Spin valve effects in
superconductor/ferromagnetic devices
M.Yu.Kupriyanov,
Institute of Nuclear Physics Moscow State University, Moscow, Russia
R. G. Deminov
Physics Faculty, Kazan State University, 420008 Kazan, Russia
Ya. V. Fominov
L. 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
Outline
1. Present experimental status and the main difficulties in
practical realization of superconductor spintronic devices.
2. S-(NF)-S and S-(FNF)-S Josephson junctions as the
solution of the problems.
3. S-(FNF)-S structures as a novel building block of
Josephson spintronics.
4. Conclusion.
Peculiarities of proximity effect at SF interfaces.
(Long range proximity effect).
even in
momentum
and odd
in
frequency
Spin 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
singlet and short range triplet correlation.
Re-entrant superconductivity
in superconductor-ferromagnet
Experimental observation of the re-entrant
superconductivity and double suppression of
bilayers (theory)
superconductivity in the Nb/Cu41Ni59 bilayers
L.R.T., Physica C (1998)
M.G. Khusainov, Yu.N. Proshin, PRB (1997)
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
Superconducting short range spin valve
(SSRSV)
N
SP
SAP
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 long range spin valve
(SLRSV)
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)
Superconducting long range spin valve
(SLRSV)
Idea: S. Oh, D. Youm and M.R. Beasley, APL 71, 2376 (1997).
Implementation: I.A. Garifullin, P.V. Leksin et al. (unpublished)
1.0
H= - 50 Oe
R/R(Tc)
0.8
0.6
b
0.4
0.2
0.0
1.50
H= + 50 Oe
1.75
2.00
2.25
T, K
2.50
2.75
Josephson spin valves (theoretical suggestions)
The main difficulties in practical realization of
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 solutions
• To govern the induced superconductivity
rather than self-superconductivity.
• To increase of x1 and x2 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
function of distance between superconducting
electrodes
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)
I c   3I c 
L/ξN = 1 (p - 0 )
I c   7 I c 
Deviation of F film magnetization vector from
antiferromagnetic configuration is the more effective way
for the critical current control.
Fundamental wave vectors.
There is generation of long range triplet component in the
vicinity of angles around p .
It falls down slowly than the singlet one.
Dependence of critical current components as a function of
distance between superconducting electrodes
Limitations
• All conclusions have been made under the
following limitations
• 1. Thickness of F and N layers are small in
the scale of xN and xF, respectively.
• 2. The transparency of SF interface must not
be too small.
S-NF-S junctions with arbitrary values of N
and F films thickness and transport
properties of NF interface.
Expression for the critical current
Dependence of the wave vector on
thickness of the F layer
Dependence of the wave vector on
suppression parameter gB at FN interface
Thickness dependence of the critical current
Dependence of the critical current on
distance between S electrodes
Dependence of the critical current on
thickness of F film
The Ic(L,dF) phase diagram
Ic magnitude as a function of distance between S electrodes
for different geometry of S-NF-S Josephson junctions
Ic magnitude as a function of length of weak link region located
under S electrodes for different geometry of S-NF-S Josephson
junctions
Ic magnitude as a function of length of weak link region located
under S electrodes for different geometry of S-NF-S Josephson
junctions
Josephson junctions with controlled Tc of S electrode
Conclusion
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.
Математическая постановка задачи
Conclusion
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.
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.
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.
Present experimental status and the main difficulties in
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?
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
coupling coefficients between N and F films
Characteristic lengths in ferromagnetic materials
for SFS Josephson junctions.
Table.1 Characteristic lengths in ferromagnetic materials for SFS Josephson junctions.
Ref.
C. Bell, R. Loloee, G. Burnell, and M. G. Blamire Phys. Rev.
B 71, 180501 (R) 2005
J. W. A. Robinson, S. Piano, G. Burnell, C. Bell, and M. G.
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This work
J. W. A. Robinson, S. Piano, G. Burnell, C. Bell, and M. G.
Blamire, Critical Current Oscillations in Strong Ferromagnetic
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ξ1
(nm)
1,2
ξ2
(nm)
1,6
F- material
Fe20Ni80
2.2 105
1100
1,4
0,46
Fe20Ni80
2.2 105
2300
1,8
2
Pd0.9Ni0.1
2 105
400
1,3
3,5
Cu0.53Ni0.47
vF (m/c)
H (K)
850
Cu0.52Ni0.48
1,7
1
Ni
2.8 105
2300
4,1
1,2
Ni
2.8 105
1000
4,6
3,0
0,45
0,3
Ni3Al
Co
1.5 105
2.8 105
1000
3500