1. Summary and prospects in the field of magnetically doped semiconductors
Tomasz Dietl
Laboratory for Cryogenic and Spintronic Research,
Institute of Physics, Polish Academy of Sciences
Institute of Theoretical Physics, University of Warsaw, Poland
WPI-AIMR Tohoku University, Sendai, Japan
FunDMS
see, A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010)
T. Dietl and H. Ohno, Rev. Mod. Phys. 86, 187 (2014)

2. Summary and prospects in the field of magnetically doped semiconductors
Tomasz Dietl
Laboratory for Cryogenic and Spintronic Research,
Institute of Physics, Polish Academy of Sciences
Institute of Theoretical Physics, University of Warsaw, Poland
WPI-AIMR Tohoku University, Sendai, Japan
FunDMS
see, A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010)
T. Dietl and H. Ohno, Rev. Mod. Phys. 86, 187 (2014)
Unanticipated richness of materials science challenges
Test beds for spintronic functionalities

3. Magnetically doped semiconductors
Accomplishments

4. Magnetically doped semiconductors
Accomplishments
Prospects, challenges, emerging fields, …

5. Magnetically doped semiconductors
Accomplishments
Prospects, challenges, emerging fields, …
Role of nuclear methods (other talks, discussion, )
characterization, fabrication, …

6. Moessbauer isotopes

7. Moessbauer isotopes
and more ….
channeling

8. Outline Mamagnetically doped semiconductors summary, prospects,
challenges, emerging fields, …

9. Outline Mamagnetically doped semiconductors summary, prospects,
challenges, emerging fields, …
dopants
semiconductors
magnetic interactions
magnetic ground states
functionalities

10. Outline Mamagnetically doped semiconductors summary, prospects,
challenges, emerging fields, …
dopants
semiconductors
magnetic interactions
magnetic ground states
functionalities
The case study – magnetically-doped nitrides  Alberta Bonanni

12. Dilute magnetic semiconductors (DMSs)
III-V
II-VI
Al P Cr Zn S Cr
Ga As Mn Cd Se Mn
In Sb Fe Hg Te Fe
Galazka ‘77

13. Magnetic elements

14. Magnetic dopants Transition metals: open 3d shell but also 4d e.g. Ru
Rare earth: 4f but also actinides: 5f, e.g. U
Magnetically active defects and impurities
d0 ferromagnetism
p ferromagnetism
Contamination

15. Magnetic dopants Transition metals: open 3d shell but also 4d e.g. Ru
Rare earth: 4f but also actinides: 5f, e.g. U
Magnetically active defects and impurities
d0 ferromagnetism
p ferromagnetism
Contamination
doping methods:
also ion implantation, isotope transmutation, …

16. Single impurity limit

17. TM, RE doping – single impurity limit
Questions
answers depend on growth method/co-doping
incorporation into the lattice – not always cation substitution
energy levels
electrical activity
charge and spin state
Jahn-Teller distortion
hybridization with band states
defect generation
formation of complexes
with defects/impurities ….
T.D. (SST’2002)

18. Interstitial position
e.g. part of Mn in MBE-(Ga,Mn)As)
Mn interstitials:
-- donors  compensate holes
-- form AF pairs with MnGa
 compensate spins
K. M. Yu et al. (Berkeley,
Notre-Dame, PRB’2012)

19. Antisite position e.g. part of Mn in Mn-implanted (Ga,Mn)N
- channeling
L.M.C. Pereira et al.
(Leuven, Lisboa) PRB'12

20. Complexes e.g. Mn-Mgk complexes in (Ga,Mn)N:Mg
T. Devillers et al. (Linz, Warsaw), Sci. Reports 2012

21. Contamination e.g. etched Si 300 K 300 K
P. J. Grace et al. (TCD, Weizmann)
Adv. Mat.’09

22. Contamination e.g. etched Si 300 K 300 K
P. J. Grace et al. (TCD, Weizmann)
Adv. Mat.’09

23. Contamination e.g. etched Si  Fe from glass
300 K
300 K
P. J. Grace et al. (TCD, Weizmann)
Adv. Mat.’09
 Fe from glass
Fe-containing nanoparticles main source of ferro contamination

24. Many impurities - DMS

25. Distribution of magnetic dopants
Key insight
d orbitals contribute to bonding
 attractive force between TM cations (chemical interactions)
 non-random distribution of TM ions at thermal equilibrium
Exceptions (true DMSs)
-- (II,Mn)VI
-- growth far from thermal equilibrium, e.g., LT-MBE of (Ga,Mn)As
Types of non-random distribution
-- crystallographic phase separation (precipitation)
-- chemical phase separation (spinodal decomposition)
 locally high density of TM 
condensed magnetic semiconductors (CMS)

