Beyond ferromagnetic spintronics: antiferromagnetic I-Mn-V semiconductors Tomas Jungwirth Institute of Physics in Prague & University of Nottingham.

Beyond ferromagnetic spintronics: antiferromagnetic I-Mn-V semiconductors

Tomas JungwirthInstitute of Physics in Prague & University of Nottingham

Kvantová relativistická fyzika

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),(

2

2

22

2

trrm

trt

i

m

pE

Spintronics ← relativistic quantum physics

Kvantová relativistická fyzika

)/1(/1

,

22

02

cv

mmmcE

Spintronics ← relativistic quantum physics

Kvantová relativistická fyzika

Spintronics ← relativistic quantum physics

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Ultra-relativistic particles with spin (neutrino): spcE

Spin-orbit coupling

Weaker but also present in electrons in solids

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

Bm ||

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

Bm ||

... and memory

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

Bm ||

Lord Kelvin 1857

First spintronic devicesPoor scalability to small dimensions & small MR (subtle spin-orbit origin)

Current spintrnic devicesInterface effect → nanoscale in nature& large MR (robust ferromagnetic origin)

Fert, Grünberg et al. 1988

Bulk AMR TMR (GMR)

Spintronic magnetoresistance effects in metals

HDD read-head sensors

Magnetic RAM

)()()( 2mRmRmR

)()()( mRmRmR

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

Wunderlich, Irvine, Jungwirth et al. PRL’06, Schlapps, Weiss et al. PRB’09

Electrical control of spintronics

B (T) → rotating m→

VG1

VG2

Positive & negative MR

Spintronic control of electronics

m1→

m2

→

p-type & n-type transistor

(m)→

(Ga,Mn)As

(Ga,Mn)As

...FM at huge dopings > 1% (> 1020 cm-3 )→ more of a low-density metallic alloy

Tc below room-T ( 190K)

Novák, Jungwirth et al. PRL ’08

Limitations of ferromagnetic semiconductor (Ga,Mn)As

Tc

Well behaved Itinerant ferromagnet but...

Shick, Jungwirth et al. ‘06Wunderlich, Jungwirth, Shick et al. ’06

Bernand-Mantel, Fert et al. ‘09

Theory predictions

Confirmed by experimentsGao, Tsumbal, Parkin et al. ’07Park,Wunderlich, Jungwirth et al. 08

AMR-type effects predicted and observed in high-Tc FM metal nanostructures

cobaltPtAlOx

Pt/Co

spontaneous moment

spin

-orb

it cou

plin

g

FM AFM

Shick , Wunderlich, Jungwirth, et al., PRB‘10

Magnetic and magneto-transport anisotropy effects present in AFMs with spin-orbit equally well as in FMs

Maximizing the anisotropy phenomena in metals → spintronics in the AFMs

AFM metal AFM metal MMnIrnIr

)( 2mR

Much easier to realize strong AFM-SC than FM-SC

Can AFMs resolve the problem of high-T SEMICONDUCTOR spintronics?

Jungwirth, Novak, et al., preprint ‘10

EFermiEgap

Eexchange

Eexchange competing with Egap in FM-SCs

No Eexchange competing with Egap in AFM-SCs

Strong FM exchange spitting turns the system into metal

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

Si

Si

2 group-IV Si per elementary cell → 8 (sp) valence electrons

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

IV: no magnetic SC analogue

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

Si

Si

1 proton transfer

IV III-V

IV: no magnetic SC analogue

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

Magnetic SCs derived from common 8-valence non-magnetic SCs

III-V: FeAs – SC, AFM TN=77K GdN – SC, FM Tc=72K (Ga,Mn)As – low-density metal, FM Tc<190K

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

IV: no magnetic SC analogue

Lower moment Fe (Gd) less favorable than high moment Mn → II-VI intrinsic magnetic SCs

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

Magnetic SCs derived from common 8-valence non-magnetic SCs

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

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 Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

II-VI: MnO, MnS, MnSe, MnTe - SC, AFM TN ~ 100 - 300K EuO, EuS – SC, FM Tc<70K EuSe, EuTe - SC, AFM TN<10K

All III-V and II-VI magnetic SCs have low transition-T

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

IV: no magnetic SC analogue

Larger more ionic bonds weaken magnetic interactions in II-V‘s

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

Can we make high moment (Mn) and smaller lattice (pnictides) intrinsic SC?

