Beyond ferromagnetic spintronics:

1
Beyond ferromagnetic spintronics
antiferromagnetic I-Mn-V semiconductors
Tomas Jungwirth
Institute of Physics in Prague University of
Nottingham
2
Spintronics ? relativistic quantum physics
Kvantová relativistická fyzika
3
Spintronics ? relativistic quantum physics
Kvantová relativistická fyzika
4
Spintronics ? relativistic quantum physics
Kvantová relativistická fyzika
5
Spin-orbit coupling
Ultra-relativistic particles with spin (neutrino)
Weaker but also present in electrons in solids
6
Electron has spin charge ? magnetic moment
Collective behavior of spins due to Coulomb
interaction ? magnetism Provides sensitivity to
weak external fields yields strong electrical
signals
7
Electron has spin charge ? magnetic moment
Collective behavior of spins due to Coulomb
interaction ? magnetism Provides sensitivity to
weak external fields yields strong electrical
signals
8
Electron has spin charge ? magnetic moment
Collective behavior of spins due to Coulomb
interaction ? magnetism Provides sensitivity to
weak external fields yields strong electrical
signals
... and memory
9
Spintronic magnetoresistance effects in metals
Bulk AMR
TMR (GMR)
Lord Kelvin 1857
Fert, Grünberg et al. 1988
Magnetic RAM
HDD read-head sensors
First spintronic devices Poor scalability to
small dimensions small MR (subtle spin-orbit
origin)
Current spintrnic devices Interface effect ?
nanoscale in nature large MR (robust
ferromagnetic origin)
10
Towards semiconductor spintronics
FM semiconductors
Ohno et al. Science98, Dietl et al PRB00,
Jungwirth, MacDonald et al PRB99
Archetypical material (Ga,Mn)As favorable FM
and spin-orbit coupled bands semiconductor
nano-fabrication ? revived interest in
spin-orbit phenomena like AMR in nanostructures
11
Huge (1000) AMR-type effects in (Ga,Mn)As
nanostructures
Wunderlich, Irvine, Jungwirth et al. PRL06,
Schlapps, Weiss et al. PRB09
12
Limitations of ferromagnetic semiconductor
(Ga,Mn)As
Well behaved Itinerant ferromagnet but...
(Ga,Mn)As
...FM at huge dopings gt 1 (gt 1020 cm-3 ) ?
more of a low-density metallic alloy Tc
below room-T (? 190K)
(Ga,Mn)As
Tc
Novák, Jungwirth et al. PRL 08
13
AMR-type effects predicted and observed in
high-Tc FM metal nanostructures
Theory predictions
Shick, Jungwirth et al. 06 Wunderlich,
Jungwirth, Shick et al. 06
Confirmed by experiments
Gao, Tsumbal, Parkin et al. 07 Park,Wunderlich,
Jungwirth et al. 08
Bernand-Mantel, Fert et al. 09
cobalt
14
Maximizing the anisotropy phenomena in metals ?
spintronics in the AFMs
AFM metal MnIr
FM
AFM
Magnetic and magneto-transport anisotropy effects
present in AFMs with spin-orbit equally well as
in FMs
Shick , Wunderlich, Jungwirth, et al., PRB10
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Can AFMs resolve the problem of high-T
SEMICONDUCTOR spintronics?
Jungwirth, Novak, et al., preprint 10
Much easier to realize strong AFM-SC than FM-SC
Strong FM exchange spitting turns the system into
metal
16
Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
Si
Si
2 group-IV Si per elementary cell ? 8 (sp)
valence electrons
17
Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
IV no magnetic SC analogue
18
Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
IV no magnetic SC analogue
19
Magnetic SCs derived from common 8-valence
non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
IV no magnetic SC analogue
III-V FeAs SC, AFM TN77K GdN SC,
FM Tc72K (Ga,Mn)As low-density metal,
FM Tclt190K
Lower moment Fe (Gd) less favorable than high
moment Mn ? II-VI intrinsic magnetic SCs
20
Magnetic SCs derived from common 8-valence
non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
IV no magnetic SC analogue
III-V FeAs SC, AFM TN77K GdN SC,
FM Tc72K (Ga,Mn)As low-density metal,
FM Tclt190K
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Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
IV no magnetic SC analogue
III-V FeAs SC, AFM TN77K GdN SC,
FM Tc72K (Ga,Mn)As low-density metal,
FM Tclt190K
II-VI MnO, MnS, MnSe, MnTe - SC, AFM TN 100 -
300K EuO, EuS SC, FM Tclt70K
EuSe, EuTe - SC, AFM TNlt10K
Larger more ionic bonds weaken magnetic
interactions in II-Vs
All III-V and II-VI magnetic SCs have low
transition-T
Can we make high moment (Mn) and smaller lattice
(pnictides) intrinsic SC?
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Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
(TM) Cu, Ag, ..
