Jairo Sinova (TAMU) Making semiconductors magnetic: A new approach to engineering quantum materials NERC SWAN

Jairo Sinova (TAMU)

Making semiconductors magnetic: A new approach to engineering quantum materials

NERCSWAN

OUTLINE• DMS: intro to the phenomenology

– General picture– Theoretical approaches to DMSs

• Are we stuck with low Tc?– Intrinsic limits– Extrinsic limits– Strategies to increase Tc

• Impurity band and valence band in doped semicondcutors• Low doped insulating GaAs:Mn

– Activation energy: dc-transport and doping trends– Ac-conductivity and doping trends

• Impurity-band to disordered-valence-band crossover in highly-doped metallic GaAs:Mn– Dc-transport: lack of activation energy – Ac-conductivity– Red-shift of ac-conductivity mid-infrared peak in GaMnAs

• Other successful descriptions of system properties within the disordered-valence band treatment of metallic GaMnAs

– Tc trends vs substitutional Mn doping and carrier density; Magnetic anisotropy; Temperature dependence of transport in metallic samples, Magnetization dynamics; Domain wall dynamics and resistances; Anisotropic magnetoresistance; TAMR; Anomalous Hall effect

• Conclusions

Mn

Ga

AsMn

Ferromagnetic semiconductors

GaAs - GaAs - standard III-V semiconductorstandard III-V semiconductor

Group-II Group-II Mn - Mn - dilute dilute magneticmagnetic moments moments & holes& holes

(Ga,Mn)As - fe(Ga,Mn)As - ferrromagneticromagnetic semiconductorsemiconductor

More tricky than just hammering an iron nail in a silicon wafer

Mn

Ga

AsMn

Mn–hole spin-spin interaction

hybridization

Hybridization like-spin level repulsion Jpd SMn shole interaction

Mn-d

As-p

(Ga,Mn)As(Ga,Mn)As

5 d-electrons with L=0 S=5/2 local moment

intermediate acceptor (110 meV) hole

- Mn local moments too dilute (near-neighbours couple AF)

- Holes do not polarize in pure GaAs

- Hole mediated Mn-Mn FM coupling

Mn

Ga

AsMn

Ohno, Dietl et al. (1998,2000);Jungwirth, Sinova, Mašek, Kučera, MacDonald, Rev. Mod. Phys. (2006), http://unix12.fzu.cz/ms

Heff

= Jpd

<shole> || -x

MnAs

Ga

heff

= Jpd

<SMn> || x

Hole Fermi surfaces

Ferromagnetic Mn-Mn coupling mediated by holes

Technologically motivated and scientifically fueled

Incorporate magnetic properties with semiconductor

tunability (MRAM, etc)

Understanding complex phenomena:•Spherical cow of ferromagnetic systems (still very complicated)•Engineered control of collective phenomena•Benchmark for our understanding of strongly correlated systems

Generates new physics:•Tunneling AMR•Coulomb blockade AMR•Nanostructure magnetic anisotropy engineering

ENGINEERING OF QUANUTM MATERIALS

More knobs than usual in semiconductors: density, strain, chemistry/pressure, SO coupling engineering

Dilute moment nature of ferromagnetic semiconductors

GaAs Mn

Mn

10-100x smaller Ms

One

Current induced switchingreplacing external field Tsoi et al. PRL 98, Mayers Sci 99

Key problems with increasing MRAM capacity (bit density):

- Unintentional dipolar cross-links- External field addressing neighboring bits

10-100x weaker dipolar fields

10-100x smaller currents for switching

Sinova et al., PRB 04, Yamanouchi et al. Nature 04

GaMnAsAuAlOx Au

Tunneling anisotropic Tunneling anisotropic magnetoresistance (TAMR)magnetoresistance (TAMR)

Bistable memory device with a single magnetic layer only

Gould, Ruster, Jungwirth, et al., PRL '04

Giant magneto-resistance

(Tanaka and Higo, PRL '01)

[100]

[010]

[100]

[010]

[100]

[010]

Recently discovered in metals as well!

