Spin valve effects in Spin valve effects in superconductor/ferromagnetic devicessuperconductor/ferromagnetic devices

M.Yu.Kupriyanov, Institute of Nuclear Physics Moscow State University, Moscow, Russia

R. G. DeminovPhysics Faculty, Kazan State University, 420008 Kazan, Russia

Ya. V. FominovL. D. Landau Institute for Theoretical Physics RAS, 117940 Moscow, Russia

• A. A. Golubov,• Faculty of Science and Technology and MESAInstitute of Nanotechnology, University of

Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

T. Yu. Karminskaya,Institute of Nuclear Physics Moscow State University, 119992, Moscow, Russia

• L. R. Tagirov• Physics Faculty, Kazan State University, 420008 Kazan, Russia

1. Present experimental status and the main difficulties in 1. Present experimental status and the main difficulties in practical realization of superconductor spintronic devices. practical realization of superconductor spintronic devices. 2. S-(NF)-S and S-(FNF)-S Josephson junctions as the 2. S-(NF)-S and S-(FNF)-S Josephson junctions as the solution of the problems.solution of the problems.3. S-(FNF)-S structures as a novel building block of 3. S-(FNF)-S structures as a novel building block of Josephson spintronics. Josephson spintronics.

4. Conclusion.4. Conclusion.

Outline

Peculiarities of proximity effect at SF interfaces.Peculiarities of proximity effect at SF interfaces. (Long range proximity effect).(Long range proximity effect).

even in momentum and odd in frequency

Spin valve devicesSpin valve devices

• 1. Control of Tc due to oscillatory character of singlet and short range triplet correlation.

• 2. Control of Tc by switching on or off long range triplet correlation.

• 3. Control of Jc of Josephson junctions due to oscillatory character of singlet and short range triplet correlation.

• 4. Control of Jc of Josephson junctions by switching on or off long range triplet correlation.

Control of Tc due to oscillatory character of Control of Tc due to oscillatory character of singlet and short range triplet correlation.singlet and short range triplet correlation.

L.R.T., Physica C (1998)M.G. Khusainov, Yu.N. Proshin, PRB (1997)

Re-entrant superconductivity

in superconductor-ferromagnet

bilayers (theory)

Experimental observation of the re-entrant superconductivity and double suppression of

superconductivity in the Nb/Cu41Ni59 bilayers

V.I. Zdravkov, A.S. Sidorenko et al., PRL 97, 057004, 2006. A. S. Sidorenko, et al., Pis’ma ZhETP, 90, 149, 2009.V.I. Zdravkov, J. Kehrle et al., PRB 2009 – accepted for publication

SP SAP

N

L. R. T., PRL 83, 2058 (1999); A. I. Buzdin et al., EPL 48, 686 (1999).Ya. V. Fominov, N. M. Chtchelkatchev, and A. A. Golubov, PRB 66, 014507 (2002).A.F. Volkov, F.S. Bergeret and K.B. Efetov, PRL 90, 117006 (2003);Ya.V. Fominov, A. A. Golubov, and M. Yu. Kupriyanov, JETPL 77, 510 (2003)

Superconducting short range spin valveSuperconducting short range spin valve ((SSRSVSSRSV))

Superconducting long range spin valveSuperconducting long range spin valve ((SLRSVSLRSV))

G. Nowak, H. Zabel et al, Phys. Rev. B 78, 134520 2008

T.Yu. Karminskaya, Ya.V. Fominov, A.A. Golubov, M.Yu. Kupriyanov, R.G. Deminov, L.R. Tagirov (unpublished)

Idea: S. Oh, D. Youm and M.R. Beasley, APL 71, 2376 (1997).Implementation: I.A. Garifullin, P.V. Leksin et al. (unpublished)

1.50 1.75 2.00 2.25 2.50 2.75

0.0

0.2

0.4

0.6

0.8

1.0

H= - 50 Oe

R/R

(Tc)

T, K

H= + 50 Oe

b

Superconducting long range spin valveSuperconducting long range spin valve ((SLRSVSLRSV))

Josephson spin valves (theoretical suggestions)Josephson spin valves (theoretical suggestions)

The main difficulties in practical realization of The main difficulties in practical realization of superconductor spintronic devices.superconductor spintronic devices.

1. The decay length and period of Ic oscillations are in nanometer scale.

2. These lengths are comparable with the dead layer thickness at SF interfaces.

3. There are difficulties in changing of orientation of F layers magnetization vectors in SFIFS devices.

4. Contradictoriness of the demands to S layer thickness in FSF control units.

The proposed solutionsThe proposed solutions

• To govern the induced superconductivity rather than self-superconductivity.

• To increase of and by shifting from Н to Нeff

T. Yu. Karminskaya and M. Yu. Kupriyanov, Pis’ma Zh. Eksp.Teor. Fiz. 85, 343 (2007) [JETP Lett. 85, 286 (2007)].T. Yu. Karminskaya and M. Yu. Kupriyanov, Pis’ma Zh. Eksp.Teor. Fiz. 86, 65 (2007) [JETP Lett. 86, 61 (2007_)].T. Yu. Karminskaya M. Yu. Kupriyanov and A.A.Golubov, Pis’ma Zh. Eksp.Teor. Fiz. 87, 657 (2008) [JETP Lett. 87, 570 (2008)].

