Magnetic semiconductors Classical magnetic semiconductors Diluted magnetic semiconductors Ferromagnetic semiconductors New materials, nanostructures, interfaces
Magnetic semiconductors Classical magnetic semiconductors
History of magnetic semiconductors 1st generation 1960 s- Gd 2 S 3, EuO, CdCr 2 Se 4,. ferromagnetic, semiconducting 2nd generation 1980 s Cd 1-x Mn x Te, (Mn in II-VI) antiferromagnetic, insulating applied for magneto-optical devices 3rd generation 1990 s- Ga 1-x Mn x As, (Mn in III-V), oxide DMS ferromagnetic, metallic spin-controlled semiconductor devices
MCD of spinel-type CdCr 2 X 4 and CuCr 2 X 4 metallic Cr 3.5+ metallic Cr 3.5+ sum rule <L Z > = 0 semicond Cr 3+ No change in XAS, MCD holes enter p orbitals A. Kimura et al., PRB 01
Magnetic circular dichroism (MCD) in core-level absorption
Magnetic semiconductors Diluted magnetic semiconductors
Diluted magnetic semiconductors A 1-x Mn x B II-VI, III-V semiconductor host + substitutional Mn ions Mn
Resonant photoemission from Cd 1-x Mn x Te Photoemission BIS On resonance. Band theory Off resonance. Difference = Mn 3d DOS Cluster calc. satellite main = 2 ev U = 4 ev Exp: Ley, Taniguchi, Fujimori,... PRB 87 Calc: Mizokawa, Fujimori, PRB 96 cf. Gunnarsson and Jepsen, PRB 88 near E F dominated by p character Nβ ~ -1 ev ( - ) Strong mageneto-optical effects
Resonant photoemission discrete level continuous level
Cluster model for transition-metal impurity in semiconductor d electron Nβ p hole U,, Tpd : adjustable parameters p-d exchange constant Nβ ~ - T pd2 /(U- )
Configuration-interaction cluster-model analysis of d-electron photoemission spectra Ground state Final states Photoemission satellite Ground state main Intensities
Configuration-interaction cluster(anderson)- model picture of TM impurity in semiconductor N N-1 N+1 T. Mizokawa and A.F., PRB 93
Intra-atomic d-d transitions for TM impurity in ZnS T. Mizokawa and A.F., PRB 93
Configuration-interaction cluster(anderson)- model picture of TM impurity in semiconductor N N-1 N+1 T. Mizokawa and A.F., PRB 93
Effects of ligand atom for Mn impurity in II-VI semiconductors d-d optical transitions CI calc. Expt. T. Mizokawa and A.F., PRB 93
Configuration-interaction cluster(anderson)- model picture of TM impurity in semiconductor N N-1 N+1 T. Mizokawa and A.F., PRB 93
Donor and acceptor levels for Mn impurity in II-VI semiconductor T. Mizokawa and A.F., PRB 93
Donor and acceptor levels for TM impurity in II-VI semiconductors T. Mizokawa and A.F., PRB 93
p-d exchange constant Nβ for TM impurity in II-VI semiconductors - T. Mizokawa and A.F., PRB 97
Magnetic semiconductors Ferromagnetic semiconductors
Ferromagnetism in MBE-grown Ga 1-x Mn x As Growth phase diagram Curie temperature T. Hayashi, M. Tanaka, J. Cryst. Growth, 97 H. Ohno et al., JMMM, 99
Transport and magneto-transport properties of Ga 1-x Mn x As Mn concentration dependence of electrical resistivity Magneto-resistance T C ~ magnetization F. Matsukura et al. PRB 98
Photon Factory surface interface beamline BL-18A CDM + ADES 400, CLAM 3
Comparison with band-structure calculation and cluster-model calculation Mn 3+ Mn 2+ + hole hole main satellite main = 1.5 ev U = 3.5 ev satellite p-d exchange Nβ = -1 ev
Mechanism for carrier-induced ferromagnetism Double exchange no (holes have p character) RKKY interaction no (Fermi energy << Nβ ) p-d exchange most likely p hole Nβ -1 ev
ARPES form 3D material