One

Dipolar-field-free current induced switching nanostructures

Micromagnetics (magnetic anisotropy) without dipolar fields (shape anisotropy)

~100 nm

(b)

Domain wall

Strain controlled magnetocrystalline (SO-induced) anisotropy

Can be moved by ~100x smaller currents than in metals

Humpfner et al. 06,Wunderlich et al. 06

Huge & tunable magnetoresistance in (Ga,Mn)As side-gated nano-constriction FET

Wunderlich, Jungwirth, Kaestner, Shick, et al., preprint

Single-electron Single-electron transistortransistor

Coulomb blockade anisotropic magnetoresistance

Band structure (group velocities, scattering rates, chemical potentialchemical potential) depend on M

Spin-orbit coupling

If lead and dot differentIf lead and dot different (different carrier concentrations in our (Ga,Mn)As SET)

Q

0

DL'

D' )M()M()M(&

e

)M(Q)Q(VdQU

GMMGG0

20

C

C

e

)M(V&)]M(VV[CQ&

C2

)QQ(U

electric && magneticmagneticcontrol of Coulomb blockade oscillations









• Conclusions

Magnetism in systems with coupled dilute moments and delocalized band electrons

(Ga,Mn)As

cou

plin

g s

tren

gth

/ F

erm

i en

erg

y

band-electron density / local-moment density

HOW DOES ONE GO ABOUT UNDERSTANDING SUCH

SYSTEMS

1. One could solve the full many body S.E.: not possible AND not fun

2. Combining phenomenological models (low degrees of freedom) and approximations while checking against experiments

“This is the art of condensed matter science, an intricate tangobetween theory and experiment whose conclusion can only beguessed at while the dance is in progress”

A.H.M et al., in “Electronic Structure and Magnetism in Complex Materials” (2002).

· Model Anderson Hamiltonian: (s - orbitals: conduction band; p - orbitals: valence band)

+ (Mn d - orbitals: strong on-site Hubbard int. local moment)

+ (s,p - d hybridization)

· Semi-phenomenological Kohn-Luttinger model for heavy, light, and spin-orbit split-off band holes

· Local exchange coupling: Mn: S=5/2; valence-band hole: s=1/2; J

pd > 0

k.p Local Moment - Hamiltonian

IjIjvjI

pd SsRrJ

,

THE SIMPLE MODEL

ELECTRONS

Mn

ELECTRONS-Mn

Large S: treat classically

Two Approximations

2-Mean Field Approximation

MNJh ˆ

extH

rsJH

Field felt by band electrons

Field felt by local moments

1-Virtual Crystal Approximation

N MnIjI

Rr

Bastard, J. de Physique, 39 p. 87 (1978) Gaj, Phys. Stat. Solidi 89 p.655 (1978)

Theoretical Approaches to DMSs

• First Principles LSDA PROS: No initial assumptions, effective Heisenberg model can be extracted, good for determining chemical trends

CONS: Size limitation, difficulty dealing with long range interactions, lack of quantitative predictability, neglects SO coupling (usually)• Microscopic TB models

•k.p Local Moment

PROS: “Unbiased” microscopic approach, correct capture of band structure and hybridization, treats disorder microscopically (combined with CPA), very good agreement with LDA+U calculations

CONS: neglects (usually) coulomb interaction effects, difficult to capture non-tabulated chemical trends, hard to reach large system sizes

PROS: simplicity of description, lots of computational ability, SO coupling can be incorporated, CONS: applicable only for metallic weakly hybridized systems (e.g. optimally doped GaMnAs), over simplicity (e.g. constant Jpd), no good for deep impurity levels (e.g. GaMnN)

Jungwirth, Sinova, Masek, Kucera, MacDonald, Rev. of Mod. Phys. 78, 809 (2006)

Which theory is right?

