Spin valve effects in superconductor/ferromagnetic devices

1
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

2
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.
Outline
3
Peculiarities of proximity effect at SF
interfaces. (Long range proximity effect).
even in momentum and odd in frequency
4
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.

5
Control of Tc due to oscillatory character of
singlet and short range triplet correlation.
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., Pisma
ZhETP, 90, 149, 2009. V.I. Zdravkov, J. Kehrle et
al., PRB 2009 accepted for publication
L.R.T., Physica C (1998)M.G. Khusainov, Yu.N.
Proshin, PRB (1997)
6
Superconducting short range spin valve (SSRSV)
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)
7
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)
8
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)
9
Josephson spin valves (theoretical suggestions)
10
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.
11
The proposed solutions

• To govern the induced superconductivity rather
  than self-superconductivity.
• To increase of x1 and x2 by shifting from ? to
  ?eff

T. Yu. Karminskaya and M. Yu. Kupriyanov, Pisma
Zh. Eksp.Teor. Fiz. 85, 343 (2007) JETP Lett.
85, 286 (2007). T. Yu. Karminskaya and M. Yu.
Kupriyanov, Pisma Zh. Eksp.Teor. Fiz. 86, 65
(2007) JETP Lett. 86, 61 (2007_). T. Yu.
Karminskaya M. Yu. Kupriyanov and A.A.Golubov,
Pisma Zh. Eksp.Teor. Fiz. 87, 657 (2008) JETP
Lett. 87, 570 (2008).
12
Dependence of critical current components as a
function of distance between superconducting
electrodes
13
In S-(FNF)-S Josephson junctions it is possible
not only to increase ?F1 and ?F2 up to the scale
of ?N, but also to control both the value and
the sign of critical current by changing the
direction of magnetization of a F layer.
L/?N 0.1 (0 - 0)
L/?N 1 (p - 0 )
14
Deviation of F film magnetization vector from
antiferromagnetic configuration is the more
effective way for the critical current control.
15
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.
16
Dependence of critical current components as a
function of distance between superconducting
electrodes
17
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.

18
S-NF-S junctions with arbitrary values of N and F
films thickness and transport properties of NF
interface.
19
Expression for the critical current
20
Dependence of the wave vector on thickness of the
F layer
21
Dependence of the wave vector on suppression
parameter gB at FN interface
22
Thickness dependence of the critical current
23
Dependence of the critical current on distance
between S electrodes
24
Dependence of the critical current on thickness
of F film
25
The Ic(L,dF) phase diagram
26
Ic magnitude as a function of distance between S
electrodes for different geometry of S-NF-S
Josephson junctions
27
Ic magnitude as a function of length of weak link
region located under S electrodes for different
geometry of S-NF-S Josephson junctions
28
Ic magnitude as a function of length of weak link
region located under S electrodes for different
geometry of S-NF-S Josephson junctions
29
Josephson junctions with controlled Tc of S
electrode
30
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.
31

• Thank you for your attention.

32
?????????????? ?????????? ??????
33
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.
34
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
35
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).
36
Dependence of fundamental wave vectors upon ratio
of coupling coefficients between N and F films
37
(No Transcript)
38
(No Transcript)
39
Characteristic lengths in ferromagnetic materials
for SFS Josephson junctions.