26. Nanocrystals e.g., annealed (Ga,Mn)As Hexagonal MnAs
nanocrystals in GaAs
Cubic (Mn,Ga)As
nanocrystals in GaAs
M. Moreno et al. (Berlin) JAP’02

27. Nanocolumns wz-(Al,Cr)N zb-(Zn,Cr)Te (Ge,Mn) TEM/EDS TEM/EELS 25nm
N. Yotaro, et al. (Tsukuba, Warsaw) MRS Proc.’09
L. Gu et al. (Arizona) JMMM’06
(Ge,Mn)
TEM/EELS
M. Jamet et al. (Grenoble)
Nature Mat. ’06
cf. D. Bougear et al..
(WSI Garching)

28. Controlling TM distribution
TM distribution depends more on growth/processing
than on TM/host combination
Aggregation can be enhanced by
-- high growth temperature
-- slow growth rate
Can be affected by changing valence of TM ions
-- co-doping
-- electrical/optical carrier injection during growth

29. Effect of doping on spinodal decomposition
TM charge state is controlled by co-doping with shallow impurities. Because of Coulomb repulsion spinodal decomposition is blocked if TM is charged
Cr+2 EF
ZnTe
Cr+3
ZnTe:N
T.D., Nature Mat.’06
L.-H. Ye et al. (NWU) PRB’06

30. Effect of co-doping on magnetism
[I] ~ 2 x 1018 cm-3 Cr2+
Te-rich growth Cr2+/Cr3+
[N] ~ 3 x1020 cm-3 Cr3+
S. Kuroda … T.D. (Tsukuba, Warsaw) Nature Mat., ’07

31. Effect of co-doping on Cr distribution
I-doped
50nm
Optimized
TEM/EDS
Inhomogeneous
S. Kuroda ... T.D. (Tsukuba, Warsaw) Nature Mat., ’07

32. Effect of co-doping on Cr distribution
I-doped
N-doped
50nm
Optimized
N-doped
TEM/EDS
Inhomogeneous
Homogeneous
S. Kuroda … T.D. (Tsukuba, Warsaw) Nature Mat., ’07

33. Magnetic interactions between localized spins
Dominant interaction in non-metals -- superexchange
TM cation
TM cation
anion
Always present:
usually antiferromagnetic, e.g. Mn2+ [reduces M(T,H)]
DMS – random antiferromagnets
spin-glass freezing at low T

34. Zn1-xCoxO – inverse magnetic susceptibility
grown by ALD at 160oC
x = 42%
M. Sawicki et al. [Warsaw] PRB’2013
antiferromagnetic superexchange

35. Zn1-xCoxO – spin-glass freezing
M. Sawicki et al. [Warsaw] PRB’2013

36. Effects of TM spins on band states
sp-d exchange interaction in DMSs
H = - Isp-dsS
-- spin disorder scattering
-- formation of magnetic polarons
-- giant spin splitting of bands proportional
to magnetization of localized spins

37. Giant splitting of exciton states ~ M(T,H)
E ~ M ~ BS(H)
c.b.
v.b.
geff > 102
J. Gaj et al., R. Planel,..
A. Twardowski et al.
G. Bastard, …
-- p-d: Ipd  No  eV
large p-d hybridization and large intra-site Hubbard U =>
kinetic p-d exchange
-- s-d: Isd  No  0.2 eV
no s-d hybridization => potential s-d exchange

38. Ferromagnetic superexchange
TM cation
TM cation
anion
usually antiferromagnetic, e.g. Mn2+ [reduces M(T,H)]
sometimes ferromagnetic [enhances M(T,H)]
eg. (Ga,Mn)N with Mn3+, TC up to 12 K
 ferromagnetic Mott-Hubbard insulator
cf. Alberta Bonanni

39. RKKY and Bloembergen-Rowland mechanism
spin polarisation
of carriers
spin polarisation of
valence electrons
 Dominates in topological insulators
4th order process in hybridisation <k|H |d>

40. Zener/RKKY model of ferromagnetism
Competition between entropy, AF interactions, and
lowering of carrier enrgy owing to spin-splitting
Curie temperature TC = TCW = TF – TAF superexchange
TF = S(S+1)xeffNo(s)(EF)I2/12
(s)(EF) ~ m*kFd-2
(if no spin-orbit coupling, parabolic band)
=> TC ~ 50 times greater for the holes
large m*
large Ip-d
T.D. et al. PRB’97,’01,‘02, Science ’00

