Magnetic semiconductors - Fujimori...
Transcript of Magnetic semiconductors - Fujimori...
![Page 1: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/1.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Electronic structure of diluted magnetic semiconductors
• Ferromagnetic semiconductors– Global electronic structure– Electronic structure near the chemical potential -
charge carriers• Soft x-ray magnetic circular dichroism studies
– Identification of ferromagnetic component– Local magnetic susceptibility
![Page 2: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/2.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Electronic structure of diluted magnetic semiconductors
![Page 3: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/3.jpg)
Diluted magnetic semiconductors ADiluted magnetic semiconductors A11--xxMnMnxxX X based on IIbased on II--VI compoundsVI compounds
random Mn substitution
Cd2+1-xMn2+
xTe: Giant Faraday rot.Optical isolators
Zn2+1-xMn2+
xS:Electro-luminescence
InsulatingAF/spin glass
Cd2+Te
Zn2+S
![Page 4: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/4.jpg)
Resonant photoemission spectroscopyResonant photoemission spectroscopyto extract to extract MnMn 33dd partial DOSpartial DOS
Mn
Mn
Mn
Mn
![Page 5: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/5.jpg)
Resonant photoemission from CdResonant photoemission from Cd11--xxMnMnxxTeTe
CI Cluster-model calc.
Band theory
PES BIS
Cd0.35Mn0.65Te Mn 3d PDOS
Unoccupied Mn 3d
satellite
satellite
on-resonance
off-resonance
e↑
t2↑
e↓t2 ↓
PES: L. Ley et al., PRB ’87, BIS: A. Franciosi et al, PRB ’89Band-structure calc: S. H. Wei and A. Zunger, PRB ‘87 Cluster-model calc: T. Mizokawa and A. Fujimori, PRB ‘96Anerson-model calc: O. Gunnarsson et al., PRB ‘88
![Page 6: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/6.jpg)
Electronic structure of CdElectronic structure of Cd11--xxMnMnxxTeTe
e↑
e↓
t2↑
t2 ↓
µ
M. Taniguchi et al., PRB ’86
![Page 7: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/7.jpg)
ConfigurationConfiguration--interaction (CI) cluster model interaction (CI) cluster model for for MnMn impurity in semiconductorimpurity in semiconductor
p hole
d electronNβ
Transfer
integrals: T pd
Charge
-tran
energ
y:
∆
Coulombrepulsion energy: U
Mn
sfer
U, ∆, Tpd : adjustable parameters
-p-d exchange coupling Nβ ~ - Tpd2/(U - ∆ )
![Page 8: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/8.jpg)
Giant magnetoGiant magneto--optical effect through optical effect through pp--dd exchange mechanismexchange mechanism
Mn 3d band(LHB)
Mn 3d band(UHB)
p valence band
conduction bandCd1-xMnxTe∆= 2 eVU = 4 eV
-
p-d exchange couplingNβ ~ - Tpd
2/(U - ∆ )
∆
U-∆
U
p-dexchangeNβ ~ - 1 eV
![Page 9: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/9.jpg)
pp--dd exchange constant exchange constant NNββ for TM impurities in for TM impurities in IIII--VI semiconductors VI semiconductors
-
T. Mizokawa and A.Fujimori, PRB ‘97
![Page 10: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/10.jpg)
Donor and acceptor levels for TM impurities Donor and acceptor levels for TM impurities in IIin II--VI semiconductors VI semiconductors
T. Mizokawa and A.Fujimori, PRB ‘93
![Page 11: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/11.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Ferromagnetic semiconductors
![Page 12: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/12.jpg)