III-V: FeAs – SC, AFM TN=77K GdN – SC, FM Tc=72K (Ga,Mn)As – low-density metal, FM Tc<190K

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

I(AM) Li, Na,..

(TM) Cu, Ag, ..

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

I(AM) Li, Na,..

(TM) Cu, Ag, ..I-II-V: LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM TN >> room T

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

Bronger et al., Z. among. allg. Chem. ’86

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

I(AM) Li, Na,..

(TM) Cu, Ag, ..

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

III-V I-II-V

Twin SCs

I-Mn-VBronger et al., Z. among. allg. Chem. ’86

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

I-II-V: LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM TN >> room T

II Zn, Cd, ..

IIIAl, Ga, ..

IVSi, Ge, ..

V (pnictides)

N, P, As, ..

VI (chalcogenides)

O, S, Se, Te, ..

I(AM) Li, Na,..

(TM) Cu, Ag, ..

Mn (d5 s2) Fe

Eu (f7 s2) Gd

II III

I-Mn-V

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?

Bronger et al., Z. among. allg. Chem. ’86

Magnetic (FM & AFM) SCs derived from common 8-valence non-magnetic SCs

I-II-V: LiMnAs, NaMnAs, LiMnP, LiMnSb... - AFM TN >> room T

InAs

LiMnAsMBE growth of I-Mn-V:

LiMnAs on nearly lattice matched InAs

4.27A

4.28A

[110] [-110]LiMnAs

MnAs

grow

th d

rect

ion

log(intensity)

200

0

400 600 800

100

200

x (m)

prof

ile

(nm

)

wavelength (nm)1000 1200 1400

LiMnAs

InAs cap

substrate

LiMnAs

In situ RHEED In situ optical reflectivity

Ex situ profile

Sharp 2D cubic single-crystal growth

... poor growth of control umatched MnAs

Fabry-Perot oscillations → semiconductor

5.3

2~

log(

inte

nsit

y)

X-ray diffraction

All LiMnAs crystal peaks observed

Fully tensile strained on InAs(0.2% increase of LiMnAs volume)

InAs

LiMnAs

4.27A

4.28A

Expected 45o rotation of LiMnAs with respect to the InAs substrateInAs

LiMnAs

[110]LiMnAs

InAs [100]

X-ray diffraction

M

(104 e

mu)

H (T)

MnAs

Mn S=5/2

LiMnAs

energy (meV)

I T/I

0

InAs

Li:InAs

LiMnAs

MnAs

temperature (K)

Mre

m

(104 e

mu)

LiMnAs

MnAs

Ex situ optical transmission Squid magnetization

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

Ab initio theory

Stoichiometric I-Mn-V are strong AFMs & intrinsic semiconductors

Magnetic and correlated Mn d-states mixed near band gap

→ low √ (refractive index), strong and gatable magnetic anisotropy effects

LDA

AFM semiconductors for spintronics

AFM

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

FM

AFM semiconductors for spintronics

2. Exchange-biasing AFM with embeded conventional semiconductor devices

Fixed by exchange-biasing AFM

Transistor directly in the AFM layer

Opto-electronics directly in the AFM layer

Discrete spintronic and transistor elements in current MRAM

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

Conclusions

Prospect for high-T semiconductor spintronics but first sytematic materials research needs to be completed

University of NottinghamTom Foxon, Richard Campion,

Bryan Gallagher, et al.

Hitachi & Cavendish Laboratories at CambridgeJorg Wunderlich, Andrew Irvine et al.

Institute of Physics ASCR, PragueVít Novák, Miroslav Cukr , Jan Mašek, Alexander

Shick, František Máca,Petr Kužel, et al.

Charles University, PragueXavi Marti, Petra Horodyská, Václav Holý, Petr Němec, et al.

Texas A&M and University of TexasJairo Sinova, Allan MacDonald, et al.