Dependence of critical current components as a Dependence of critical current components as a function of distance between superconducting function of distance between superconducting

electrodeselectrodes

In S-(FNF)-S Josephson junctions it is possible not only to increase ξF1 and ξF2 up to the scale of ξN, but also to control both the value and the sign of critical current by changing the direction of magnetization of a F layer.

L/ξN = 0.1 (0 - 0) cc II 3

L/ξN = 1 ( - 0 ) cc II 7

Deviation of F film magnetization vectorDeviation of F film magnetization vector from from antiferromagnetic configuration is the more effective way antiferromagnetic configuration is the more effective way

for the critical current control. for the critical current control.

Fundamental wave vectors. Fundamental wave vectors. There is generation of long range triplet component in the There is generation of long range triplet component in the

vicinity of angles around vicinity of angles around . .

It falls down slowly than the singlet oneIt falls down slowly than the singlet one . .

Dependence of critical current components as a function of Dependence of critical current components as a function of distance between superconducting electrodesdistance between superconducting electrodes

LimitationsLimitations

• All conclusions have been made under the following limitations

• 1. Thickness of F and N layers are small in the scale of N and F, respectively.

• 2. The transparency of SF interface must not be too small.

S-NF-S junctions with arbitrary values of N S-NF-S junctions with arbitrary values of N and F films thickness and transport and F films thickness and transport

properties of NF interface.properties of NF interface.

Expression for the critical currentExpression for the critical current

Dependence of the wave vector on Dependence of the wave vector on thickness of the F layerthickness of the F layer

Dependence of the wave vector on Dependence of the wave vector on suppression parameter suppression parameter at FN interfaceat FN interface

Thickness dependence of the critical Thickness dependence of the critical currentcurrent

Dependence of the critical current on Dependence of the critical current on distance between S electrodesdistance between S electrodes

Dependence of the critical current on Dependence of the critical current on thickness of F filmthickness of F film

The The IIcc((LL,,ddFF) phase diagram) phase diagram

IIcc magnitude as a function of distance between S electrodes magnitude as a function of distance between S electrodes

for different geometry of S-NF-S Josephson junctionsfor different geometry of S-NF-S Josephson junctions

IIcc magnitude as a function of length of weak link region located magnitude as a function of length of weak link region located

under S electrodes for different geometry of S-NF-S Josephson under S electrodes for different geometry of S-NF-S Josephson junctionsjunctions

IIcc magnitude as a function of length of weak link region located magnitude as a function of length of weak link region located

under S electrodes for different geometry of S-NF-S Josephsonunder S electrodes for different geometry of S-NF-S Josephson junctionsjunctions

Josephson junctionsJosephson junctions with controlledwith controlled Tc of S electrodeTc of S electrode

ConclusionConclusion

We believe that the suggested S-FNF-S Josephson devices opens the way for transformation of the problem of interaction of

superconductivity and ferromagnetism from pure fundamental to more practically oriented.

- there is no anymore serious limitations on the distance between superconducting electrodes;

- the quality of SF interfaces, as well as the problem of dead layer is not important;

- the magnitude and sign of the critical current are very robust against a deviation of F and N layers thickness and quality of SF interfaces.

- the suggested FNF control unit may be also used for control of critical temperature of superconducting films, as well as Jc of Josephson structures.

• Thank you for your attention.Thank you for your attention.

Математическая постановка задачиМатематическая постановка задачи

ConclusionConclusion

1. We have suggested the novel class of S-FN-S and S-FNF-S Josephson devices and have proven theoretically that it is possible to enhance in them the decay length and period of critical current oscillations up to the values (of the order of 100 nm), which are on one or two orders of magnitude larger compare to scale of these lengths having been achieved in recent experimental studies.

2. We have shown that FNF control unit in current in plane geometry is more effectively control the magnitude and sign of Josephson junction critical current rather than FIS and FSF elements in current out of plane geometry.

4. We have shown that the physics of this control lays in generation of long range triplet superconducting correlation, which decays into the weak link even slowly than usual singlet superconductivity.

3. It has been shown that the effective control over the magnitude and sign of IC of the structure is achieved at a small deflection of the vectors M1, 2 from the antiferromagnetic (M1 antiparallel to M2) configuration. This is in contrast to the all known spin valve devices, in which the main effect achieved as a result of switching from ferromagnetic to antiferromagnetic aliment of M1 and M2.

Present experimental status and the main difficulties in Present experimental status and the main difficulties in practical realization of superconductor spintronic devices.practical realization of superconductor spintronic devices.

V. I. Zdravkov, A. S. Sidorenko, et al. PRL 97, 057004, 2006

S. L. Prischepa, et al, Pisma Zh. Eksp. Teor. Fiz. 88, 431 (2008)

G. Nowak, H. Zabel et al, Phys. Rev. B 78, 134520 2008

What is the physics?What is the physics?

We have Heff instead of H. An electron for a certain time can be present in the N part of the FN film of the structure. This is equivalent to the subjection of electrons to the effective exchange energy averaged over the thickness of the FN film. This energy is obviously lower than the exchange energy in the ferromagnetic part of the structure.F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev.Lett. 86, 3140 (2001).Ya. V. Fominov, N. M. Chtchelkatchev, and A. A. Golubov,Phys. Rev. B 66, 014507 (2002).

Dependence of fundamental wave vectors upon ratio of Dependence of fundamental wave vectors upon ratio of coupling coefficients between N and F filmscoupling coefficients between N and F films

Characteristic lengths in ferromagnetic materials for SFS Josephson junctions.