Ferromagnetism in MBEFerromagnetism in MBE--grown grown MnMn--dpoeddpoedIIIIII--V semiconductorsV semiconductors
Growth “phase diagram” of Ga1-xMnxAs Curie temperature of Ga1-xMnxAs
H. Ohno et al., JMMM, ‘99T. Hayashi, M. Tanaka, J. Cryst. Growth, ‘97
![Page 13: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/13.jpg)
Ferromagnetic semiconductors for Ferromagnetic semiconductors for spintronics applications spintronics applications
• Non-volatile memories• GMR devices• New devices utilizing spin injection
Si, Ge GaAs, InAs, ...Y. Ohno et al., Nature ‘99
![Page 14: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/14.jpg)
Transport and magnetoTransport and magneto--transport properties transport properties of Gaof Ga11--xxMnMnxxAs As
Magneto-resistance
~ magnetization
Tc
Resistivity
F. Matsukura et al. PRB ‘98A. Oiwa et al., Solid State Commun. ’97
![Page 15: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/15.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Ferromagnetic semiconductors– Global electronic structure
![Page 16: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/16.jpg)
Resonant photoemission from GaResonant photoemission from Ga11--xxMnMnxxAsAs
On resonance
Off resonance
Mn 3d DOS
J. Okabayashi et al. PRB ‘99
satellite
Semi-insulating GaAs(001)
GaMnAs
As cap
Photon Factory surface interface beamline BL-18A
![Page 17: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/17.jpg)
Comparison with bandComparison with band--structure calculation structure calculation and clusterand cluster--model calculationmodel calculation
p-d exchange Nβ = -1 eV
Mn3+ (substituting Ga3+)Mn2+ + hole
satellite
CI cluster-model calc.assuming Mn2+
Mn is divalent: Mn2+
∆ = 1.5 eVU = 3.5 eV
L. Ley et al., PRB ‘87
Band theory
satellitesatellite
![Page 18: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/18.jpg)
CarrierCarrier--induced ferromagnetism throughinduced ferromagnetism throughpp--dd exchange mechanismexchange mechanism
hole
Ga3+ → Mn3+ → Mn2+ + holesubstitution
p valence band
conduction band Nβ ∼ -1 eV
p hole
Mn 3d band(LHB)
Mn 3d band(UHB)
∆
U-∆ p-d exchange couplingNβ ~ - Tpd
2/(U - ∆ ) ~ -1 eV
large ∆ large Nβdeep p valence band Wide-gap semiconductor
U
![Page 19: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/19.jpg)
Curie temperatures for Curie temperatures for MnMn--doped doped pp--type semiconductors type semiconductors
if hole-doped
Wide-gap semiconductors are predicted to have high TC’sT. Dietl et al, Science (2000)
![Page 20: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/20.jpg)
MnMn 33dd DOS in various DOS in various DMSDMS’’ss and and their CI clustertheir CI cluster--model analysesmodel analyses
satellite
![Page 21: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/21.jpg)
pp--dd exchange coupling from CI clusterexchange coupling from CI cluster--model analysesmodel analyses
∆ U (pdσ) Nβ Ref. .
In1-xMnxAs 1.0 3.5 -0.8 -0.7 1Ga1-xMnxAs 1.5 3.5 -1.0 -1.0 2
Ga1-xMnxN 4.0 5.0 -1.5 -1.6 3
Cd1-xMnxTe 2.0 4.0 -1.1 4
Zn1-xMnxO 6.5 5.2 -1.6 -2.7 5Zn1-xMnxS 3.0 4.0 -1.3 -1.3 4Zn1-xMnxSe 2.0 4.0 -1.1 -1.0 4Zn1-xMnxTe 1.5 4.0 -1.0 -0.9 4
Ref.1 J. Okabayashi et al., PRB ‘02Ref.2 J. Okabayashi et al., PRB ‘99Ref.3 J.-I. Hwang et al., PRB, in pressRef.4 T. Mizokawa et. al., PRB ‘93Ref.5 T. Mizokawa et. al., PRB ‘02
Wide-gap semiconductors indeed have large Nβ.However, it is difficult to dope them with holes.
