the effect of intentional alloying in the magnetism of xpt (x fe...

The effect of intentional alloying The effect of intentional alloying in the magnetism

of XPt (X Fe Co) Based Nanostructuresof XPt (X=Fe, Co) Based Nanostructures

M. AngelakerisDepartment of PhysicsDepartment of Physics

Aristotle Universityof Thessaloniki

The 8th International Workshop

8th International Workshop on Synthesis and Orbital Magnetism of core-shell nanoparticles Mittelwihr, October 24-25, 2008 1

on Synthesis and Orbital Magnetism of core-shell nanoparticles

Mittelwihr, October 24-25, 2008

Outline

1.Intentional alloying at the nanoscale

2.Case studies

Multilayers

1.Pt-SmCo: Multilayer modulation vs thin film

2.Pt-Co: Interface Effects at the Monolayer Limit

3.Pt-CoCr: Adjustable perpendicular anisotropy

Nanoparticles

1.Pt-Co: Finite-size effects

2.Pt-Fe: Composition & Structural Ordering

3 O tl k & P ti


3.Outlook & Perspectives

Why magnetic nanostructures?

Intentional alloying at the nanoscale

Unique properties different from bulk materials

Why magnetic nanostructures?

Unique properties different from bulk materials

Property modulation due to size and surface/interface effects

Surface/bulk atoms ratio is large

Broken symmetry at surface/interfaceelement1

Different electronic environment / charge transfer at interfacee e e t

element2

Properties attractive for technological applications:

Ultra high density information storage

High performance magnets

Bio-applications


Bio applications

Intentional alloying at the nanoscaleFePt alloys

• Cubic crystal structure (fcc)

disordered fcc ordered fct

FePt alloys

Cubic crystal structure (fcc)– Low coercive field

– Soft magnetic phase

• Tetragonal symmetry (fct)– Coupling between Fe- and Pt- layers

a=c a≠c– Enhanced magnetocrystalline anisotropy

– Hard magnetic phase (K ~ 6.6.107 erg/cm3,

Ms ~ 1140 emu/cm3, Ha, bulk ~ 116 kOe)

a=c a≠c

• Three regions of order-disorder

transition in the phase diagram

• Chemical stability


CoPt alloys

Intentional alloying at the nanoscaleCoPt alloys

• Cubic crystal structure (fcc)disordered fcc ordered fct

y ( )– Superparamagnetic limit : 9 nm

– Soft magnetic phase

• Tetragonal symmetry (fct)– Superparamagnetic limit : 3 nm

Enhanced magnetocrystalline anisotropy

a=ca≠c

– Enhanced magnetocrystalline anisotropy

– Hard magnetic phase (K ~ 4.107 ergs/cm3,

Ms ~ 800 emu/cm3, Ha, bulk ~ 123 kOe)

– Corrosion resistance

• Two regions of order-disorder

t iti i th h ditransition in the phase diagram

• Chemical stability


Intentional alloying at the nanoscaleMotivation

• FePt and CoPt alloys are candidate materials

Motivation

for applications in high-density storage media

• The choice of synthesis method facilitates the control of the shape and size of the magnetic nanoclusters

• Investigation of structural and magnetic features of bimetallic layers and nanoparticles with various morphologies and compositions

• Post-preparation treatment (annealing) transforms the as-prepared disordered (A1) X-Pt phase to the ordered (L10, L12) phases with i d ti h t i ti


improved magnetic characteristics

Motivation: How much information is globally produced?

Intentional alloying at the nanoscaleMotivation: How much information is globally produced?

Print, film, magnetic, and optical storage Print, film, magnetic, and optical storage , , g , p g, , g , p gmedia produced ~ media produced ~ 5 exabytes5 exabytes

of new information in 2002. of new information in 2002. b ( ) 0b ( ) 01818 bb1 Exabyte (EB)= 101 Exabyte (EB)= 101818 bytes bytes

2 EB: 2 EB: Total volume of information generated in 1999.Total volume of information generated in 1999.5 EB 5 EB All words ever spoken by human beings.All words ever spoken by human beings.