41. Making DMS ferromagnetic – p-type doping
holes mediate ferro coupling in DMS
source of holes in Mn-based DMSs, x < 10%:
Mn itself III-V
(In,Mn)As; (Ga,Mn)As H. Ohno et al. [IBM, Tohoku] PRL’92, APL’96
(Sb,Mn)2Te3; (Bi,Mn)2Te3 Choi et al. [Ulsan] pps(b)’04
TC up to 190 K
TC up to 20 K

42. Making DMS ferromagnetic – p-type doping
valence band holes mediate ferro
coupling in p-type DMS
source of holes in Mn-based DMSs, x < 10%:
Mn itself III-V
(In,Mn)As; (Ga,Mn)As H. Ohno et al. [IBM, Tohoku] PRL’92, APL’96
(Sb,Mn)2Te3; (Bi,Mn)2Te3 Choi et al. [Ulsan] pps(b)’04
acceptor impurities
(Cd,Mn)Te:N, (Zn,Mn)Te:P
TD, Cibert et al. [Grenoble, Warsaw] PRB’97, PRL’97, PRL’03
(K,Ba)(Zn,Mn)2As2 et al. [Beijing, Columbia U.] Nat. Commun.’13
TC up to 190 K
TC up to 20 K
TC up to 5 K
TC up to 180 K

43. Making DMS ferromagnetic – p-type doping
valence band holes mediate ferro
coupling in p-type DMS
source of holes in Mn-based DMSs, x < 10%:
Mn itself III-V
(In,Mn)As; (Ga,Mn)As H. Ohno et al. [IBM, Tohoku] PRL’92, APL’96
(Sb,Mn)2Te3; (Bi,Mn)2Te3 Choi et al. [Ulsan] pps(b)’04
acceptor impurities
(Cd,Mn)Te:N, (Zn,Mn)Te:P
TD, Cibert et al. [Grenoble, Warsaw] PRB’97, PRL’97, PRL’03
(K,Ba)(Zn,Mn)2As2 et al. [Beijing, Columbia U.] Nat. Commun.’13
cation vacancies IV-VI, [I-II]-V
(Pb,Sn,Mn)Te T. Story et al. [Warsaw] PRL’86
(Ge,Mn)Te Y. Fukuma et al. [Yamaguchi] APL’08
[Li(Zn,Mn)]As Z. Deng et al. [Beijing, Columbia,Tokyo, Vancouver] Nature Comm.’11
TC up to 190 K
TC up to 20 K
TC up to 5 K
TC up to 50 K
TC up to 10 K
TC up to 180 K

44. TC in p-type (III,Mn)V p-d Zener model/expl.
T.D. et al., Science’00
InSb: T. Jungwirth et al., PRB’02
Berkeley
Prague/Nottingham/Beijing
Kanagawa
Tohoku
Notre Dame

45. High TC ferromagnetic semiconductors

46. wz-c-(Ga,Mn)N, (Ga,Fe)N, (In,Mn)N, (Al,Mn)N, (Ga,Cr)N, (Al,Cr)N
DMS, DMO, and non-magnetic materials showing spontaneous magnetization at 300 K
wz-c-(Ga,Mn)N, (Ga,Fe)N, (In,Mn)N, (Al,Mn)N, (Ga,Cr)N, (Al,Cr)N
(Ga,Mn)As, (In,Mn)As, (Ga,Mn)Sb, (Ga,Mn)P:C
(Zn,Mn)O, (Zn,Ni)O, (Zn,Co)O, (Zn,V)O, (Zn,Fe,Cu)O, (Zn,Cu)O
(Zn,Cr)Te
(Ti,Co)O2, (Ti,V)O2, (Ti,Cr)O2, (Sn,Co)O2, (Sn,Fe)O2, (Hf,Co)O2
(Cd,Ge,Mn)P2, (Zn,Ge,Mn)P2, (Cd,Ge,Mn)As2, (Zn,Sn,Mn)As2
(Ge,Mn), (Ge,Cr), (Ge,Mn,Fe), (Si,Fe), (Si,Mn), (SiC,Fe)
(La,Ca)B6, CaB2C2, C, C60, HfO2, ZnO, GaN:Gd, GaN:Eu...
holes unnecessary
TM ions unnecessary
confirmed by ab initio works in many cases
properties strongly dependent on the growth conditions