![Page 22: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/22.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Ferromagnetic semiconductors– Electronic structure near the chemical potential –
charge carriers
![Page 23: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/23.jpg)
Band structure of GaAs and GaBand structure of GaAs and Ga11--xxMnMnxxAsAs
8
6
4
2
0
GaAs
∆ ΓX
Bin
ding
Ene
rgy
(eV
)
8
6
4
2
0
Ga0.965Mn0.035As
∆ ΓX
Bin
ding
Ene
rgy
(eV
)J. Okabayashi et al. PRB 2001
GaAs Ga0.965Mn0.035As
![Page 24: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/24.jpg)
““ImpurityImpurity”” band near Eband near EFF in Gain Ga11--xxMnMnxxAsAs
Ga0.931Mn0.069As - GaAs difference
GaMnAsGaAs
“impurity” band
“impurity” band
J. Okabayashi et al. PRB 2001
![Page 25: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/25.jpg)
Fermi edge in Fermi edge in GaGa11--xxMnMnxxAs ?As ?
J. Okabayashi et al.
-2.0 -1.5 -1.0 -0.5 0 0.5eVEnergy Relative to EF (eV)
Ga0.95Mn0.05As
11K 300 K GaAs (300 K)
Au
hν=50 eV
Inte
nsity
(arb
. uni
ts)
MBE-in situ PES exptPhoton Factory BL-1CWeak Fermi edge at low temperatures
Disappears at high temperatures
-1.0 -0.8 -0.6 -0.4 -0.2 0eV
11K 300 K GaAs
Ga0.95Mn0.05As; hν=80 eV
Energy Relative to E F (eV)In
tens
ity (a
rb. u
nits
)
Au
“impurity” band
![Page 26: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/26.jpg)
““ImpurityImpurity”” band near Eband near EFF in Gain Ga11--xxMnMnxxAsAs
wide energy distribution
low DOS at EF
acceptor level
Undoped semiconductor
Doped semiconductor
Heavily doped, degenerate semiconductor
Mn-doped semiconductor
![Page 27: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/27.jpg)
HightHight DOS at EDOS at EFF according to bandaccording to band--structure structure calculationscalculations
0-4-8 4
J.H. Park et al., Physica B ’00. K. Sato et al., Europhys. Lett. ‘03
![Page 28: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/28.jpg)
NonNon--Drude behavior of optical conductivity Drude behavior of optical conductivity in Gain Ga11--xxMnMnxxAsAs
K. Hirakawa et al., PRB ’02.no Drude peakno Drude peak
Phonon peaks
Y. Nagai et al., JJAP ’01.
![Page 29: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/29.jpg)
Magnetic Magnetic polaronspolarons in in GaGa11--xxMnMnxxAs ?As ?
Weak or no Fermi edge in photoemission spectraNo Drude weight in optical spectra
A. Kaminski and S. Das Sarma, PRL ‘02
--- (Magnetic) polaron ?Incoherent metal
![Page 30: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/30.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Soft x-ray magnetic circular dichroism studies– Identification of ferromagnetic component
![Page 31: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/31.jpg)
Soft xSoft x--ray magnetic circular dichroism (XMCD)ray magnetic circular dichroism (XMCD)in corein core--level xlevel x--ray absorption (XAS) spectraray absorption (XAS) spectra
spin sum rule
orbital sum rule
Mn 2pcore level
Mn 3dvalence level
hν
+sensitive to local chemical environment
microscopic, element specific probe
![Page 32: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/32.jpg)
Sensitivity of XAS and XMCD to chemical Sensitivity of XAS and XMCD to chemical environmentenvironment
Atomic Co in K Co metal
Atomic multiplet structure characteristic of * valence, * spin, * crystal field
P. Gambardella et al., PRL ‘02 C.T. Chen et al., PRL ‘95
![Page 33: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/33.jpg)
MCD装置
ARPES装置
XMCD endstation at JAERI beamline BLXMCD endstation at JAERI beamline BL--23SU 23SU of Springof Spring--88
Helical undulator with phase modulation
Superconducting magnet, up to 10 TLow temperature, down to 10 KHigh energy resolution and brightness
10m VLS PGMY. Saitoh et al., Nucl. Instrum. Meth. A ‘01
![Page 34: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/34.jpg)
RoomRoom--temperature ferromagnetism in Titemperature ferromagnetism in Ti11--xxCoCoxxOO22
TEM SEMAnatase
Rutile
XRD, UV-VIS MCD --> no precipitation
![Page 35: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/35.jpg)
(a) Co L2,3-edge XAS
Photon Energy (eV)
780 790 800
Intensity (Arb. U
nits)
0
1
2
3
4
5
6
L3 L2
As-grown
2-min.
