Slide title here

1
Current Nanospin related theory topics in
Praguein collaboration with Texas and
Warsawbased primarily on Nottingham and Hitachi
experimental activities
2

• Range of materials or model systems
• 2D models with simple Rashba
• spin-orbit coupled bands

• Dilute-moment ferromagnetic
• semiconductors
• still simple bands yet strongly
• exchange and SO split
• dilute moment tunable,
• weak dipolar fields, smaller
• STT currents

• Systems with complex bands
• but room Tc FeNi, CoFe, CoPt,.

3

• Technical issues
• Analytical calculations (Rashba model)
• k.p semiphenomenological modelling (typical
  for semiconductors)
• extensive library of home-made routines
• spd-tight-binding modelling (half way
  between phenomenological and ab initio)
• home-made codes
• Full ab initio heavy numerics (transition
  metals based structures)
• standard full-potential libraries,
  home-made relativistic ab-initio codes
• Conclusions derived from bulk band structures
• total energy calculations, Boltzmann and
  Kubo transport equations
• Device specific modeling
• Landauer-Buttiker formalism

4
Extraordinary magnetoresistance (AHE/SHE, AMR,
STT)
Ordinary magnetoresistance response in normal
metals to external magnetic field via classical
Lorentz force
Extraordinary magnetoresistance response to
internal magnetization in ferromagnets via
quantum-relativistic spin-orbit coupling
B
_ _ _ _ _ _ _ _ _ _
_
FL

I
or anisotropic magnetoresistance
V
e.g. ordinary (quantum) Hall effect
5
Intrinsic vs. extrinsic AHE in Rashba 2D systems
Solvable analytically
skew scattering
side jump
intrinsic
group velocity
semicalssical Boltzmann eq.
distribution function
quantum Kubo formula
jump
side
int.
skew
sc.
6
skew scattering term - absent in 2DEG for
two-band occupation - absent in 2DHG for any
band occupation

• extenting the study to
• 4-band spherical Kohn-Luttinger model

spherical K-L model
Rashba
- full 6(multi)-band model of DMSs
- ab initio band structures of metals
Proposed experimental setup
so far microscopic calculations of intrinsic AHE
only in these systems
7
Origin of non-crystalline and crystalline AMR in
GaMnAs
Boltzmann eq. in relax. time approximation
1st order Born approximation
4-band spherical Kohn-Luttinger model
SO-coupling spherical model
FM exchange spiitting
M
1/?k (M)
(k . s)2
Mx . sx
ky
kx
M
hot spots for scattering of states moving ? M ?
R(M ? I)gt R(M I)
ky
kx
8
full 6-band Hamiltonian non-crystalline
and crystalline AMR
spherical model non-crystalline AMR only
theory

• explains sign of non-crystalline AMR
• consistent with experimentally seen
• increasing role of crystalline terms with
• increasing compensation
• large AMR dominated by crystalline terms
• in ultrathin layers not explained by bulk
  theory

exp.
9

• Ferromagnetism mediated by As p-orbital-like band
  states
• basic SO coupling related symmetries similar to
  familiar GaAs, unchanged by MnGa
• carriers with strong SO coupling and exchange
  splitting due to hybridization with MnGa
  d-orbitals

• straightforward means for relating intuitive
  physical pictures with microscopic calculations
• compare with ferro metals model of scattering
  of non-SO-coupled non-exchange-split s-state
• carriers to localized d-states ? difficult to
  match with ab initio theories with mixed s-d
  carriers

10
Strain and doping-depent magnetocrystalline
anisotropy
macroscopic elastic theory simulations of strains
GaMnAs
microscopic magneto- crystalline anisotropies
11
New device functionalities and new opportunity
for exploring the rich phenomenology of
magnetocrystalline anisotropies in (Ga,Mn)As
12
Close relatives to GaMnAs with new degrees of
freedomn-type DMSs, higher Tc,
III I II ? Ga Li Zn

• GaAs and LiZnAs are twin semiconductors

• Prediction that Mn-doped are also twin
  ferromagnetic semiconductors

• No limit for Mn-Zn (II-II) substitution
• Independent carrier doping by Li-Zn
• stoichiometry adjustment

Limited confidence in ab initio calc. Reasonable
confidence when comparing to GaMnAs bench-mark
material
13
Electron mediated Mn-Mn coupling in n-type
Li(Zn,Mn)As similar to hole mediated coupling
in p-type (Ga,Mn)As
Tc
14
Family of I-II-V hosts
15

• theoretical exploration of I-II-Vs ? I-Mn-Vs
  ? I-(II,Mn)V DMSs
• MOCVD growth of the most promising theory
  candidates
• MBE growth to achieve better stoichiometry
  control for the promising MOCVD materials

16
MnI formation in mixed (Al,Ga)As and Ga(As,P)
higher in (Al,Ga)As and Ga(As,P) than in GaAs
smaller interstitial space only in Ga(As,P)
Less interstitials in Ga(As,P) more interstitials
in (Al,Ga)As
17
n-type AlAs with int. Mn only
electrons can mediate FM coupling for both
subst. and int. Mn
Comparable Tc to n-type hosts with substitutional
Mn moments