KP EastwoodFast principles Jack

Impurity bandit vs Valence Joe









• Conclusions

Curie temperature limited to ~110K.

Only metallic for ~3% to 6% Mn

High degree of compensation

Unusual magnetization (temperature dep.)

Significant magnetization deficit

But are these intrinsic properties of GaMnAs ??

“110K could be a fundamental limit on TC”

As

GaMn

Mn Mn

Problems for GaMnAs (late 2002)

Can a dilute moment ferromagnet have a high Curie temperature ?

The questions that we need to answer are:

1. Is there an intrinsic limit in the theory models (from the physics of the phase diagram) ?

2. Is there an extrinsic limit from the ability to create the material and its growth (prevents one to reach the optimal spot in the phase diagram)?

EXAMPLE OF THE PHYSICS TANGO

As

GaMn

Mn Mn

Tc linear in MnGa local moment concentration; falls rapidly with decreasing hole density in more than 50% compensated samples; nearly independent of hole density for compensation < 50%.

Jungwirth, Wang, et al. Phys. Rev. B 72, 165204 (2005)

3/1pxT MnMF

c

Intrinsic properties of (Ga,Mn)As

Ga

As

Mn

Ferromagnetic: x=1-8%

Ga1-xMnxAs

Low Temperature - MBE

courtesy of D. Basov

Inter-stitial

Anti-site

Substitutioanl Mn:acceptor +Local 5/2

moment

As anti-site deffect: Q=+2e

Interstitial Mn: double donor

Extrinsic effects: Interstitial Mn - a magnetism killer

Extrinsic effects: Interstitial Mn - a magnetism killer

Yu et al., PRB ’02:

~10-20% of total Mn concentration is incorporated as interstitials

Increased TC on annealing corresponds to removal of these defects.

Mn

As

Interstitial Mn is detrimental to magnetic order:

compensating double-donor – reduces carrier density

couples antiferromagnetically to substitutional Mn even in

low compensation samples Blinowski PRB ‘03, Mašek, Máca PRB '03

MnGa and MnI partial concentrations

Microscopic defect formation energy calculations:

No signs of saturation in the dependence of MnGa concentrationon total Mn doping

Jungwirth, Wang, et al.Phys. Rev. B 72, 165204 (2005)

As grown Materials calculation

Annealing can vary significantly increases hole densities.

Low Compensatio

n

0 2 4 6 8 100

3

6

9

12

15

18

p (

x 1

020cm

-3)

Mntotal

(%)

0 2 4 6 8 100.0

0.5

1.0

1.5

p/M

n sub

Mntotal

(%)

Obtain Mnsub assuming

change in hole density due to

Mn out diffusion

Open symbols & half closed as grown. Closed symbols annealed

High compensatio

nJungwirth, Wang, et al.Phys. Rev. B 72, 165204 (2005)

Experimental hole densities: measured by ordinary Hall effect

Theoretical linear dependence of Mnsub on total Mn confirmed experimentally

Mnsub

MnIntObtain Mnsub & MnInt assuming change in hole density due to

Mn out diffusion

Jungwirth, Wang, et al.Phys. Rev. B 72, 165204 (2005)

SIMS: measures total Mn concentration. Interstitials only compensation assumed

Experimental partial concentrations of MnGa and MnI in as grown samples

Can we have high Tc in Diluted Magnetic Semicondcutors?

Tc linear in MnGa local (uncompensated) moment concentration; falls rapidly with decreasing hole density in heavily compensated samples.