10-min.
20-min.
Co-metal
(b) Co L2,3-edge XMCD
Photon Energy (eV)
780 790 800 8100
2
4
6
8
As-grown
2-min.
10-min.
20-min.
Co-metal
ρ+
ρ−
(c) ρ+ − ρ−
Photon Energy (eV)
780 790 800 810-1
0
1
2
3
4As-grown
2-min.
10-min.
20-min.
Co-metal
Y.J. Kim et al. PRL ‘03
Ferromagnetism is due to Co metal segregation.
Co 2Co 2pp corecore--level XAS and XMCD of Tilevel XAS and XMCD of Ti11--xxCoCoxxOO22: : Effect of annealingEffect of annealing
~400oC ~400oC
Anatase
![Page 36: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/36.jpg)
RoomRoom--temperature ferromagnetism temperature ferromagnetism in Znin Zn11--xxCoCoxxOO
carrier concentration
Magnetization
H. Saeki et al., J. Phys. Cond. Mat. ‘04
O CZn o
M. Venkatesan et al., PRL ‘04
![Page 37: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/37.jpg)
Co 2Co 2pp corecore--level XAS and XMCD of Znlevel XAS and XMCD of Zn11--xxCoCoxxO:O:Comparison with Co metalComparison with Co metal
M. Kobayashi et al., cond-mat/05, to PRB
Co metal MCD : C. T. Chen et al, PRL ‘95
2.0
1.5
1.0
0.5
0
Abso
rptio
n (a
rb. u
nits)
µ+
µ−
Back Ground
Zn1-xCoxO (x=0.05) Co L2,3 edge
Magnetic Field : 4.5 TTemperature : 20 K
2.0
1.5
1.0
0.5
0
XAS
(arb
. uni
ts)
(µ+ + µ−)/2
-0.10
-0.08
-0.06
-0.04
-0.02
0
0.02
XMCD
(arb
. uni
ts)
800795790785780775770
Photon Energy (eV)
µ+ − µ
−
-0.10
-0.08
-0.06
-0.04
-0.02
0
0.02
XM
CD (a
rb. u
nits)
800795790785780775770
Photon Energy (eV)
Zn0.95Co0.05O Co metal
Co L2,3 edge
-0.08
-0.04
0
782780778776
Co L3
Co metal
Zn1-xCoxOXAS
MCD
Comparison with Co metal
![Page 38: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/38.jpg)
Co 2Co 2pp corecore--level XAS and XMCD of Znlevel XAS and XMCD of Zn11--xxCoCoxxO:O:Comparison with atomic Comparison with atomic multipletmultiplet calc.calc.
