F systems with a good contact between metallic F and S layers made of ordinary metals and standard ferromagnets (see, e.g., recent reviews [6]), the full switching between the superconducting and normal states has been realized only in a few cases [7,8] because ∆T c was usually smaller than the width of the superconducting transition δT c .Very recently, Singh et al. reported [9] the observation of a colossal triplet spin-valve effect for the S/F1/N/F2 structure made of amorphous MoGe, Ni, Cu, and CrO 2 as the S, F1, N, and F2 layers, respectively. This structure demonstrated variation of T c by ∼ 1 K when changing the relative alignment of the two F layers. It was shown that the optimal operational field for this device is of the order of 20 kOe. Gu et al. [10,11] reported ∆T c ∼ 400 mK for Ho/Nb/Ho trilayers. Also in this case the parallel configuration of magnetizations was reached at a field of ∼ 10 kOe. The high operational fields of these spin valves are disadvantageous for the superconducting spintronics. Besides, the physical reasons for large values of ∆T c for spin valve based on half-metals are not yet theoretically explained. This calls for elaboration of classical spinvalve structures which use standard ferromagnets (Fe, Co, Ni) and their alloys with good electrical contacts between all layers and for which theoretical understanding of the operational principle is available.Oh et al. [12] propos...

Superconducting switching due to a triplet component in the Pb/Cu/Ni/Cu/Co2Cr1−xFexAly spin-valve structure

“…3 depicts the dependence of T c on α for the sample PLAK4216. It appears qualitatively similar to the ones observed by us previously ([9,13,15,21,23–26]), reaching a minimum near α = 90°. However, the minimum that we observe now is much deeper, suggesting that the SSV effect is dominated by the spin polarized (triplet) Cooper pairs.…”

Control of Superconductivity with a Single Ferromagnetic Layer in Niobium/Erbium Bilayers

“…The prototypical super-spintronic device is the superconducting spin valve. In this device, control of the magnetic state of the two F-layers in an S/F/F or F/S/F heterostructure can be used to tune the generation of the LRTC [10][11][12][13][14][15]. The generation of the LRTC opens an additional conduction channel for Cooper pairs, resulting in the lowering of T c [16].…”

Сверхпроводящие Спиновые Вентили На Основе Спиральных Магнетиков

“…Потенциальный барьер, разделяющий состояния спирального магнитного элемента с разными значения- ми T c , обеспечивает дискретность переключения такого элемента памяти, что должно решить проблему полувыбора. Этим свойством не обладают триплетные структуры, исследовавшиеся ранее, с непрерывным вращением намагниченности одного из ферромагнитных слоев [16][17][18][19][20][21][22][23][24][25][26].…”

“…Влияние LRTC на эффект близости в спиновых вентилях было обнаружено в экспериментальных работах [16][17][18][19][20][21][22]. Прямая связь между образованием спин-поляризованных триплетных корреляций и подавлением T c наблюдалась в сверхпроводящих спиновых вентилях в работах [20,[23][24][25][26]. При этом было обнаружено, что критическая температура уменьшается сильнее в случае неколлинеарных намагниченностей, чем в коллинеарных конфигурациях (антипараллельных или параллельных).…”

“…При этом было обнаружено, что критическая температура уменьшается сильнее в случае неколлинеарных намагниченностей, чем в коллинеарных конфигурациях (антипараллельных или параллельных). Полное переключение из состояния сверхпроводника в состояние нормального металла требует такого уменьшения критической температуры, которое преодолевает типичную ширину сверхпроводящего перехода и было достигнуто с использованием LRTC [24].…”