Define Mneff = Mnsub-MnInt

NO INTRINSIC LIMIT NO EXTRINSIC LIMIT

There is no observable limit to the amount of substitutional Mn we can put in

0 1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

120

140

160

180

TC(K

)

Mntotal

(%)

8% Mn

Open symbols as grown. Closed symbols annealed

0 1 2 3 4 5 6 70

20

40

60

80

100

120

140

160

180

TC(K

)

Mneff

(%)

Tc as grown and annealed samples

● Concentration of uncompensated MnGa moments has to reach ~10%. Only 6.2% in the current record Tc=173K sample

● Charge compensation not so important unless > 40%

● No indication from theory or experiment that the problem is other than technological - better control of growth-T, stoichiometry

- Effective concentration of uncompensated MnGa moments has to increase beyond 6% of the current record Tc=173K sample. A factor of 2 needed 12% Mn would still be a DMS

- Low solubility of group-II Mn in III-V-host GaAs makes growth difficult

Low-temperature MBEStrategy A: stick to (Ga,Mn)As

- alternative growth modes (i.e. with proper

substrate/interface material) allowing for larger

and still uniform incorporation of Mn in zincblende GaAs

More Mn - problem with solubility

Getting to higher Tc: Strategy A

Find DMS system as closely related to (Ga,Mn)As as possible with

• larger hole-Mn spin-spin interaction

• lower tendency to self-compensation by interstitial Mn

• larger Mn solubility

• independent control of local-moment and carrier doping (p- & n-type)

Getting to higher Tc: Strategy B

conc. of wide gap component0 1

latti

ce c

onst

ant (

A)

5.4

5.7

(Al,Ga)As

Ga(As,P)

(Al,Ga)As & Ga(As,P) hosts

d5 d5

local moment - hole spin-spin coupling Jpd S . s

Mn d - As(P) p overlap Mn d level - valence band splitting

GaAs & (Al,Ga)As

(Al,Ga)As & Ga(As,P)GaAs

Ga(As,P)

MnAs

Ga

Smaller lattice const. more importantfor enhancing p-d coupling than larger gap

Mixing P in GaAs more favorable

for increasing mean-field Tc than Al

Factor of ~1.5 Tc enhancement

p-d coupling and Tc in mixed

(Al,Ga)As and Ga(As,P)

Mašek, et al. PRB (2006)Microscopic TBA/CPA or

LDA+U/CPA

(Al,Ga)As

Ga(As,P)

Ga(As,P)

10% Mn

10% Mn

5% Mn

theory

theory

Using DEEP mathematics to find a new material

3=1+2

Steps so far in strategy B:

• larger hole-Mn spin-spin interaction : DONE BUT DANGER IN PHASE DIAGRAM

• lower tendency to self-compensation by interstitial Mn: DONE

• larger Mn solubility ?

• independent control of local-moment and carrier doping (p- & n-type)?

III = I + II Ga = Li + Zn

GaAs and LiZnAs are twin SC

Wei, Zunger '86;Bacewicz, Ciszek '88;Kuriyama, et al. '87,'94;Wood, Strohmayer '05

Masek, et al. PRB (2006)

LDA+U says that Mn-doped are also twin DMSs

No solubility limit for group-II Mn

substituting for group-II Zn !!!!

Electron mediated Mn-Mn coupling n-type Li(Zn,Mn)As -

similar to hole mediated coupling in p-type (Ga,Mn)As

L

As p-orb.

Ga s-orb.As p-orb.

EF

Comparable Tc's at comparable Mn and carrier doping and

Li(Mn,Zn)As lifts all the limitations of Mn solubility, correlated local-moment and carrier densities, and p-type only in (Ga,Mn)As

Li(Mn,Zn)As just one candidate of the whole I(Mn,II)V family




• Impurity band and valence band in doped semiconductors• Low doped insulating GaAs:Mn





• Conclusions

Example: Si:P --- shallow impurity where most of the binding energy is hydrogenic-like.