1 Terabyte (TB)= 101 Terabyte (TB)= 101212 bytes bytes 1 Terabyte (TB)= 101 Terabyte (TB)= 10 bytes bytes 1 Terabyte: 1 Terabyte: 50000 trees made into paper and printed.50000 trees made into paper and printed.

2 Terabytes: 2 Terabytes: An academic research library.An academic research library.

9292%% ofof thethe newnew informationinformation waswas storedstored ononmagneticmagnetic media,media, mostlymostly inin HARDHARD DISKSDISKS3030%% increaseincrease fromfrom 19991999 tilltill 20022002

Next report: within 2008

3030%% increaseincrease fromfrom 19991999 tilltill 20022002


http://hmi.ucsd.edu/howmuchinfo.phpSponsors: AT&T, Cisco, IBM, LSI, Seagate,Oracle, Palo Alto Research Center

(PARC), UC San Diego, MIT and UC Berkeley.

[1] http://www2.sims.berkeley.edu/research/projects/how[1] http://www2.sims.berkeley.edu/research/projects/how--muchmuch--infoinfo--20032003

Current & Future Magnetic MediaIntentional alloying at the nanoscale

CoCrCoCr--X (X:Ta,Pt) based alloysX (X:Ta,Pt) based alloysHigh coercivities

Current & Future Magnetic Media

gNaturally grow in hcp structure with the required c-axis vertical

Co/Pt multilayersCo/Pt multilayersPerpendicular magnetic anisotropy when tCo < 1 nmp g pyEnhanced MagnetizationLarge Kerr rotations at short wavelengthsgood tolerance against oxidation and corrosion

FePt nanoparticlesFePt nanoparticlesUltrahigh density > 1000 Gb/in2

Magnetic stability-Post-synthetic treatment-Large scale integrationg y y g g


Outline


2.Case studies

Multilayers




Nanoparticles



3 O tl k & P ti



Pt-SmCo: Multilayer modulation vs thin filmSample Preparation

UHV e-beam evaporation - Pt, SmCo5 targets – rev=0.1 nm/s

Sample Preparation

• Τdep ~ RT, PBase~5 x10-9 mbar, Si(111)• Post deposition annealing (400-700oC )

OverlayerOverlayer PtPt

SmCoSmCo55

PtPtOverlayerOverlayer PtPt OverlayerOverlayer PtPt OverlayerOverlayer PtPt PtPtyy

Buffer layer PtBuffer layer Pt K pt n l Si

OverlayerOverlayer PtPt

Buffer layer PtBuffer layer PtSmCoSmCo55: 8 nm: 8 nm

B ff l PtB ff l Pt

Kapton-glass-Si

Buffer layer PtBuffer layer Pt

SmCoSmCo55: 1.6 nm: 1.6 nm

Kapton-glass-Si

N=20N=20Pt:1.2 nmPt:1.2 nm

SmCoSmCo55:1.6 nm:1.6 nm

Kapton-glass-Si


Characterization Techniques XRD, SEM, EDX, TEM, VSM


SmCoSmCo55:1.6 nm:1.6 nm, , , ,

Pt-SmCo: Multilayer modulation vs thin filmRole of SmCo thickness

200

1)

Pt(5 nm)/SmCo(1.6 nm)/Pt(5 nm)

Role of SmCo thickness

150

Si(1

1

PtPtSmCoSmCo

100 111 00

2

(cps

)SiPtPt

SmCoSmCo55

50

101

200

001

211

Pt(1

11)

Pt(0

02)

2)

I

50

110

Pt(0

22

20 30 40 50 60 70 80 900

2θEvidence of crystalline SmCo5 formation


Evidence of crystalline SmCo5 formation

distinct trilayer formation

Pt-SmCo: Multilayer modulation vs thin filmRole of multilayering

{Pt(1.2 nm)-SmCo(1.6 nm)}x20

Role of multilayering

600

11)

