Evidence for spin selectivity of triplet pairs in superconducting spin valves

Banerjee, Niladri; Smiet, Christopher Berg; Smits, R. G. J.; Ozaeta, Asier; Bergeret, F. S.; Blamire, M. G.; Robinson, Jason Joseph

doi:10.1038/ncomms4048

Cited by 88 publications

(51 citation statements)

References 40 publications

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“…Such a behavior has been confirmed by analysis of the inverse proximity effect (i.e., suppression of superconductivity in an S-layer in contact with a ferromagnet) for F/S/F [16,17] and S/F/F [18] structures.…”

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confidence: 66%

Controllable generation of a spin-triplet supercurrent in a Josephson spin valve

2014

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It has been predicted theoretically that an unconventional odd-frequency spin-triplet component of superconducting order parameter can be induced in multilayered ferromagnetic structures with non-collinear magnetization. In this work we study experimentally nano-scale devices, in which a ferromagnetic spin valve is embedded into a Josephson junction. We demonstrate two ways of in-situ analysis of such Josephson spin valves: via magnetoresistance measurements and via in-situ magnetometry based on flux quantization in the junction. We observe that supercurrent through the device depends on the relative orientation of magnetization of the two ferromagnetic layers and is enhanced in the non-collinear state of the spin valve. This provides a direct prove of controllable generation of the spin-triplet superconducting component in a ferromagnet.An interplay of superconductivity (S) and ferromagnetism (F) in hybrid S/F heterostructures leads to a variety of unusual physical phenomena [1][2][3][4][5][6][7][8][9][10]. Of particular interest is a possibility of generation of an unconventional odd-frequency spin-triplet component of the superconducting condensate [2,7]. The ferromagnetic exchange energy is usually much larger than the superconducting energy gap. Consequently, a conventional spin-singlet superconducting order parameter decays at a short range ∼ 1 nm in a spatially uniform, mono-domain ferromagnet. Experimental observations of a long-range proximity effect through strong ferromagnets [11,12] and, in particular, through almost fully spin-polarized half-metals [13][14][15] is consistent with appearance of the spin-triplet component, which is insensitive to strong magnetic and exchange fields. However, it may also be due to various types of artifacts and, at certain circumstances, a longrange spin-singlet component can be realized in clean S/F heterostructures [9]. Therefore, unambiguous confirmation for existence of the spin-triplet superconductivity in S/F heterostructures requires controllable tunability of the phenomenon. This is also prerequisite for potential applications of S/F heterostructures in spintronics.The spin-triplet order parameter in S/F heterostructures is generated in presence of an active spin-mixing interface [5,7] or in case of a spatially non-uniform distribution of magnetization [2]. The latter can be achieved in spin valve structures with several F-layers [1,3,6,[8][9][10]. Both the spin-singlet and the spin-triplet components depend on the angle between magnetization of F-layers in such superconducting spin valves. The spin-singlet component is at maximum for the antiparallel (AP) and minimum at the parallel (P) state of the spin valve [9]. The spin-triplet component is maximum at the non-collinear state with 90• misalignment between magnetic moments and zero both in P-and AP-states [3,8]. Such a behavior has been confirmed by analysis of the inverse proximity effect (i.e

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confidence: 66%

Controllable generation of a spin-triplet supercurrent in a Josephson spin valve

2014

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“…This includes GMR and TMR spin valves [ 35 ] for magnetic sensors, magnetoresistive random access memory (MRAM) cells and a multitude of systems that are based on spin-transfer torque. The large parameter range of coercivities and easy axes orientations possible in one single device will lead to qualitative advances, e.g., new types of 3D multilevel magnetic memory cells [ 36,37 ] and the design of switchable ferromagnetic/nonmagnetic hybrid structures (e.g., ferromagnet/superconductor hybrids [ 38 ] ).…”