MI transition occurs when impurity bound states begin to overlap

For GaAs shallow impurities (C,Be,Zn,..) this occurs at 1018 cm-3

For intermediate impurities (Ea~110 meV) this occurs at higherimpurity concentration NMn~1020 cm-3

In Ga1-xMnxAs x=1% corresponds to a substitutional doping concentration of NMn~2.2 x 1020 cm-3

General picture of MI transition in doped semiconductors

General picture of MI transition in doped semiconductors: cross over from IB to VB

Mn-d-like localmoments

As-p-like holes

Mn

Ga

AsMn

EF

DO

S

Energy

spin

spin

with 5 d-electron local moment

on the Mn impurity

valence band As-p-like holes

As-p-like holes localized on Mn acceptors

<< 1% Mn

onset of ferromagnetism near MIT

Jungwirth et al. RMP ‘06

~1% Mn >2% Mn

MI transition in GaMnAs: cross over from IB to VB (no sharp boundary)









• Conclusions

Low doped insulating GaAs:MnActivation energy from dc-transport

J. S. Blakemore, W. J. Brown, M. L. Stass, and D. A. Woodbury, J. Appl. Phys. 44, 3352 (1973).


Sample Mn(4D) has Mn density 1.6 x1017 cm−3(, M5: 1.1 x1018cm−3, M10:1.9 x1019 cm−3, Mn5A: 9.3 x1019 cm−3.

J. S. Blakemore, W. J. Brown, M. L. Stass, and D. A. Woodbury, J. Appl. Phys. 44, 3352 (1973).

M. Poggio, R. C. Myers, N. P. Stern, A. C. Gossard, and D. D. Awschalom, Phys. Rev. B 72,

235313 (2005). MBE grown samples.


Infrared photoabsorption crossection measurements in bulk GaAs:Mn. Mn(4): 1.7 x1017 cm−3, Mn(5): 9.3 x1018 cm−3.

W. J. Brown and J. S. Blakemore, J. Appl. Phys. 43, 2242 (1972).

Expected absorption cross section for a non-shallow impurity (peak at 2Ea)

Consistent with the Ea obtained from the dc-transport, a peak at ~ 200 meV is observed in the weakly doped Mn(4) GaAs:Mn samples. At higher doped sample Mn(5) the peak is slightly red shifted (~ 180 meV) and broadened









• Conclusions

Impurity band to disordered-valence-band cross over in high-doped GaAs:Mn: dc-transport

Jungwirth, Sinova, MacDonald, Gallagher, Novak, Edmonds, Rushforth, Campion, Foxon, Eaves, Olejnik, Masek, Yang, Wunderlich, Gould, Molenkamp, Dietl, Ohno, arXiv:0707.0665

•For Mn doping around 1%, the conductivity curves can no longer be separated into an impurity-band dominated contribution at low temperatures and an activated valence-band dominated contribution at higher temperatures•Above 2%, no activation energy is observed even as high as 500 K where activation across the gap takes over

Impurity band to disordered-valence-band cross over in high-doped GaAs:Mn: dc-transport

Jungwirth, Sinova, MacDonald, Gallagher, Novak, Edmonds, Rushforth, Campion, Foxon, Eaves, Olejnik, Masek, Yang, Wunderlich, Gould, Molenkamp, Dietl, Ohno, arXiv:0707.0665

same growth conditions but <1% insulating

Comparable mobilities of shallow and intermediate acceptor systems

K. S. Burch, et al, Phys. Rev. Lett. 97, 087208 (2006), E. J. Singley, et al, Phys. Rev. Lett. 89, 097203 (2002). E. J. Singley, et al, Phys. Rev. B 68, 165204 (2003).

T=292 K T=7 K

Associating peak to an IB is implausible because of:

(i) the absence of the activated dc-transport counterpart in the high-doped metallic samples,

(ii) the blue-shift of this mid-infrared feature with respect to the impurity band transition peak in the NMn 1019 cm −3 sample,

(iii) the appearance of the peak at frequency above 2Ea,(iv) the absence of a marked broadening of the peak with

increased doping.