Sample SmCo5

Pt

-1

0{ ( ) ( )}

Overlayer PtSmCo

Pt(1

1

2

I (cp

s)

-1

PtPtPt

SmCoSmCoPt

Pt

300

t(002

)3 42 Si

PtPt

Pt SmCo

7 14 21 35 40 45 50 55 60 65 700

110

200

111

002

P

Pt(0

22)

+2

-2

+1

Si

7 14 21 35 40 45 50 55 60 65 702θ

Multilayer evidence

wavy interfaces –Pt diffusivity


y y

Nanocrystalline character

Pt-SmCo: Multilayer modulation vs thin filmRole of multilayering

1 0

Role of multilayering

0 5

1,0 SmCo thickness 1.6 nm 8.0 nm1.6 nm multilayer

100 Oe, 78%60 Oe, 5%350 Oe 48%

0 0

0,5

M /M

s

1.6 nm multilayer350 Oe, 48%

0 5

0,0

M

1 0

-0,5

-0,4 -0,2 0,0 0,2 0,4

-1,0

Magnetic Field (T)


In-plane anisotropy, Hc=350 Oe, Ms=1077 emu/cm3, Mrem/Ms=48%

{Pt(1 2 nm) SmCo5(1 6 nm)}x20

Pt-SmCo: Multilayer modulation vs thin filmRole of annealing

1250

{Pt(1.2 nm)-SmCo5(1.6 nm)}x20

450oC500oC

Role of annealing

1000 initial sample400oC

450 C

cm3 )PtPt

750700oC

M (e

mu/

c

SiPtPt

500

M

Annealing up to 500 oC

Si

Post-deposition

250

Annealing up to 500 oCMs, Hc, Mrem/Ms increase

Ms=1202 emu/cm3, Hc=550 Oe

annealingup to 500o C

0 0 0 2 0 40enhances

magnetization


0,0 0,2 0,4Magnetic Field (T)

magnetization

coercive field

Outline


2.Case studies

Multilayers




Nanoparticles



3 O tl k & P ti



Why monolayer limit?

Pt-Co: Interface Effects at the Monolayer Limit Why monolayer limit?

The mechanism of the strong PMA of Pt-Co multilayers isll tt ib t d t th ibl i igenerally attributed to three possible origins.

1. the interfacial anisotropy, related to the orientation ofCo/Pt layers having the largest value for the (111)Co/Pt layers, having the largest value for the (111)interfaces.

2. the CoPt alloy formation at the interface area that mayy ymodify the magnetocrystalline anisotropy.

3. in Pt, Co layers of small thickness the stress-inducedmagnetoelastic energy, which may also contribute toPMA.

In the case of multilayers crucial parameters are the Co PtIn the case of multilayers, crucial parameters are the Co, Ptlayer thickness, i.e. modulation parameters together with thenumber N of bilayers.


Structure at the monolayer limit

Pt-Co: Interface Effects at the Monolayer Limit Structure at the monolayer limit

1200

b. u

nits

)

Pt(111)

800I (ar

b Pt(111)

400Pt(7 A)-Co(2 A)

Pt(4 A)-Co(2 A)

5 10 40 45 500

Pt(4 A)-Co(4 A)

• Multilayer periodicity preserves• fcc(111) stacking due to Pt buffer layer

2θ (deg)

Sample tPt/tCo D (Å) d111(Å)

Pt(7 Å)-Co(2 Å) 3.5 120 2.2147


• fcc(111) stacking due to Pt buffer layer• Scherrer: Nanocrystallites of ø~100 Å

Pt(7 Å) Co(2 Å) 3.5 120 2.2147

Pt(4 Å)-Co(2 Å) 2.0 110 2.2075

Pt(4 Å)-Co(4 Å) 1.0 95 2.1516

Development of PMAPt-Co: Interface Effects at the Monolayer Limit

Development of PMA

1000

2000 Pt (4 A) - Co (4 A) Pt (4 A) - Co (2 A) Pt (7 A) - Co (2 A)

3 -Co)

