Oscillation phenomenon of transition temperatures in Nb/Co and V/Co superconductor/ferromagnet multilayers

Obi, Y.; Ikebe, Manabu; Kubo, Takehiro; Fujimori, H.

doi:10.1016/s0921-4534(99)00055-6

Cited by 54 publications

(45 citation statements)

References 14 publications

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“…The following experiments 7,8,9,10,11,12,13 revealed the different and even controversial behavior of T c (d F ) for different structures. The nonmonotonic oscillation-like behavior of T c (d F ) was reported by Jiang et al 7 for Nb/Gd multilayers and Nb/Gd/Nb trilayers, by Mühge et al 8 for Fe/Nb/Fe trilayers and recently by Obi et al 9 for Nb/Co and V/Co multilayers. However, negative results were reported for Nb/Gd/Nb trilayers by Strunk et al 10 , for V/V 1−x Fe x multilayers by Aarts et al 11 , for Fe/Nb bilayers by Mühge et al 12 and Nb/Fe multilayers by Verbanck et al 13 .…”

Section: Introductionmentioning

confidence: 90%

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Theory of proximity effect in superconductor/ferromagnet heterostructures

2003

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We present a microscopic theory of proximity effect in the ferromagnet/superconductor-/ferromagnet (F/S/F) nanostructures where S is s-wave low-Tc superconductor and F's are layers of 3d transition ferromagnetic metal. Our approach is based on the direct analytical solution of Gor'kov equations for the normal and anomalous Green's functions together with a self-consistent evaluation of the superconducting order parameter. We take into account the elastic spin-conserving scattering of the electrons assuming s-wave scattering in the S layer and s-d scattering in the F layers. In accordance with the previous quasiclassical theories, we found that due to exchange field in the ferromagnet the anomalous Green's function F (z) exhibits the damping oscillations in the F-layer as a function of distance z from the S/F interface. In the given model a half of period of oscillations is determined by the length ξ 0 m = πvF /εex, where vF is the Fermi velocity and εex is the exchange field, while damping is governed by the length l0 = (1/l ↑ + 1/l ↓ ) −1 with l ↑ and l ↓ being spin-dependent mean free paths in the ferromagnet. The superconducting transition temperature Tc(dF ) of the F/S/F trilayer shows the damping oscillations as a function of the F-layer thickness dF with period ξF = π/ √ mεex, where m is the effective electron mass. The oscillations of Tc(dF ) are a consequence of the oscillatory behavior of the superconducting order parameter at the S/F interface vs thickness dF , that in turn is caused by the oscillations of F (z) in the F-region. We show that strong spin-conserving scattering either in the superconductor or in the ferromagnet significantly suppresses these oscillations. The calculated Tc(dF ) dependences are compared with existing experimental data for Fe/Nb/Fe trilayers and Nb/Co multilayers.

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Section: Introductionmentioning

confidence: 90%

“…Let us consider the experiments on Nb/Co multilayers by Obi et al 9 . The theoretical curve T c (d F ) in comparsion with experimental data is shown in Fig.…”

Section: B Comparison With Experimentsmentioning

confidence: 99%

Theory of proximity effect in superconductor/ferromagnet heterostructures

2003

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“…Transitions can be observed as oscillations in the critical temperature (T c ) of S/F multilayers [4,5,6,7] as well as oscillations in the I c of S/F/S junctions with both thickness of the F layer [8,9,10] and, for weak ferromagnets whose exchange energy (E ex ) is comparable to k B T c of the superconductor, with temperature [11].…”

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confidence: 99%

Critical Current Oscillations in Strong FerromagneticπJunctions

et al. 2006

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We report magnetic and electrical measurements of Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni and Ni80Fe20 (Py). All these materials show multiple oscillations of critical current with barrier thickness implying repeated 0-π phase-transitions in the superconducting order parameter. We show in particular that the Co barrier devices can be accurately modelled using existing clean limit theories and so that, despite the high exchange energy (309 meV), the large IcRN value in the π-state means Co barriers are ideally suited to the practical development of superconducting π-shift devices.

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“…5 The oscillatory order parameter brings about an oscillation of the superconducting transition temperature T c as a function of the F-layer thickness, which has been observed in various experiments. 6,7 This phenomenon is reasonably well understood and described by theoretical models. As for the existence of long-range triplets, two experiment has been reported thus far, 8,9 but their existence is not yet fully accepted.…”

Section: Introductionmentioning

confidence: 84%

Domain-wall enhancement of superconductivity in superconductor/ferromagnet hybrids: Case of weak ferromagnets

Flokstra

Aarts

2009

Phys. Rev. B

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We use magnetotransport measurements to study the influence of the domain structure on the superconducting transition temperature T c in ferromagnetic ͑F͒/superconducting ͑S͒ bilayers and F / S / F trilayers based on Nb and the weak ferromagnet Cu 43 Ni 57 . By comparing the anisotropic magnetoresistance above T c with the resistance behavior in the transition and with critical current measurements below T c , we show that in bilayers enhanced superconductivity is found when the F layer is in a domain state. We also find that, below T c , the magnetic fields where domains occur are significantly higher than above or around T c , suggesting that the magnetization rotation in the F layers is influenced by the adjacent superconductor. In trilayers the effects are similar. A domain-state dominated mechanism even for reported spin-valve effects therefore cannot be ruled out.

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Oscillation phenomenon of transition temperatures in Nb/Co and V/Co superconductor/ferromagnet multilayers

Cited by 54 publications

References 14 publications

Theory of proximity effect in superconductor/ferromagnet heterostructures

Theory of proximity effect in superconductor/ferromagnet heterostructures

Critical Current Oscillations in Strong FerromagneticπJunctions

Domain-wall enhancement of superconductivity in superconductor/ferromagnet hybrids: Case of weak ferromagnets

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