784782780778776Photon Energy (eV)
Co L3
798796794792790Photon Energy (eV)
Co L2
XA
S (a
rb. u
nits
)
800795790785780775770Photon Energy (eV)
Co2+, 10Dq=-0.7 eV
Co2+, 10Dq=+0.5 eV
Co3+, 10Dq=-0.5 eV
Co3+, 10Dq=+0.5 eV
Zn0.95Co0.05O Co L2,3 XAS at H=7.0T, T=20K
XM
CD
(arb
. uni
ts)
800795790785780775770Photon Energy (eV)
Zn0.95Co0.05O Co L2,3 XMCD at H=7.0T, T=20K
Co2+, 10Dq=-0.7 eV
Co2+, 10Dq=+0.5 eV
Co3+, 10Dq=-0.5 eV
Co3+, 10Dq=+0.5 eV
784782780778776Photon Energy (eV)
Co L3
798796794792790Photon Energy (eV)
Co L2
・10Dq > 0Oh symmetry
・10Dq < 0Td symmetry
Ferromagnetismis due to Co2+
substituting Zn
M. Kobayashi et al., cond-mat/05, to PRB
![Page 39: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/39.jpg)
Room temperature ferromagnetism in Room temperature ferromagnetism in ZZnn11--xxCrCrxxTeTe
H. Saito et al., PRL ‘03
![Page 40: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/40.jpg)
Cr 2Cr 2pp corecore--level MCD of Znlevel MCD of Zn11--xxCrCrxxTe (x=0.045)Te (x=0.045)
590580570
XA
S or
XM
CD
(arb
. uni
ts)
Photon energy (eV)
Te M4,5 µ+
µ-
(µ++ µ-)/2
(µ+- µ-)/2
XAS
XMCD×5
Zn1-xCrxTe (x = 0.045)B = 2 TT = 20 K
Cr L3 Cr L2
0.20
0.15
0.10
0.05
0.0086420
Field (T)Cr L
3 XM
CD
inte
nsity
(a.u
.)
T = 20 K
0.20
0.15
0.10
0.05
0.00250200150100500
×5
Temperature (K)Cr L
3 XM
CD
inte
nsity
(a.u
.)
B = 2 T B = ~0.1 T TC ~ 70 K
Y. Ishida et al.
![Page 41: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/41.jpg)
Comparison with atomic multiplet calculationComparison with atomic multiplet calculation
600590580570
10 Dq = 3.0 eV
2.5
2.0
1.5
1.0
0.5
0
Cr2+(d4) Tetrahedral
Hig
h sp
in
Low
spin
600590580570
Cr2+(d4) Octahedral10 Dq = 3.0 eV
2.5
2.0
1.0
1.5
0.5
0
Photon energy (eV)
600590580570
Cr3+(d3) Tetrahedral
10 Dq = 3.0 eV
2.5
2.0
1.5
1.0
0.5
0
Expt
G. van der Laan and I.W. Kirkman, ‘92
t2
e
![Page 42: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/42.jpg)
Magnetic semiconductorsMagnetic semiconductors
• Soft x-ray magnetic circular dichroism studies– Local magnetic susceptibility
![Page 43: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/43.jpg)
Soft xSoft x--ray magnetic circular dichroism (XMCD)ray magnetic circular dichroism (XMCD)in corein core--level xlevel x--ray absorption (XAS) spectraray absorption (XAS) spectra
A1 - A2
spin sum rule
orbital sum rule
Mn 2pcore level
Mn 3dvalence level
hν
microscopic, element specific probe+
magnetism specific probeParamagnetic ? Ferromagnetic ?
![Page 44: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/44.jpg)
Separation of XMCD signals into ferromagnetic Separation of XMCD signals into ferromagnetic and paramagnetic componentsand paramagnetic components
SQUID data of DMS thin film sample
-150
-100
-50
0
50
100
150
Mag
netiz
atio
n x1
0-6 (e
mu)
-20 -10 0 10 20Magnetic Field (kG)
@5K @300K
M = Mdia + Mferro + Mpara
XMCD of ferromagnetic component
XMCD of paramagnetic component
300 K
5 K
or
XMCD signals
No contribution to XMCD signals
![Page 45: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/45.jpg)
Indication of multiple Indication of multiple MnMn species in Gaspecies in Ga11--xxMnMnxxAs As
Magnetization curvesCurie temperature of Ga1-xMnxAs
T = 2 K
x = 0.071
0.053
0.043
0.035
A. Oiwa et al., Solid State Commun. ’97 H. Ohno et al., JMMM, ‘99
![Page 46: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/46.jpg)
Interstitial Interstitial MnMn in Gain Ga11--xxMnMnxxAs ?As ?