1000

2000 Pt (4 A) - Co (4 A) Pt (4 A) - Co (2 A) Pt (7 A) - Co (2 A)

3 -Co)

0

1000

M (e

mu/

cm3

0

M (e

mu/

cm3

-1000-1000

M

-8 -4 0 4 8

-2000

H (kOe)

10 K

-8 -4 0 4 8

-2000

H (kOe)

300 K

Strong PMA for 2 Å of Co (1 monolayer)Modulation with Pt enhances PMA

H (kOe)


tPt/tCo influence

Technological featuresPt-Co: Interface Effects at the Monolayer Limit

2 0

Technological features

90

2,0

)

1,6 H (kO

em/M

s (%

)

801,2Mrem/Ms

Pt(4 A) C (4 A)

e)M

re

20

40

0,8

Pt(4 A)-Co(4 A) Pt(4 A)-Co(2 A) Pt(7 A)-Co(2 A) Hc

M /M 90% 80% H 2 1 1 kO

0 50 100 150 200 250 30020

T (K)


Mrem/Ms~90%-80%, Hc 2-1.1 kOe

Magnetization Stability

Pt-Co: Interface Effects at the Monolayer Limit Magnetization Stability

2400

Pt (4 A) - Co (2 A) Pt (7 A) - Co (2 A)

m3 -C

o)

2000

Ms

(em

u/cm

M

50 100 150 200 250 300

1600

T (K)

Smaller Co content-rapid Curie approachSpin polarization of Pt extends throughout the layer

T (K)


Spin polarization of Pt extends throughout the layerEnhancement of Co magnetization

Evidence of Pt polarization-XMCD

Pt-Co: Interface Effects at the Monolayer Limit Evidence of Pt polarization XMCD

Pt(7 Å)Pt(7 Å)--Co(2 Å)Co(2 Å)Pt(7 Å)-Co(2 Å)/ 3 L2

its) L3

• μL/μs=0.155 • μL=0.065 μΒ/atom• μ =0 42 μ /atom The magnetic moment values

1

2

(arb

. un• μs=0.42 μΒ/atom.

Spin-polarization extendsthroughout the Pt layer in

are the average ones for the whole Pt layer.

0

1

x3

D, X

AS

(g your multilayers andeventually enhancesmagnetization.

-1

0XM

CD

x3

gLiterature XMCD, XRR:Co: 1.9– 2.2 μB/atom,Pt: 0.2– 0.4 μB/atom.

11550 11600 13250 13300

Photon Energy (eV)

μB/


Isotropic XAS and XMCD spectra at 260 K for the Pt(7 Å)-Co(2 Å) multilayer measured at the Pt L3,2 edges.

Outline


2.Case studies

Multilayers




Nanoparticles



3 O tl k & P ti



Why Cr addition?

Pt-CoCr: Adjustable perpendicular anisotropy

bulk alloy CoCr1

2Reasons to add Cr into Co

Why Cr addition?

1200

cm3 )

thin fim CoCr2easo s to add C to Co

Li it d l bilit i COverlayerOverlayer PtPt

CoCrCoCr

PtPt800

MS (

emu

/ cLimited solubility in Co PtPt? ?

400

MCr:grain segregation


11F. Bolzoni et al., J. Magn. Magn. Mater. 31F. Bolzoni et al., J. Magn. Magn. Mater. 31--34 845 (1983)34 845 (1983)22F T Parker F T Parker et alet al J Appl Phys 66 5968(1989)J Appl Phys 66 5968(1989)

reduce intergranular couplingKapton-glass-Si


0 4 8 12 16 20 24 28 320

% Cr concentration

22F.T. Parker F.T. Parker et al.,et al., J. Appl. Phys. 66, 5968(1989)J. Appl. Phys. 66, 5968(1989)