Impurity band to disordered-valence-band cross over in high-doped GaAs:Mn: ac-absorption experiments


W. Songprakob, R. Zallen, D. V. Tsu, and W. K. Liu, J. Appl. Phys. 91, 171 (2002).

J. Sinova, et al. Phys. Rev. B 66, 041202 (2002).

GaAs

x=5%

C-doped (shallow acceptor) experimentsat a doping well within the metal side

Virtual crystal approximation (no localizationeffects).

hole density: p=0.2, 0.3, ....., 0.8 nm-3

Hirakawa, et al Phys. Rev. B 65, 193312 (2002)

Impurity band to disordered-valence-band cross over in high-doped GaAs:Mn: red-shift of the IR peak in GaMnAs

At low doping near the MI transitionNon-momentum conserved transitions to localized states at the valence edge take away spectral weight from the low frequency

As metallicity/doping increases the localized states near the band edge narrow and the peak red-shifts as the inter-band part adds weight to the low-frequency part

FINITE SIZE EXACT DIAGONALIZATION STUDIESFINITE SIZE EXACT DIAGONALIZATION STUDIES

S.-R. E. Yang, J. Sinova, T. Jungwirth, Y.P. Shim, and A.H. MacDonald, PRB 67, 045205 (03)

No-localization approximation

Exact diagonalization results in reasonable agreement with as-grown samples

x=4.0%, compensation from anti-sites

x=4.5%,

Lower compensation

x 2

FINITE SIZE EXACT DIAGONALIZATION STUDIESFINITE SIZE EXACT DIAGONALIZATION STUDIES

S.-R. E. Yang, J. Sinova, T. Jungwirth, Y.P. Shim, and A.H. MacDonald, PRB 67, 045205 (03)

6-band K-L model

p=0.33 nm-3, x=4.5%, compensation from anti-sites

p=0.2 nm-3, x=4.0%, compensation from anti-sites

6-band K-L model

GaAs

GaAs









• Conclusions

Effective Moment density, Mneff = Mnsub-MnInt due to AF Mnsub-MnInt pairs.

Tc increases with Mneff when compensation is less than ~40%.

No saturation of Tc at high Mn concentrations

Closed symbols are annealed samples

0 1 2 3 4 5 6 70

20

40

60

80

100

120

140

160

180

TC(K

)

Mneff

(%)

High compensatio

n

Linear increase of Tc with effective Mn

MAGNETIC ANISOTROPY

M. Abolfath, T. Jungwirth, J. Brum, A.H. MacDonald, Phys. Rev. B 63, 035305 (2001)

Condensation energy dependson magnetization orientation

<111>

<110>

<100>

compressive strain tensile strain

experiment:

Lopez-Sanchez and Bery 2003Hwang and Das Sarma 2005

Resistivity temperature dependence of metallic GaMnAs

theory theory

experiment

Ferromagnetic resonance: Gilbert damping

Aa,k()

I

M

Anisotropic Magnetoresistance

exp.

T. Jungwirth, M. Abolfath, J. Sinova, J. Kucera, A.H. MacDonald, Appl. Phys. Lett. 2002

ANOMALOUS HALL EFFECT

T. Jungwirth, Q. Niu, A.H. MacDonald, Phys. Rev. Lett. 88, 207208 (2002)

anomalous velocity:

M0M=0

JpdNpd<S> (meV)

Berry curvature:

AHE without disorder

ANOMALOUS HALL EFFECT IN GaMnAs

Experiments

Clean limit theory

Minimal disorder theory

ConclusionNo intrinsic or extrinsic limit to Tc so far: it is a materials growth issue

In the metallic optimally doped regime GaMnAs is well described by a disordered-valence band picture: both dc-data and ac-data are consistent with this scenario.

The effective Hamiltonian (MF) and weak scattering theory (no free parameters) describe (III,Mn)V metallic DMSs very well in the optimally annealed regime:• Ferromagnetic transition temperatures

Magneto-crystalline anisotropy and coercively Domain structure Anisotropic magneto-resistance Anomalous Hall effect MO in the visible range Non-Drude peak in longitudinal ac-conductivity • Ferromagnetic resonance • Domain wall resistance • TAMR

BUT it is only a peace of the theoretical mosaic with many remaining challenges!!

