ROLE OF NORMAL INTERLAYER IN FERROMAGNETIC JOSEPHSON JUNCTIONSтезисы доклада

Дата последнего поиска статьи во внешних источниках: 28 мая 2015 г.

Работа с тезисами доклада

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1. MISM.pdf MISM.pdf 1,2 МБ 22 марта 2016 [mkupr]

[1] Role of normal interlayer in ferromagnetic josephson junctions / N. G. Pugach, D. M. Heim, M. Y. Kupriyanov et al. // Moscow International Symposium on Magnetism (MISM), 29 June – 3 July 2014, Moscow Book of Abstracts. — PrintLETO.ru Moscow, 2014. — P. 29. The coexistence and competition of ferromagnetic (F) and superconducting (S) ordering leads to a rich spectrum of unusual physical phenomena, intensively studied during the recent years. One of the consequences is the so-called π Josephson junction with phase shift π in the ground state. One or two insulating (I) barriers may be introduced at the SF interfaces as well, in order to enlarge the product Jc RN in the π-phase. Here Jc is the critical current density of the junction and RN is its normal resistance. Nowadays, the development of magnetic memory cells for rapid single flux quantum (RSFQ) logics becomes more and more actual. Only recently, a new type of magnetic memory element based on a junction with a complex ferromagnet-superconductor-insulator weak link (SIsFS) was proposed. One of the aims of our calculation is to study the behaviour of such SIsFS junctions when their middle superconducting layer is in the normal state. Introducing a normal metal (N) layer between the F layer and the S electrode into a ferromagnetic Josephson junction (FJJ) is technologically necessary. Such an additional N layer was used in many FJJs. However, it was not taken into account by any theoretical explanation of these experiments [1]. We calculate the critical current density Jc of FJJs containing ferromagnetic, normal, and insulating layers in the weak link region. We determine the Green's functions with the help of the Usadel equations, which we use in theta parametrization. The Kupriyanov-Lukichev boundary conditions at all interfaces were used. It was shown earlier that insulating barriers decrease the critical current density and shift the 0-π transitions to smaller values of the ferromagnet thickness dF [2,3]. A thin N layer inserted between S and I layers does not significantly influence the Josephson effect. However, if the N layer is inserted between I and F layers, it can have a large effect on the Josephson current. The presence of the N layer may increase the amplitude of Jc(dF) and shift the first 0-π transition to larger dF. The oscillation period of Jc(dF) is still determined by the relation of the magnetic exchange energy H and the diffusion coefficient in the dirty limit. It is shown that even a thin additional N layer may change the boundary conditions at the IF boundary depending on the value of its conductivity. We conclude that it effectively mitigates the effect of the insulating barrier on the decaying oscillations of the critical current density Jc(dF). Even technological thin N layers, which almost do not suppress the superconducting correlation, have to be taken into account for the explanation of experimental results concerning the Josephson effect in FJJs. For example, the 0 and π states of multilayered FJJs containing few normal layers, proposed recently as basis for a cryogenic magnetic memory, should be determined very carefully. Using the developed approach we explain the existing experiments on SIFS and SINFS FJJs [1]. Support by RFBR (13-02-01452, 14-02-91350), SFB-TRR21, EP/J010618/1 is acknowledged. [1] M. Weides, M. Kemmler, E. Goldobin, et.al. Appl. Phys. Lett. 89, 122511 (2006). [2] A. S. Vasenko, A. A. Golubov, M. Y. Kupriyanov, et. al. Phys. Rev. B 77, 134507 (2008). [3] A. Buzdin, JETP Lett. 78, 1073 (2003).

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