Section: Discussionmentioning

confidence: 99%

Spin‐Structured Multilayers: A New Class of Materials for Precision Spintronics

Schlage

Bocklage

Erb

et al. 2016

Adv Funct Materials

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7423wileyonlinelibrary.com extensively explored to maximize the magnitude of the magnetoresistive signal, which is defi ned as the normalized difference of the electrical resistance in the antiparallel and parallel magnetic confi guration of the trilayer. The basic GMR and TMR characteristics of spintronic devices and thus their functionalities, however, did not signifi cantly change during the last decade. This is due to conventional magnetic multilayer design and its limitations based on the interplay of accessible magnetic anisotropy contributions. Here, we show that oblique incidence deposition (OID) can be used in an elegant way to achieve full control on the magnetic anisotropy in every individual layer of such magnetoresistive multilayer stacks for the fi rst time. The additional shape anisotropy component introduced via OID allows for arbitrarily crossed magnetic easy axes with adjustable switching fi elds and opens a path for customized spintronic devices with conceptually new functionalities.So far, two major approaches have been pursued to engineer fi eld-dependent relative magnetic confi gurations of two ferromagnetic layers. In the fi rst case, one of the ferromagnetic layers either exhibits an enhanced coercive fi eld or is magnetically pinned (exchange biased) by an additional antiferromagnetic layer of high magnetic anisotropy. Thus, only the magnetically uncoupled free layer follows small external fi elds, causing a change of the magnetic confi guration and the magnetoresistance. [ 13 ] In the second approach, an interlayer exchange coupling, the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction, is used to align both layers relative to each other. [ 14 ] The interlayer coupling defi nes the magnetic saturation behavior and hence the functionality of the trilayer. In conventional systems, only parallel or antiparallel orientations of the ferromagnetic layers are reliably achieved. Effi cient RKKY coupling is observed for particular material combinations only and depends very sensitively on the interlayer thickness. [ 15,16 ] Therefore, conventional magnetic multilayer design is restricted to a limited number of magnetic confi gurations in the trilayers which constrains the design and control of magnetic spin structures that are available for realizing particular magnetoelectronic responses.Our approach enables one to realize and tune magnetic and magnetoresistive properties in spintronic multilayer systems that exceed the potential of conventional approaches by far. The technique is not based on exchange-bias or interlayer coupling and is not affected by their limitations. Every ferromagnetic layer of arbitrary chemical composition, as a constituent either Spin-Structured Multilayers: A New Class of Materials for Precision SpintronicsKai Schlage , * Lars Bocklage , Denise Erb , Jade Comfort , Hans-Christian Wille , and Ralf Röhlsberger * Magnetoelectronic multilayer devices are widely used in today's information and sensor technology. Their functionality, however, is limited by the inherent prop...

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“…The observed angular dependence of the superconducting transition temperature T c is caused by a combination of the singlet and triplet components of the superconducting condensate. The existence of the triplet contribution to the superconducting spin-valve effect has also been shown in [11][12][13][14][15]. An important question for basic and applied research in the field of spintronics is whether there is the possibility of observing the "isolated" triplet contribution to the superconducting spin-valve effect.…”

Section: Introductionmentioning

confidence: 85%

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

et al. 2018

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Abstract. In the present work we have studied the proximity-induced superconducting triplet pairing in CoO x /Py1/Cu/Py2/Cu/Pb spin-valve structure (where Py = Ni 0.81 Fe 0.19 ).For CoO x (3 nm)/Py(3 nm)/Cu(4 nm)/Py(0.6 nm)/Cu(2 nm)/Pb(70 nm) we have studied the dependence of the T c on the angle α between the direction of the cooling field and the external field both applied in the plane of the sample. We obtained that the T c does not change monotonically with the angle but passes through a minimum. To observe an "isolated" triplet spin-valve effect we exploited the oscillatory feature of the magnitude of the ordinary spin-valve effect ∆T c in the dependence of the Py2-layer thickness d Py2 . We determined the value of d Py2 at which ∆T c caused by the ordinary spin-valve effect is suppressed. This means that the difference in the T c between the antiparallel and parallel mutual orientation of magnetizations of the Py1 and Py2 layers is zero. For such a sample a "pure" triplet spin-valve effect which causes the minimum in T c at the orthogonal configuration of magnetizations has been observed.

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Evidence for spin selectivity of triplet pairs in superconducting spin valves

Cited by 88 publications

References 40 publications

Controllable generation of a spin-triplet supercurrent in a Josephson spin valve

Controllable generation of a spin-triplet supercurrent in a Josephson spin valve

Spin‐Structured Multilayers: A New Class of Materials for Precision Spintronics

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

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