Tailoring Magnetic Anisotropies in Ferromagnetic Semiconductors

Tailoring magnetic anisotropies
in ferromagnetic semiconductors
Konrad Dziatkowski
1st Erasmus Intensive Program Spintronics and Applications 1

Outline
1. Magnetic anisotropy – concept
2. Spintronics
3. Dilute Magnetic Semiconductors
4. Magnetic anisotropy – phenomenology and measurements
5. Examples of MA in DMSs
Aim: understanding of experimental data on magnetic anisotropy

Outline
2. Spintronics

Magnetic anisotropy
dependence of magnetic properties on the orientation of external magnetic field
http://photon-science.desy.de

Magnetic anisotropy
http://roma2.rm.ingv.itsusceptibility
dependence of magnetic properties on the orientation of external magnetic field

Magnetic anisotropy
sample shape
shape (demagnetization) anisotropy
http://ocw.mit.edu
http://www.physics.mcmaster.ca http://www.nanowerk.com
http://www.nanowerk.com http://www.technologyreview.com
crystal structure
magnetocrystalline anisotropy
dependence of magnetic properties on the orientation with respect to what?

Ferromagnetism
long-range ferromagnetic ordering
other types of order
antiferromagnet
ferrimagnet
http://physics.tutorvista.com
H = 0, M ≠ 0
dependence of magnetic properties on the orientation of what?

Inter-spin interactions
exchange interaction
dipol-dipol interaction

Magnetic anisotropy and magnetic interactions
shape anisotropy
dipol-dipol interaction: long range, directional

exchange interaction: short range, isotropic
X

http://www.nature.com
magnetocrystalline
anisotropy
spin-orbit interaction

Keyword summary – part I
dependence on orientation
shape anisotropy
long range ferromagnetic ordering

Outline
2. Spintronics

Spintronics (spin-based electronics)
a field of electronics involving nanoscale devices in
which the information is carried/stored with use of the
spin of an electron rather than its electric charge
magnitude of passed current is modulated by the relative
orientation of the magnetization in ferromagnetic films
P. A. Gruenberg, Rev. Mod. Phys. 80, 1531 (2008)
A. Fert, Rev. Mod. Phys. 80, 1517 (2008)

Magnetic RAM
Everspin
Technologies
Spin FET
http://www.electroiq.com

knowing and understanding magnetic anisotropy
is fundamental in designing and manufacturing
of spintronic devices
metal-based spintronics
(magnetoelectronics)
http://pnas.org
integration of computational
and storage functionalities
all-semiconductor
spintronics

Keyword summary – part II
further integration of devices
control of magnetization
all-semiconductor spintronics

Outline
2. Spintronics

Dilute Magnetic Semiconductors
alloys of parent, nonmagnetic semiconductor (e.g. GaAs, CdTe) with the
atoms of magnetic elements (e.g. Mn, Co)
host materials:
III-V: GaAs, GaP, GaN, AlAs, AlN, InAs, InN, InP, ...
II-VI: CdTe, CdSe, CdS, ZnTe, ZnS, PbTe, ...
IV: Ge, Si
magnetic dopants:
Mn, Cr, Fe, Co, ... http://www.ohno.riec.tohoku.ac.jp

Ferromagnetic DMSs
(Ga,Mn)As * (In,Mn)As * (Ga,Mn)N * (Zn,Mn)O * (Zn,Co)O * ...
(Ga,Mn)As exhibits the highest Curie temperature: 170 ~ 190 K
L. Chen et al., Appl. Phys. Lett. 95, 182505 (2009)
H. Ohno, J. Appl. Phys. 113, 136509 (2013)
HL. Wang et al., Sci China-Phys Mech Astron 56, 99 (2013)
A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010)
K. Y. Wang et al., AIP Conf. Proc. 772, 333 (2005)

Ferromagnetic (Ga,Mn)As
low temperature molecular beam epitaxy + post growth annealing
after: H. Ohno, J. Magn. Magn. Mater. 200, 110 (1999)
http://unix12.fzu.cz

Ferromagnetic (Ga,Mn)As
http://unix12.fzu.cz
reduction of:
>> magnetization
>> concentration of holes
>> Curie temperature
• substitutional manganese MnGa
>> electronic configuration: 3d5
>> acceptor
>> Bohr magnetons per ion: 5
• interstitial manganese
>> double donor (electric compensation)
>> antiferromagnetic coupling with substitutional
manganese (magnetic compensation)
• antistructural defect AsGa
>> native for LT-MBE

Ferromagnetism of (Ga,Mn)As
exchange interaction between band holes and manganese ions
band holes
of p shell
localized electrons from
d shell of Mn ions
Jpd < 0
T. Jungwirth et al., Rev. Mod. Phys. 78, 809 (2006)
S. Ohya et al., Nature Physics 7, 342, (2011)