Control of the magnetic properties through

lower media noisehigher coercivities

magnetically decoupled grains


Control of the magnetic properties through tailoring Cr concentrations in the multilayer:

Cr composition in the CoCr alloy: 5% & 30%

g y p g

Role of CoCr thickness


CoCo7070CrCr3030((yy nm)/Pt(nm)/Pt(0.4 0.4 nm)nm) x 30x 30

c) c)1sty = 0 3 nm

Cr 30%Cr 30%


100

quen

cy

Dav= 8.89 nm

Stan. dev. = 2.2 nm100

uenc

y

Dav = 7.27 nmStan. dev. = 1.88

2400 111

Pt(fc

c

002

Pt(fc

c1 y = 0.3 nm y = 0.3 nm y = 0.3 nm y = 1.8 nm

2 4 6 8 10 12 140

50

Freq

grain diameter (nm)2 4 6 8 10 12 140

50

Freq

u

Grain diameter (nm)1000

'0'

'0'1st1st

I (ar

b. u

nits

)

150

Dav = 7.92 nm

Stan. dev. = 1.36 nm1 5 0

y

D a v = 8 .6 8 n mS ta n . d e v .= 1 .8 2500

'0'

'0'

0

50

100

Freq

uenc

y

5 6 7 8 9 1 0 1 1 1 2 1 3 1 40

5 0

1 0 0

Freq

uenc

y

4 6 8 10 30 35 40 45 50

2θ (deg)

fcc growth-in contrast to hcp CoCrPt filmsConstant grain size 7-9 nm C l th

3 4 5 6 7 8 9 10 11 12

grain diameter (nm)

5 6 7 8 9 1 0 1 1 1 2 1 3 1 4

G ra in d ia m e te r (n m )


Columnar growth

E. Th. Papaioannou et al. Journal of Nanoscience Nanotechnology 7,1, (2007)

Role of Cr thickness

Pt-Co: Interface Effects at the Monolayer Limit

300CoCo7070CrCr3030((yy nm)/Pt(nm)/Pt(0.4 0.4 nm)nm) x 30x 30

Role of Cr thickness

200

300 0,2 y = 0.3 nm

Cr 30%Cr 30%

100

0,1

u/cm

3 -Co)

atio

n (d

eg)

-100

0 0,0

M (e

m

Ker

r rot

a

-200

-0,1

@ 10 K y = 0.6 nm

-5 0 5-300 -0,2

H (kOe)

@ 10 K


Perpendicular magnetic anisotropyPerpendicular magnetic anisotropyS =100 %, HS =100 %, Hcc = 1.5 kOe= 1.5 kOe



0,161,5

Experiment θKs

Bloch law fit

y = 0.6 nm


0,12

1,0

rota

tion

(deg

)

eld

(kO

e) CoCo7070CrCr3030((yy nm)/Pt(nm)/Pt(0.4 0.4 nm)nm) x 30x 30

0,0750,04

0,08

0,5

rr s

atur

atio

n r

Coe

rciv

e fie

15%

0 050

,

1,5

atio

n (d

eg) Experiment θKs

Bloch law fit

e)

y = 0.3 nm

0 200 400 600 800 10000,00 0,0

Ke

T t (K)

Experiment HC

Exponential fit

0%0,050

1,0sa

tura

tion

rota

cive

fiel

d (k

OeTemperature (K)

Cr 30%Cr 30%

70%

0,0250,5

Ker

r s

Coe

rc

Experiment HC

E ti l fit

Cr 30%Cr 30%ApproachApproach toto TTCC

d dd d ff


0 100 200 300 4000,000 0,0

Temperature (K)

Exponential fitStrongStrong TT-- dependencedependence ofof HHCC

Role of Pt thickness


0,025 10 CoCo9595CrCr55((0.50.5 nm)/Pt(nm)/Pt(z z nm)nm) x 10x 10

Role of Pt thickness

8

H

Co95Cr5 (0.5 nm) / Pt (z nm)

0,020 6

HC

(T)

