Transcript Slide 1

Beyond ferromagnetic spintronics:
antiferromagnetic I-Mn-V semiconductors
Tomas Jungwirth
Institute of Physics in Prague & University of Nottingham
Spintronics ← relativistic quantum physics
Kvantová relativistická fyzika
p2
E 
2m


i
 (r , t ) 
t

2 2

 (r , t )
2m r 2
Spintronics ← relativistic quantum physics
Kvantová relativistická fyzika
E  m c , m  m0
2
  1 / (1  v / c )
2
2
Spintronics ← relativistic quantum physics
Kvantová relativistická fyzika
Spin-orbit coupling
}
}
Ultra-relativistic particles with spin (neutrino):
Weaker but also present in electrons in solids
 
E  cp  s
Electron has spin & charge → magnetic moment
| m |  B
Collective behavior of spins due to Coulomb interaction → magnetism
Provides sensitivity to weak external fields & yields strong electrical signals
Electron has spin & charge → magnetic moment
| m |  B
Collective behavior of spins due to Coulomb interaction → magnetism
Provides sensitivity to weak external fields & yields strong electrical signals
Electron has spin & charge → magnetic moment
| m |  B
Collective behavior of spins due to Coulomb interaction → magnetism
Provides sensitivity to weak external fields & yields strong electrical signals
... and memory
Spintronic magnetoresistance effects in metals
Bulk AMR
TMR (GMR)
Lord Kelvin 1857
Fert, Grünberg et al. 1988
Magnetic RAM
HDD read-head sensors