Mn substituting Ga sites (MnGa): Mn3+ Mn2+ + holeMn at interstitial sites (MnI): Mn0 Mn2+ + electrons: compensates holes !
Change of TC by post annealing Molecular dynamics simulation of MBE
As Ga
Annealing converts MnI to MnGa ? First, Mn enters interstices then Ga siteS.J. Potashnik et al., APL (2001) S.C. Erwin and A.G. Petukhov PRL ‘02
![Page 47: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/47.jpg)
Two signals in Two signals in MnMn 22pp XAS spectra of GaXAS spectra of Ga11--xxMnMnxxAsAsand LTand LT--annealing effectannealing effect
Interstitial Mn ?Substitutional Mn ?
Y. Ishiwata et al., PRB ‘02
![Page 48: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/48.jpg)
Previous XMCD studies of GaPrevious XMCD studies of Ga11--xxMnMnxxAs As
x = 0.02T = 15 - 30 KH = 0.55 T
Mn 2p Mn 2p
As 2p3/2
Evidence for carrier-induced magnetism
Y. L. Soo et al., PRB ‘03
H. Ohldag et al., APL ‘00 D. J. Keavney et al., PRL ‘03
![Page 49: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/49.jpg)
MnMn 22pp XMCD spectra of GaXMCD spectra of Ga11--xxMnMnxxAs As
Y. Takeda et al.
s.i. GaAs(001)
GaMnAs
As cap
20 nm1 nm
GaAs
Tc = 40 K
10Dq = -0.7 eV
A. Tanaka
Atomic multiplet calc. for Mn2+
![Page 50: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/50.jpg)
MnMn 22pp XMCD spectra of GaXMCD spectra of Ga11--xxMnMnxxAs As
TC ~ 40 K
Y. Takeda et al.
![Page 51: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/51.jpg)
MagneticMagnetic--field and temperature dependencesfield and temperature dependencesof XMCD intensity of XMCD intensity
20 K < Tc
100 K > Tc
4.2%
4.2%
7.8 %
7.8 %Ferromagnetic
component
Paramagnetic component
4.2%: TC ~ 40 K7.8%: TC ~ 60 K
Y. Takeda et al.
![Page 52: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/52.jpg)
MnMn 22pp XMCD spectra of GaXMCD spectra of Ga11--xxMnMnxxAs As
TC ~ 40 K
PF
Y. Takeda et al.
![Page 53: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/53.jpg)
Decomposition of XMCD signals intoDecomposition of XMCD signals intoferromagnetic and ferromagnetic and ““paramagneticparamagnetic”” componentscomponents
F
P
4.2%
4.2%
7.8 %
7.8 %
T = 20 K < Tc
PF
4.2%: TC ~ 40 K7.8%: TC ~ 60 K
Y. Takeda et al.
![Page 54: Magnetic semiconductors - Fujimori Groupwyvern.phys.s.u-tokyo.ac.jp/f/lecture/apctp/APCTP_5_DMS.pdf · Magnetic semiconductors • Electronic structure of diluted magnetic semiconductors](https://reader030.fdocuments.net/reader030/viewer/2022033121/5e1f3b30a3a101162c63e522/html5/thumbnails/54.jpg)
Two signals in Two signals in MnMn 22pp XAS spectra of GaXAS spectra of Ga11--xxMnMnxxAsAsand LTand LT--annealing effectannealing effect
Interstitial Mn ?Substitutional Mn ?
Substitutional MnOut-diffused Mn from interstitial sites
Fist-principles calc.In situ Auger, resistivity meas.K. W. Edmonds et al, PRL ‘04
Y. Ishiwata et al., PRB ‘02