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Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
I-II-V LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM
TN gtgt room T
(TM) Cu, Ag, ..
Bronger et al., Z. among. allg. Chem. 86
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Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
I-II-V LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM
TN gtgt room T
(TM) Cu, Ag, ..
I-Mn-V
Bronger et al., Z. among. allg. Chem. 86
III-V
I-II-V
Twin SCs
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Magnetic (FM AFM) SCs derived from common
8-valence non-magnetic SCs
II
III
Mn (d5 s2)
II
III
IV
V (pnictides)
VI (chalcogenides)
Fe
Eu (f7 s2)
Gd
Zn, Cd, ..
Al, Ga, ..
Si, Ge, ..
N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
I-II-V LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM
TN gtgt room T
(TM) Cu, Ag, ..
I-Mn-V
Bronger et al., Z. among. allg. Chem. 86
No report on electronic structure of AFM I-Mn-V
Are they SCs? No report on MBE growth of
group-I compounds Can they be grown as
single-crystal epilayers?
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MBE growth of I-Mn-V LiMnAs on nearly lattice
matched InAs
Li
Mn
As
4.27A
4.28A
In
As
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In situ RHEED
In situ optical reflectivity
LiMnAs
110
-110
InAs cap
growth drection
log(intensity)
Sharp 2D cubic single-crystal growth
LiMnAs
MnAs
1000
1200
1400
wavelength (nm)
Fabry-Perot oscillations ? semiconductor
Ex situ profile
LiMnAs
... poor growth of control umatched MnAs
substrate
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X-ray diffraction
Li
Mn
As
4.27A
All LiMnAs crystal peaks observed
4.28A
In
As
Fully tensile strained on InAs (0.2 increase of
LiMnAs volume)
29
X-ray diffraction
Li
Mn
As
Expected 45o rotation of LiMnAs with respect to
the InAs substrate
In
As
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Ex situ optical transmission
Squid magnetization
MnAs
Mrem (104 emu)
LiMnAs
temperature (K)
Transparent at least up to InAs
band-gap Consistent with in situ Febry-Perot
oscillations and compare with non-transparent
metal MnAs Magnetization consistent with
compensated AFM moments in LiMnAs upto studied
400K Compare with FM MnAs with same amount of Mn
MnAs
Mn S5/2
M (104 emu)
LiMnAs
H (T)
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Ab initio theory
Stoichiometric I-Mn-V are strong AFMs intrinsic
semiconductors
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LDA
Magnetic and correlated Mn d-states mixed near
band gap ? low v? (refractive index), strong
and gatable magnetic anisotropy effects
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AFM semiconductors for spintronics
1. Electrically gatable magnetic and
magneto-transport anisotropy effects
Feasible to rotate magnetic easy-axis
electrically in high-doped (Ga,Mn)As ? should be
much more accessible in intrinsic SCs I-Mn-V
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AFM semiconductors for spintronics
2. Exchange-biasing AFM with embeded conventional
semiconductor devices
Discrete spintronic and transistor elements in
current MRAM
Fixed by exchange-biasing AFM
Transistor directly in the AFM layer
Opto-electronics directly in the AFM layer
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Conclusions

• FM SCs (GaMnAs) favorable model spintronic
  systems but low transition T
• AFM I-Mn-V compounds
• Simplest magnetic counterparts to conventional
  SCs with high transition T
• We showed that they are semiconductors and that
  the group-I alkali metal
• compounds can be grown by MBE as high quality
  single-crystal epilayers
• Admixture of magnetic d-states yields
  unconventional SC properties and
• theory predicts very strong and gatable
  spintronic responses

Prospect for high-T semiconductor spintronics but
first sytematic materials research needs to be
completed
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University of Nottingham Tom Foxon, Richard
Campion, Bryan Gallagher, et al.
Institute of Physics ASCR, Prague Vít Novák,
Miroslav Cukr , Jan Mašek, Alexander Shick,
František Máca,Petr Kužel, et al.
Charles University, Prague Xavi Marti, Petra
Horodyská, Václav Holý, Petr Nemec, et al.
Hitachi Cavendish Laboratories at
Cambridge Jorg Wunderlich, Andrew Irvine et al.
Texas AM and University of Texas Jairo Sinova,
Allan MacDonald, et al.
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