Sq

ess

(%)

4μ 0H

C(

Squa

rene

0,015 2

S

Cr 5%Cr 5%0,6 0,9 1,2 1,5 1,8 2,1

0

Z Pt (nm)

Th i itTh i it dd th i ith i i Pt thi kth i ith i i Pt thi k


E. Th. Papaioannou et al. Journal of Applied Physics 103, 093905 (2008)

The coercivityThe coercivity andand the squareness increase with increasing Pt thicknessthe squareness increase with increasing Pt thickness

Role of Cr concentration


0.0

Role of Cr concentration

-0.1(deg

)

Cr segregation Cr segregation at the grain at the grain

-0.2

Rot

atio

n (at the grain at the grain

boundaries boundaries

-0.3

olar

Ker

r R Cr = 5 % Cr = 30 %Cr = 30% at 10K

isolated isolated magnetically magnetically

decoupled neighboring decoupled neighboring

1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5-0.4

Po

Cr = 30% at 10K

Co70

Cr30

22 nm thick film

decoupled neighboring decoupled neighboring grainsgrains

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Energy (eV)Kerr rotation ~ MagnetizationDramatic decrease of Kerr rotation with Cr increase


Disappearance of the negative max Kerr rotation peaksSignificant enhancement of the Kerr rotation at short wavelengths for Cr 5 %

Role of Pt polarization


0,06the Pt atoms are strongly polarized

dT=10 K

Role of Pt polarization

0 00

0,02

0,04

L3

and carry magnetic momentsin the vicinity of a FM layer

-0,04

-0,02

0,00

units)

L2

XMCD spectrum0,2

-0,08

-0,06XM

CD

(ar

b. u

PtDirect evidenceof Pt polarization

0,0

0,1

err r

otat

ion

(deg

)

-0,12

-0,10

-10 -5 0 5 10-0,2

-0,1 Ke

H (kOe)

Orbital/Spinmagnetic moment

11,55 11,60 11,65 13,25 13,30 13,35

Energy (keV)

CoCo7070CrCr3030(0.6 nm)/Pt((0.6 nm)/Pt(0.4 0.4 nm)nm) x 30x 30

magnetic moment~ 0.140± 0.01

total magnetic moment carried by Pt


oo7070 3030(0 6 )/ ((0 6 )/ (00 )) 3030y0.17 μB/atom.

Outline


2.Case studies

Multilayers




Nanoparticles



3 O tl k & P ti



Synthesis of CoPt3 nanoparticles

Pt-Co: Finite-size effects

Thermal decomposition of cobalt precursors

Synthesis of CoPt3 nanoparticles

Co2(CO)8 , Co(ac)2.4 H2O, Pt(acac) 2

Reaction temperature: low (135 oC) and high (350 oC)

Solvents trioctylamine

Surfactants ACA (1-adamantanecarboxylic acid) & TOPO (trioctylphosphine-

oxide))

Conditions: inert, open air

Size and yield depends on the precursor and temperature

Diametert d ( )

PrecursorsSolvent-Surfactants

Particle composition (% C )± st.dev. (nm) Solvent Surfactants (% Co)Co Pt Co/Pt ratio

7.1±1.0Co2(CO)8 Pt(acac)2

2:1 TOAm 32

5.4±0.8 1.5:1 TOAm-ACA, TOPO 20


3.1±0.5 Co(ac)2.4H2O 1.5:1 TOAm-ACA, TOPO 26

Structure & Morphology

Pt-Co: Finite-size effectsStructure & Morphology

20

log-normal fitting

Dave=7.07 nmD 5 41

Dave=3.12 nmstdev=0.47 nm

10

15

ave

stdev=1.04 nmDave=5.41 nmstdev=0.79 nm

eque

ncy

(%)

0

5

Fre

2 3 4 5 6 7 8 9 10Mean diameter (nm)

600 CoPt3

)