Ferromagnetism of (Ga,Mn)As
exchange interaction between band holes and manganese ions
band holes
of p shell
localized electrons from
d shell of Mn ions
Jpd < 0
T. Jungwirth et al., Rev. Mod. Phys. 78, 809 (2006)
effective RKKY-like interaction between manganese ions
F. Matsukura et al., Phys. Rev. B 57, R2037 (1998)
ferromagnetic Mn-Mn coupling

Keyword summary – part III
non-magnetic host + magnetic dopants
substitutional Mn
interstitial Mn
LT-MBE + annealing
acceptor
double donor
hole-mediated ferromagnetism

Outline
2. Spintronics

Phenomenology of MA
Landau – Lifshitz – Gilbert equation
precession damping
L. Berger, Phys. Rev. B 54, 9353 (1996)
J.C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)
other torques

Phenomenology of MA
M. Farle, Rep. Prog. Phys. 61, 755 (1998)
shape
Zeeman
structure
for uniform field
for thin layer
for fct
magnetization free energy

Magnetization easy axis
energetically favorable direction of spontaneous magnetization
minimum of magnetization free energy

Experimental methods
SQUID magnetometry
DC DC + mcrowaves
Ferromagnetic resonance (FMR)
other techniques: vibrating sample magnetometry, magnetotransport,
polarized neutron reflectometry, magneto-optical Kerr effect, ...

http://photon-science.desy.de
SQUID magnetometry
DC

DC + mcrowaves
Ferromagnetic resonance (FMR)

SQUID magnetometry
T. Hentschel et al., J. Phys. D: Appl. Phys. 45, 055002 (2012)
EAHA
V. Z. C. Paes et al., J. Phys.: Condens. Matter 25, 046003 (2013)
easy axis = lowest field needed for saturation

Ferromagnetic resonance
EA
HA
http://www.intechopen.com
easy axis = minimum of resonance field

Keyword summary – part IV
free energy of magnetization
magnetometry
magnetization easy axis
ferromagnetic resonance
LLG equation
minimum of resonance field

Outline
2. Spintronics

Out-of-plane anisotropy
uniaxial shape anisotropy
shape for thin layer
in-plane EA
or easy plane
K. Dziatkowski et al., Phys. Rev. B 70, 115202 (2004)

in-plane EA perpendicular EA
X. Liu et al., Phys. Rev. B 67, 205204 (2003)

X. Liu et al., Phys. Rev. B 67, 205204 (2003)

in-plane EA perpendicular EA
growth-related uniaxial magnetocrystalline anisotropy
shape
structure
for thin layer
for fct
http://www.ohno.riec.tohoku.ac.jp

M. Sawicki, J. Magn. Magn. Mater. 300, 1 (2006)
(perpendicular) Spin Reorientation Transition
samples with low holes concentration

In-plane anisotropy
structure for fct
T. Wosinki et al., Physica E 51, 128 (2013)K. Dziatkowski et al., Phys. Rev. B 70, 115202 (2004)
biaxial + (in-plane) uniaxial
M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012) anisotropy of Mn-Mn pair energy

In-plane anisotropy
K. Dziatkowski et al., Phys. Rev. B 70, 115202 (2004)
(in plane) Spin Reorientation Transition

dependence on RF field
orientation
Atomic-steps-induced anisotropy
K. Dziatkowski et al., J. Appl. Phys. 109, 07C301 (2011)

partial strain relaxation
Strain-engineered anisotropy
F. Hoffmann, Ph.D. Dissertation, U. of. Regensburg

partial strain relaxation, shape anisotropy

shape anisotropy

Exchange bias
proximity effects
K. Dziatkowski et al., Appl. Phys. Lett. 88, 142513 (2006)
K. Dziatkowski et al., Acta Phys. Polon. A 110, 319 (2006)
unidirectional anisotropy

six-fold symmetry
Nanocomposites
(Ga,Mn)As with MnAs clusters
T. Hartmann et al., Physica E 13, 572 (2002)

Keyword summary – part V
biaxial strain
uniaxial out-of-plane anisotropy
uniaxial in-plane anisotropy
spin reorientation transition

Thank you!
biaxial strain
uniaxial out-of-plane anisotropy
uniaxial in-plane anisotropy
spin reorientation transition
dependence on orientation
shape anisotropy
long range ferromagnetic ordering
further integration of devices
control of magnetization
all-semiconductor spintronics
non-magnetic host + magnetic dopants
substitutional Mn
interstitial Mn
LT-MBE + annealing
acceptor
double donor
hole-mediated ferromagnetism
free energy of magnetization
magnetometry
magnetization easy axis
ferromagnetic resonance
LLG equation
minimum of resonance field

Tailoring Magnetic Anisotropies in Ferromagnetic Semiconductors

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Tailoring Magnetic Anisotropies in Ferromagnetic Semiconductors