Tuning the perpendicular magnetic anisotropy of CoCr layers in multilayered systems
The
combination
of
Pt
with
Co
either
in
alloy
or
in
multilayer
form
is
widely
studied
among
the
potential
magnetic
media
for
ultrahigh
density
magnetic
recording.
On
the
other
hand
the
combination
of
Co
with
Cr
in
alloy
form
is
currently
providing
commercial
magnetic
media.
In
an
effort
to
further
exploit
and
benefit
from
both
systems,
we
fabricated
Co
1-x
Cr
x
/Pt
multilayers
with
two
adjustable
parameters.
The
first
one
is
the
Cr
concentration
on
CoCr
layer
(x
=
0,
0.05
0.30),
which
modulates
segregation
effects
on
Co
grains,
thus
tunes
macroscopic
magnetic
features
such
as
saturation
magnetization
and
coercive
field.
The
second
one
is
the
small
layer
thickness
(<6
nm)
that
affects
interlayer
coupling,
perpendicular
magnetic anisotropy and magnetization enhancement through spin polarization of Pt atoms in a ferromagnetic environment.
Research
In this page you may find info for my research interests
Makis Angelakeris
Personal WebPage
Topics
Synthesis of metallic (mainly magnetic) and semiconductor thin films, multilayers and nanoparticles
Structural, magnetic, electric, magneto-optic characterization of magnetic nanostructures
Activities
My research activities include growth, structural and electronic properties of magnetic nanostructures.
Since 1995, (during my PhD thesis) I was involved in magnetic multilayer fabrication and electronic properties of them.
By
the
end
of
my
PhD
studies
(since
2000)
I
am
involved
in
magnetic
nanoparticle
projects,
participating
in
synthesis
via
physical
and
chemical
methods
and
property
characterization.
More recently, I also work on magnetic field hyperthermia in colloids and cell cultures and its correlation with structural, morphological and magnetic features.
This expertise is exploited in the optimization of collective magnetic features in a wide range of biomedical applications focusing on magnetically activated cancer treatments.
Highlights
The effect of composition and structural ordering on the magnetism of FePt nanoparticles
Spherical
4
nm
FePt
nanoparticles
were
synthesized
by
the
simultaneous
decomposition
of
Fe(CO)
5
and
the
polyol
reduction
of
Pt(acac)2.
The
final
Fe-to-Pt
composition
was
tuned
between
15
-
55
at.%
by
varying
the
ingredient
precursor
ratios.
Structural
ordering
is
promoted
in
all
cases,
though
samples
approximating
equiatomic
Fe/Pt
ratios
eventually
transform
to
fct-FePt
phase
while
the
FePt3-phase
is
favored
for
the
Pt-richer
samples.
Consequently,
the
magnetic
features
of
the
annealed
nanoparticles
may
be
categorized;
the
hard
magnetic
FePt
region
dominating
for
Fe
content
between
40
-
55
at.%
and
the
soft
magnetic
FePt3
region
dominating
in
the
region
20
-
30
at.%
while
Fe
content
less
than
20
at.%
results in Pt-richer phases with diminishing ferromagnetic behavior.
Pt-Co Multilayers: Interface Effects at the Monolayer Limit
Structural,
magnetic
and
spectroscopic
magneto-optical
features
of
Pt-Co
multilayers
prepared
by
e-beam
evaporation
are
studied.
In
order
to
examine
interface
and
induce
magnetism
effects,
the
layer
thickness
was
always
kept
under
4
monolayers
as
to
form
a
hybrid
structure
between
alloys
and
the
conventional
multilayers.
X-ray
diffraction
spectra
revealed
the
multilayer
nature
of
the
samples
while
magnetometry
measurements
recorded
tuneable
perpendicular
magnetic
anisotropy
and
enhanced
magnetization
values
due
to
the
high
degree
of
Pt-
polarization
in
a
ferromagnetic
environment.
The
experimental
technique
that
allows
one
to
study
the
small
induced
magnetism
is
the
X-ray
magnetic
circular
dichroism
(XMCD)
which
provides
quantitative
information
on
spin
and
orbital
magnetic
moments
of
the
absorbing
atom
in
both
amplitude
and
direction.
XMCD
experiments
were
performed
at
ESRF
on
the
ID12
beamline
at
Pt
L
2,3
-edges
where
enhanced
Pt
contribution on the perpendicular anisotropy was evidenced.
Critical radius for exchange bias in naturally oxidized Fe nanoparticles
Monodisperse
Fe
nanoparticles
prepared
by
thermal
decomposition
were
readily
oxidized
on
exposure
to
air.
The
resulting
nanocrystals
have
been
identified
as
inverse
spinels,
with
the
γ-Fe
2
O
3
as
the
dominant
phase
of
the
small
5
nm
iron
oxide
nanocrystals,
while
the
proportion
of
the
Fe
3
O
4
component
gradually
increases
with
particle
size.
The
small
particles’
volume
resulted
in
finite
size
effects
i.e
the
magnetization
deviates
from
the
T
3/2
Bloch's
law.
High
field
irreversibility
and
shifted
hysteresis
loops
after
field
cooled
processes
have
been
detected,
and
attributed
to
a
low
temperature
surface
spin-glass
layer.
Moreover,
there
is
a
critical
diameter, below which the surface spin-glass behaviour and exchange bias effect abruptly disappear.
Αpplication of magnetic nanoparticles as magnetic hyperthermia agents
In
this
project
we
study
the
heating
efficiency
of
magnetic
nanoparticles
and
their
application
for
magnetic
hyperthermia
on
cancer
cells.