Band structures of GaAs and Ga 1-x Mn x As GaAs GaAs Ga 0.965 Mn Mn 0.035 As 0.035 As 0 0 Binding Energy (ev) 2 4 6 Binding Energy (ev) 2 4 6 8 8 X Γ X Γ Okabayashi et al. PRB 2001
Impurity band near E F in Ga 1-x Mn x As Ga 0.931 Mn 0.069 As - GaAs difference GaMnAs GaAs impurity band Okabayashi et al. PRB 2001
Difference between Ga 1-x Mn x As and In 1-x Mn x As InMnAs: Tc max ~ 50 K GaMnAs: Tc max ~ 100 K Drude peak Optical absorption Lattice constants InMnAs no Drude peak GaMnAs H. Ohno et al., APL 96 K. Hirakawa et al., Physica E, 2001 K. Hirakawa et al., PRB, submitted
Resonant photoemission from Ga 1-x Mn x As and In 1-x Mn x As On resonance Off resonance Mn 3d DOS J. Okabayashi et al. PRB 02
Cluster model analyses for Ga 1-x Mn x As and In 1-x Mn x As InMnAs: =1.0 ev, (pdσ)=0.8ev--> Nβ= -0.7 ev GaMnAs: =1.5 ev, (pdσ)=1ev--> Nβ= -1.0 ev
impurity states in Ga 1-x Mn x As and In 1-x Mn x As Ga 0.931 Mn 0.069 As (In,Mn)As Γ Intensity (arb. units) GaMnAs GaAs 18 ev 20 22 24 26 28 Intensity (arb. units) InMnAs InAs 20 22 24 26 28 30 32 30 34 32 35 40 1 0 Binding Energy (ev) -9.0-9.3-9.5-9.8-10.0-10.3-10.5 X 36 40 45 50 1 0.5 0-0.5 Binding Energy (ev)
Difference between Ga 1-x Mn x As and In 1-x Mn x As Ga 1-x Mn x As In 1-x Mn x As strong p-d hybridization weak large Nβ small high Tc low yes split-off states/ impurity band no quasi-bound holes free holes non-drude Drude J. Okabayashi et al. PRB 02
Curie temperatures for Mn-doped p-type semiconductors if hole-doped! T. Dietl et al, Science (2000)
Magnetic semiconductors New materials, nanostructures, interfaces
n-type Zn 1-x Mn x O Magnetic susceptibility Optical absorption T. Fukumura et al. APL 99
T. Mizokawa et al. PRB 02 Mn 3d DOS of Zn 1-x Mn x O and cluster-model analysis Resonant photoemission Cluster model analysis = 6.5 ev U = 5.2 ev Nβ= -2.7eV On resonance O resonance Mn 3d DOS 3 ev 4 ev 2 ev 4 ev 1.5 ev 4 ev 1.5 ev 3.5 ev -1.3eV -1.0eV -1.0eV -0.9eV
Electronic structure of n-type and p-type Zn 1-x Mn x
Ferromagnetism in n-type Zn 1-x V x oxygen deficiency ferromagnetic H. Saeki et al., Solid State Commun. 2001
Photoemission spectra of n-type Zn 1-x V x Zn 3d Zn 1-x V x O n-zno O 2p Paramagnetic V 3d Ferromagnetic Y. Ishida et al., unpublished
Room-temperature ferromagnetism? in Ga Mn x N Ga 1-x Mn S. Sonoda et al., JJAP 01
Nano-scale MnAs dots on S-passivated GaAs hypothetical zinc-blende-type MnAs theoretically predicted ferromagnet (Shirai et al.) K.Ono et al., JAP 02
Photoemission spectra of MnAs dots zinc-blende type most likely zinc-blende type hexagonal NiAs type
Mn 2p x-ray absorption of MnAs dots Expt. at SRRC J. Okabayashi et al., unpublished
Room temperature ferromagnetism in CdGeP 2, ZnGeP 2 - - 2 -based DMS CdGeP 2 :Mn ZnGeP 2 :Mn CdSnP 2 :Mn Mn deposition thermal treatment at 400 Chalcopyrite structure Zn Ge P G.A. Medvedkin et al., JJAP 00
Room temperature ferromagnetism in bulk Zn 1-x Mn x GeP 2x B.J. Kim et al., PRL 02
Valence-band photoemission form ZnGeP 2 : Mn ZnGeP2:Mn hv=70ev d(å)=250 Intensity (arb.units) 125 64 32 16 Strong Mn Auger (like MnX compounds) 8 4 2 0 Zn3d 12 10 8 6 4 2 0 Binding energy (ev) Mn 3d resonance No Mn Auger (like II-VI, II-V DMS) Y. Ishida et al., unpublished
Core-level intensities for ZnGeP 2 : Mn 3.0 Mn deposition series Core level intensity (arb.units) 2.5 2.0 1.5 1.0 0.5 Ge 3d Mn 2p P 2p sputtering series Zn 2p3/2 0.0 10 2 3 4 5 6 7 10 2 3 4 5 6 7 100 2 3 4 5 Nominal Mn thickness (A) Y. Ishida et al., unpublished