TB+CPA and LDA+U/SIC-LSDA calculations describe well chemical trends, impurity formation energies, lattice constant variations upon doping

BEFORE 2000

CONCLUSION: directors cut

BUT it takes MANY to do the physics tango!!

Texas A&M U., U. Texas, Nottingham, U. Wuerzburg,

Cambirdge Hitachi, ….

It IS true that it takes two to tango

2000-2004

2006NEW DMSs ,More heterostructures

NEXT

Mn-d-like localmoments

As-p-like holes

Mn

Ga

AsMn

EF

DO

S

Energy

spin

spin

GaAs:Mn – extrinsic p-type semiconductor

with 5 d-electron local moment

on the Mn impurity

valence band As-p-like holes

As-p-like holes localized on Mn acceptors

<< 1% Mn

onset of ferromagnetism near MIT

Jungwirth et al. RMP ‘06

~1% Mn >2% Mn

STILL LARGELY UNEXPLORED SYSTEMATICALLY: MIT

Impurity band to disordered-valence-band cross over in high-doped GaAs:Mn: red-shift of the IR peak in GaMnAs

At low doping near the MI transitionNon-momentum conserved transitions to localized states at the valence edge take away spectral weight from the low frequency

As metallicity/doping increases the localized states near the band edge narrow and the peak red-shifts as the inter-band part adds weight to the low-frequency part

Integrated read-out, storage, and transistor

Low current driven magnetization reversal

Parkin, US Patent (2004)

Magnetic race track memory

Yamanouchi et al., Nature (2004)

2 orders of magnitude lower criticalcurrents in dilute moment (Ga,Mn)As than in conventional metal FMsSinova, Jungwirth et al., PRB (2004)

Wunderlich, et al., PRL (2006)

Ideal to study spintronics fundamentals

Family of extraordinary MR effects, R(M),in ohmic, tunneling, Coulomb-blockade regimes

Low Ms (1-10% Mn moment doping): 100-10 x weaker mag. dipolar interactions can allow for100-10 x denser integration without unintentional dipolar cross-links

Strong SO-coupling:magnetocrystalline anisotropy ~ 10 mT & doping and strain dependent can replacedemagnetizing shape anisotropy fields & local control of magnetic configurations

... and more yet to be fully exploited


Hot electron photoluminescence studies: comparison of Zn doped and Mn doped

Left panel: HPL spectra of GaAs doped with ~ 1017 cm−3 of Zn and ~ 1019 cm−3 of Zn. (replotted in logarithmic scale).

HPL spectra of GaAs doped with ~ 1017 cm−3 of Mn, and of ≈ 1% and ≈ 4% GaAs:Mn materials.

Eex is the HPL excitation energy. Arrows indicate the spectral feature corresponding to impurity band transitions in the low-doped materials.

A. Twardowski and C. Hermann, Phys. Rev. B 32, 8253 (1985).

V. F. Sapega, M. Moreno, M. Ramsteiner, L. D¨aweritz, and K. H. Ploog, Phys. Rev. Lett. 94, 137401 (2005).

Allan MacDonald U of Texas

Tomas JungwirthInst. of Phys. ASCR

U. of Nottingham

Joerg WunderlichCambridge-Hitachi

Bryan GallagherU. Of Nottingham

Tomesz DietlInstitute of Physics, Polish Academy of

Sciences

Other collaborators: Jan Masek, Karel Vyborny, Bernd Kästner, Carten Timm, Charles Gould, Tom Fox,

Richard Campion, Laurence Eaves, Eric Yang, Andy Rushforth, Viet Novak

Hideo OhnoTohoku Univ.

Laurens MolenkampWuerzburg

Jairo SinovaTexas A&M Univ.

Ewelina HankiewiczFordham Univesrsity

Documents

Jairo Sinova (TAMU) Making semiconductors magnetic: A new approach to engineering quantum materials NERC SWAN