Firstly,
structural,
morphological
and
magnetic
characterization
schemes
were
performed
to
determine
crucial
factors
for
optimizing
their
heating
potential,
such
as
size,
polydispersity,
saturation
magnetization,
coercivity.
In
an
effort
to
simulate
the
in
vivo
environment
of
animal
tissue
phantoms
and
study
the
thermal
heating
effects
resulting
from
Brownian
motion
and
hysteresis
losses,
nanoparticles
at
various
concentrations
were
embedded
in
aqueous
media
of
varying
agar
concentration.
During
the
in
vitro
application
cancer
and
normal
cell
lines
were
incubated
with
magnetic
nanoparticles
adequately
functionalized.
The
heating
profile
of
the
particles
as
studied
in
different
concentrations
and
in
correlation
with
their
potential
cytotoxicity.
Our
results
revealed
concentration
dependent
cytotoxicity
profile
and
uptake
efficiency
together
with
variable
specific
loss
power
values
yet
with
fast
thermal response, opening novel pathways in material selection as hyperthermia agents.
Layer-resolved magnetic moments in Ni/Pt multilayers
Ni
n
/Pt
m
multilayers
have
been
prepared,
characterized
via
x-ray
diffraction,
electron
microscopy,
and
magneto-optic
spectroscopy
and
SQUID
magnetometry.
Numbers
of
monolayers
in
each
multilayer
period,
n
and
m
ranged
between
2
and
13.
The
structural
studies
have
revealed
negligible
interdiffusion
and
excellent
modulation
sequences.
The
magnetic
moments
in
Ni
n
/Pt
m
multilayers
are
thoroughly
studied
by
combining
experimental
and
ab
initio
theoretical
techniques.
SQUID
magnetometry
probes
the
samples’
magnetizations.
X-ray
magnetic
circular
dichroism
separates
the
contribution
of
Ni
and
Pt
and
provides
a
layer-resolved
magnetic
moment
profile
for
the
whole
system.
The
results
are
compared
to
band-structure
calculations.
Induced
Pt
magnetic
moments
localized
mostly
at
the
interface
are
revealed.
No
magnetically
“dead”
Ni
layers
are
found.
The
magnetization
per
Ni
volume
is
slightly enhanced compared to bulk NiPt alloys.
Ag/Co multilayers: From film growth to GMR sensor
The
Ag-Co
system
either
in
multilayer
or
in
granular
alloy
form
exhibits
the
GMR
(Giant
MagnetoResistance)
effect.
By
adjusting
the
modulation
parameters
an
intermediate
structure
may
be
formed
offering
new
possibilities
for
magnetoelectronic
applications.
This
structure
resides
in
the
limit
between
multilayers
and
granular
alloys
and
is
called
granular
multilayer.
The
dependence
of
GMR
values
on
the
individual
layer
thickness
and
on
the
total
film
thickness
was
parameterised
and
magnetoresistance
values
of
16%
at
300
K
and
36%
at
30
K
were
achieved.
The
outcome
of
this
study
is
the
fabrication
of
a
two-dimension
magnetic
field
sensor
consisting
of
8
specific
elements
forming
a
2x4
array.
The
sensor
is
specialised
in
small
magnetic
field
regions
while
its
response
was
found
quite
satisfactory
regarding
its
uniformity
and
repeatability.
The
sensor
may be upgraded to larger arrays and to three dimensions in order to fulfil various market needs.
Projects (more info on http://magnacharta.physics.auth.gr & http://multigr.physics.auth.gr)
1.
CLA-Horizon-2022:Supple Graphene Bio-Platform for point-of-care early detection and monitoring of Alzheimer’s Disease (10/2023-09/2026)
2.
CSA-Horizon2020: Magnetic Nanohybrids for Cancer Therapy (09/2019- 03/2023)
3.
ESPA:EDBM34: Exploitation of field effects on adequate nanoparticle carriers for modern biomedical applications (06/2018-09/2019)
4.
ELIDEK: Magnetic Nanoparticle Arrays: Growth, Properties, Applications (8/2017-04/2018)
5
.
IKYDA:
Greek
German
collaboration:
Tuning
magnetism
in
shape-controlled
hybrid
nanoparticles
for
enhanced
hyperthermia
efficiency
and
heat-activated
drug
delivery
(2012-2013)
6.
Thales: ESF & NSRF Resarch Funding Program: “Smart” Magnetic nanoparticles probes for magnetic Resonance Imaging(MRI) (2011-2015)
7.
RTN network: Synthesis and Orbital Magnetism of core-shell nanoparticles (2004-2008)
8.
PENED: Ordered arrays of magnetic nanoparticles for technological applications (2005-2008)
9.
NATO Science Program: Novel magnetic nanostructures for sensor fabrication (2004-2006)
10.
EPEAEK II: Correlation of structure and Magnetism in novel magnetic nanostructures (2002-2005)
11.
Greek-French Collaboration: Novel magnetic nanostructured materials for high-resolution magnetic sensors (2003-2005)
12.
RTN Network: Correlation of structure and magnetism in novel nanoscale magnetic particles (2000-2004)
13.
HCM Network :Magnetic and Transport properties of novel mesoscopic magnetic thin films and multilayers (1995-1998)
14.
EPET II: GMR Sensors for magnetic field recording (1995-1998)
15.
GSRT: Magneto-Optic study of artificially modulated magnetic superlattices (1994-1997)
16.
BRITE/EURAM: Multilayered Magnetic Materials: Fundamental and Technological Aspects (1990-1994)