47. Functionalities

48. Magnetically-doped semiconductors - functionalities
Localized gap states
cf. Hannes Raebiger – ab initio
-- carrier trapping (TM gap levels, Zhang-Rice polarons)
 semi-insulating substrates GaAs:Cr, InP:Fe, GaN:Fe, …

49. Magnetically-doped semiconductors - functionalities
Localized gap states
-- carrier trapping (TM gap levels, Zhang-Rice polarons)
 semi-insulating substrates GaAs:Cr, InP:Fe, GaN:Fe, …
-- intra-center optical transitions
 LEDs ZnSe:Mn
 broad band optically pumped lasers oxides: TM, ZnSe:Cr, ...
S. Mirov et al..
Laser & Photon. Rev.
4, No. 1, 21–41 (2010)
Challenge: electrically pumped broadband lasers

50. Optical insulators of DMS
absorption (+) > (-)  magnetic circular dichroism
 large Faraday rotation
optical isolators:
J. Gaj, M. Nawrocki, R. Gałązka SSC’78
laser
(Cd,Mn)Te
magnet
fiber
F = /4
spintronic device
Challenge: optical isolators of ferromagnetic semiconductors

51. Functionalities of ferromagnetic insulators
Spin filtering tunneling barriers
Spin current leads via magnons
Split topological surface and edge states ….

52. Functionalities of hole-mediated ferromagnets Controlling magnetization direction by an electric field
low-power
magnetization
switching
Chiba et al. [Tohoku, Warsaw] Nature’08

53. Functionalities of hole-mediated ferromagnets Controlling magnetization direction by an electric field
physics:
repopulation of v.b.
subbands affects
holes’ L and via s.o. s
low-power
magnetization
switching
D. Chiba et al. [Tohoku, Warsaw] Nature’09

54. Uniaxial in-plane magnetic anisotropy – p-d Zener modeling
J. Zemen et al. [Prague] PRB'09, Birowska et al. [Warsaw] PRL’12
W. Stefanowicz et al. [Warsaw, Regensburg] PRB‘10

55. Summary Three families of ferromagnetic DMSs
-- high temperature ferro DMSs, DMOs, TC up to 900 K
-- dilute ferromagnetic insulators, TC up to 15 K
superexchange
-- carrier-mediated ferromagnetic DMSs, TC up to 190 K
p-d Zener model

56. Outlook Unanticipated richness of materials science challenges
Test beds for spintronic functionalities

57. Outlook Unanticipated richness of materials science challenges
Test beds for spintronic functionalities
Challenge:
understanding and functionalizing high TC in semiconductors
aggregation of TM ions?
d0 ferromagnetism?
contamination? ….

58. Outlook Challenge: how to go to 300 K with proven functionalities
Unanticipated richness of materials science challenges
Test beds for spintronic functionalities
Challenge:
how to go to 300 K with proven functionalities

59. Y. Siota et al. [Osaka, Tohoku] Nature Mater.2012
Outlook
Unanticipated richness of materials science challenges
Test beds for spintronic functionalities
Challenge:
how to go to 300 K with proven functionalities
increasing TM/hole concentrations [e.g. (Si,Mn)]
ferrimagnetic oxide spinels, TC up to 800 K
ferromagnetic metals, TC up to 1200 K
condensed magnetic semiconductors
-- exploiting attractive forces between TM cations
antiferromagnetic spintronics
 no cross-talking between bits
 can be switched by electric current
cf. Andrei Zenkevich
Y. Siota et al. [Osaka, Tohoku] Nature Mater.2012

60. Magnetoresistance hysteresis n-Zn1-xMnxO:Al, x = 0.03D
50mK
60mK
75mK
100mK
125mK
150mK
200mK
TC = 160 mK
Rxx ()
D (mT)
Magnetic field (T)
Temperature (K)
M. Sawicki, ..., M. Kawasaki, T.D., ICPS’00

61. Replacing lithography by self-assembling
top-down  bottom up
nanocomposites assembled with atomic precision

63. Nanospintronics Nanoelectronics =
manipulation with charges and
currents at nanoscale
Nanospintronics = manipulations with magnetisation and spin currents at nanoscale

64. Universal memory – STT MRAM
scalable
nonvolatile > 10 yr
fast ~ ns
endurable 1015
radiation hardness
Will replace HD
and SSD (flash)?

65. Low-power logic-in-memory
CoFeB Ru
MgO
ferromagnetic
MTJ
semiconductor
CMOS
4 MTJs + 32 MOSs
Adder:
power consumption
reduced 4 times
S. Matsunaga et al. (Tohoku) APEX’08