Anisotropic magnetoresistance effects in ferromagnetic semiconductor and metal devices

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Anisotropic magnetoresistance effects in
ferromagnetic semiconductor and metal devices
Tomas Jungwirth
University of Nottingham
Bryan Gallagher, Tom Foxon, Richard
Campion, Kevin Edmonds, Andrew
Rushforth, Chris King et al.
Institute of Physics ASCR Alexander Shick,
Jan Mašek, Josef Kudrnovský, František Máca,
Karel Výborný, Jan Zemen, Vít Novák, Kamil
Olejník, et al.
Hitachi Labs., UK Japan
University of Texas and Texas
AM Jorg Wunderlich,
Byong-Guk Park, Andrew Irvine,
Allan MacDonald, Jairo Sinova David Williams,
Akira, Sugawara, et al.

University of Wuerzburg Polish
Academy of Sciences Tohoku University
Laurens Molenkamp,
Charles Gould Tomasz Dietl, et al.
Hideo Ohno, et al.




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• Outline
• 1. Intro - basic micromagnetics in DMSs
• 2. DMS materials science
• 3. AMR effects in DMSs and metals devices and
  physics

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(Ga,Mn)As an archetypical dilute moment FM
semiconductor
As-p-like holes
SW-transf. ? Jpd SMn . shole
Mn-d-like local moments
Dilute Mn-doped SC sensitive to doping
100?smaller Ms than in conventional metal FMs
Mn-Mn coupling mediated by holes in SO-coupled SC
valence bands sensitive to gating, comparable
magnetocrystalline anisotropy energy and
stiffness to metal FMs
For not too strong p-d hybridization kinetic-exch
ange (Jpd) host SC bands provides simple yet
often semiquantitative description
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MF-like M(T) square hysteresis loops
1 mm
500 nm
22 K
8 K
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One
Strain controlled micromagnetics and current
induced DW dynamics ? tunable 100x smaller
critical currents than in metals
0.1-1 ?m
Huge hysteretic MR tunable by gate due to CBAMR
? spintronic transistor
plus weak dipolar crosslinks ? prospect for
dense integration of magnetic microelements
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• Outline
• 1. Intro - basic micromagnetics in DMSs
• 2. DMS materials science
• 3. AMR effects in DMSs and metals devices and
  physics

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Magnetism in systems with coupled dilute moments
and delocalized band electrons
(Ga,Mn)As
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GaAs VB
GaAsMn extrinsic semiconductor
Mn-acceptor level (IB)
GaMnAs disordered VB
2.2x1020 cm-3
VB-IB
VB-CB
?
?
Short-range M . s potential - additional
Mn-hole binding - ferromagnetism - scattering
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MIT in GaAsMn at order of magnitude higher
doping than quoted in text books
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MIT in p-type GaAs - shallow acc. (30meV) 1018
cm-3 - Mn (110meV) 1020 cm-3
Mobilities - 3-10x larger in GaAsC - similar in
GaAsMg or InAsMn
gt 2 Mn metallic but strongly disordered
? ? Mn spacing
Model SO-coupled, exch.-split Bloch VB
disorder - conveniently simple and increasingly
meaningful as metallicity increases - no better
than semi-quantitative
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MnGa solubility limit
Covalent SCs do not like doping?
self-compensation by interstitial Mn
Interstitial MnInt is detrimental to magnetic
order charge and moment compensation defect
Can be annealed out Tc 95K in as-grown (9 Mn) to
173 in annealed (6 Mnsub) but MnGa lt nominal Mn
theory exp.
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Delocalized holes long-range coupl.
Weak hybrid.
Search for optimal III-V host optimal
combination of hole delocalization, p-d coupling
strength, low self-compensation
InSb, InAs, GaAs
d5
Impurity-band holes short-range coupl.
Strong hybrid.
GaP, AlAs
d 5 ? d 4
no holes
d
GaN
d4
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I-II-Mn-V ferromgantic semiconductors
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

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• Outline
• 1. Intro - basic micromagnetics in DMSs
• 2. DMS materials science
• 3. AMR effects in DMSs and metals devices and
  physics

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Anisotropic, SO-coupled, exchange-split hole
bands
Chemical potential ? CBAMR
M
Tunneling DOS ? TAMR
M
I
Impurity scattering rates ? AMR
I
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Coulomb blockade AMR anisotropic chemical
potential
Q
VD
Source
Drain
Gate
VG
magnetic
electric
control of Coulomb blockade oscillations
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Worth trying to look for CBAMR in SO-coupled
room-Tc metal FMs

• CBAMR if change of ??(M) e2/2C?
• In our (Ga,Mn)As meV ( 10 Kelvin)
• In room-T ferromagnet change of ??(M)100K
• Room-T conventional SET
• (e2/2C? gt300K) possible

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Tunneling AMR anisotropic TDOS
TAMR in GaMnAs
Anisotropc tunneling amplitudes
1-10 in metallic GaMnAs
Huge when approaching MIT in GaMnAs
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TAMR in metals
theory
experiment
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Anisotropic magnetoresistance
Semiquantitative numerical understanding in GaMnAs
THEORY
EXPERIMENT
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Qualitative physical (analytical) picture
anisotropic scattering
SO polarized scatterers
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