2
R(m)  R(m)  R(m )
First spintronic devices
Poor scalability to small dimensions
& small MR (subtle spin-orbit origin)



R(m)  R(m)  R(m)
Current spintrnic devices
Interface effect → nanoscale in nature
& large MR (robust ferromagnetic origin)
Towards semiconductor spintronics
FM semiconductors
Ohno et al. Science’98, Dietl et al PRB’00, Jungwirth, MacDonald et al PRB’99
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
Huge (~1000%) AMR-type effects in (Ga,Mn)As nanostructures
→
(m)
Electrical control of spintronics
Positive & negative MR
VG1
VG2
→
B (T) → rotating m
Spintronic control of electronics
p-type & n-type transistor
→
m1
Wunderlich, Irvine, Jungwirth et al.
PRL’06, Schlapps, Weiss et al. PRB’09
→
m2
Limitations of ferromagnetic semiconductor (Ga,Mn)As
Well behaved Itinerant ferromagnet but...
(Ga,Mn)As
...FM at huge dopings > 1% (> 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
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
Pt
AlOx
Pt/Co
cobalt
Maximizing the anisotropy phenomena in metals → spintronics in the AFMs
AFM metal MnIr
spontaneous moment
spin-orbit coupling
FM
AFM
2
 R( m ) 
Magnetic and magneto-transport anisotropy effects present in AFMs with
spin-orbit equally well as in FMs
Shick , Wunderlich, Jungwirth, et al., PRB‘10
Can AFMs resolve the problem of high-T SEMICONDUCTOR spintronics?
Jungwirth, Novak, et al., preprint ‘10
Eexchange competing with Egap
in FM-SCs
No Eexchange competing with Egap in
AFM-SCs
Eexchange
Egap
Strong FM exchange spitting
turns the system into metal
EFermi
Much easier to realize strong
AFM-SC than FM-SC
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
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
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
IV: no magnetic SC analogue
O, S, Se, Te, ..
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
IV: no magnetic SC analogue
1 proton transfer
IV
Si
Si
III-V
Magnetic SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
IV: no magnetic SC analogue
III-V: FeAs – SC, AFM TN=77K
GdN – SC, FM Tc=72K
(Ga,Mn)As – low-density metal, FM Tc<190K
Lower moment Fe (Gd) less favorable than high moment Mn → II-VI intrinsic magnetic SCs
Magnetic SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
IV: no magnetic SC analogue
III-V: FeAs – SC, AFM TN=77K
GdN – SC, FM Tc=72K
(Ga,Mn)As – low-density metal, FM Tc<190K
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
IV: no magnetic SC analogue
III-V: FeAs – SC, AFM TN=77K
GdN – SC, FM Tc=72K
(Ga,Mn)As – low-density metal, FM Tc<190K
II-VI: MnO, MnS, MnSe, MnTe - SC, AFM TN ~ 100 - 300K
EuO, EuS – SC, FM Tc<70K
EuSe, EuTe - SC, AFM TN<10K
Larger more ionic bonds weaken magnetic interactions in II-V‘s
All III-V and II-VI magnetic SCs have low transition-T
Can we make high moment (Mn) and smaller lattice (pnictides) intrinsic SC?
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
I
(AM) Li, Na,..
(TM) Cu, Ag, ..
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
(TM) Cu, Ag, ..
I-II-V: LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM TN >> room T
Bronger et al., Z. among. allg. Chem. ’86
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
(TM) Cu, Ag, ..
I-II-V: LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM TN >> room T
Bronger et al., Z. among. allg. Chem. ’86
III-V
I-II-V
Twin SCs
I-Mn-V
Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs
II
III
Mn (d5 s2) Fe
Eu (f7 s2) Gd
II
III
IV
V (pnictides) VI (chalcogenides)
Zn, Cd, ..
Al, Ga, .. Si, Ge, .. N, P, As, ..
O, S, Se, Te, ..
I
(AM) Li, Na,..
(TM) Cu, Ag, ..
I-II-V: LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM TN >> room T
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?
I-Mn-V
MBE growth of I-Mn-V:
LiMnAs on nearly lattice matched InAs
Li MnAs
4.27A
4.28A
InAs
In situ RHEED
[110]
In situ optical
reflectivity
LiMnAs [-110]
InAs cap
MnAs
growth drection
log(intensity)
Sharp 2D cubic single-crystal growth
  3.5
 ~2
LiMnAs
1000
1400
1200
wavelength (nm)
Fabry-Perot oscillations → semiconductor
... poor growth of control umatched MnAs
profile (nm)
Ex situ profile
200
LiMnAs
100
substrate
0
200
x
400
(m)
600
800
X-ray diffraction
log(intensity)
Li MnAs
4.27A
All LiMnAs crystal peaks observed
4.28A
InAs
Fully tensile strained on InAs
(0.2% increase of LiMnAs volume)
Li MnAs
X-ray diffraction
LiMnAs [110]
InAs [100]
InAs
Expected 45o rotation of LiMnAs with
respect to the InAs substrate
Ex situ optical transmission
LiMnAs
Li:InAs
MnAs
Mrem (104 emu)
IT/I0
InAs
Squid magnetization
MnAs
LiMnAs
temperature (K)
energy (meV)
Transparent at least up to InAs band-gap
Magnetization consistent with compensated AFM
moments in LiMnAs upto studied 400K
MnAs
M (104 emu)
Consistent with in situ Febry-Perot oscillations
and compare with non-transparent metal MnAs
Mn S=5/2
LiMnAs
H (T)
Compare with FM MnAs with same amount of Mn
Ab initio theory
Stoichiometric I-Mn-V are strong AFMs & intrinsic semiconductors
LDA
Magnetic and correlated Mn d-states mixed near band gap
→ low √ (refractive index), strong and gatable magnetic anisotropy effects
AFM semiconductors for spintronics
1. Electrically gatable magnetic and magneto-transport anisotropy effects
FM
AFM
Feasible to rotate magnetic easy-axis electrically in high-doped (Ga,Mn)As
→ should be much more accessible in intrinsic SCs I-Mn-V
AFM semiconductors for spintronics
2. Exchange-biasing AFM with embeded conventional semiconductor devices
Fixed by exchangebiasing AFM
Transistor directly
in the AFM layer
Discrete spintronic and
transistor elements in
current MRAM
Opto-electronics directly
in the AFM layer
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
Institute of Physics ASCR, Prague
Vít Novák, Miroslav Cukr , Jan Mašek, Alexander
Shick, František Máca,Petr Kužel, et al.
University of Nottingham
Tom Foxon, Richard Campion,
Bryan Gallagher, et al.
Charles University, Prague
Xavi Marti, Petra Horodyská, Václav Holý, Petr Němec, et al.
Hitachi & Cavendish Laboratories at Cambridge
Jorg Wunderlich, Andrew Irvine et al.
Texas A&M and University of Texas
Jairo Sinova, Allan MacDonald, et al.