400

5

7 nm

sity

(arb

. uni

ts200

5 nm in

tens

3 nmmain phase fits to CoPt3

high degree of crystallinity


20 30 40 50 60 70 80 900

2θ (deg)

high degree of crystallinity

Size affects magnetism


20

LN2


2.0

2.5

nits

) 5 nm & 7 nm nanoparticles

10

zatio

n (e

mu/

g)

RT

0 50 100 150 200 250 300-0.5

0.0

0.5

1.0

1.5

Mag

netiz

atio

n (a

rb. u

n

Temperature (K)

100 G

pexhibit ferromagnetic features

even at RT

2

4

LN2

-10

0

Mag

netiz

0

RT

-8 -4 0 4 8-20

4

6

LN2

-4

-2

0

2

RT

-8 -4 0 4 8

-4

-2Suppression of the superparamagnetic size limit under 7 nm, slightly lower than 9 nm reported in CoPt nanostructures


-8 -4 0 4 8-6

Magnetic field (kOe)

9 nm reported in CoPt3 nanostructures by physical vapor methods.



1000

7 nm


600

800

ive

field

(Oe)

200

4005 nm

Coe

rc

100 150 200 250 3000

2003 nm

19

20

ion

(em

u/g) 7 nm

Temperature (K)

4

n M

agne

tizat 3 nm

2Sat

urat

ion

5 nm


100 150 200 250 300Temperature (K)

Outline


2.Case studies

Multilayers




Nanoparticles



3 O tl k & P ti



Pt-Fe: Composition and Structural OrderingSynthesis of ~4 nm Fe Pt1 nanoparticles

Simultaneous thermolytic decomposition or reduction of

organometallic precursors: Fe(CO)5, Pt(acac)2

Synthesis of ~4 nm FexPt1-x nanoparticles

o ga o a p u so s (CO)5, (a a )2

Use of high boiling point organic solvents (e.g. octyl ether, b.p. ~

287 oC), surfactants (e.g. oleic acid, hexadecylamine) and

reducing agents whenever it is needed (e.g. hexadecanediol)

Washing with ethanol or acetone

Dispersion into hexaneDispersion into hexane

Reduction80

% Fe content

Tem size (nm)

XRD size (nm)

PrecursorsFe-Pt ratio

60

prec

urso

r

55 4.8±0.2 4.6±0.3 2.5:1

42 4.2±0.3 3.9±0.1 2.0:1

35 4.0±0.2 3.7±0.2 1.5:1

40% F

e


30 4.1±0.3 4.0±0.2 1.0:1

25 4.4±0.4 4.2±0.1 0.8:1

15 3.8±0.2 4.2±0.3 0.4:1

10 20 30 40 50 6020

% Fe

Pt-Fe: Composition and Structural OrderingPost-synthetic treatmentPost synthetic treatment

Fe: 42%Fe: 42%

800

FePt

ann.as syn.

600

FePtfct

.)

FePtfcc

001 111

200

400(d)

(c)

700oC

nten

sity

(a.u 200

220311

17 nm

200

(c)

(b)

(a)(a)4

6 nm

9 nm550oC

400oC

I

(a)phase transformationphase transformation

h llh ll


20 24 40 50 60 70 80 900

4 nm

2θ

as synthesizedHigher crystallinityHigher crystallinityAgglomerationAgglomeration

Pt-Fe: Composition and Structural OrderingAnnealing conditions

60

30 min

Annealing conditions

Fe: 42%Fe: 42%

20

40

n (e

mu/

g)

30 min 60 min 90 min

Optimum annealing conditionsOptimum annealing conditions90 min in Ar/H90 min in Ar/H22

-20

0

Mag

netiz

atio

80

90 min in Ar/H90 min in Ar/H22

-1.0 -0.5 0.0 0.5 1.0-60

-40

M annealed 700oC Ar

40

60

emu/

g)

Ar/H2

Ar as prepared

Magnetic field (T)

0

20

netiz

atio

n (e

CriteriaCriteria

-60

-40

-20M

agn

annealed 700oC 90'

XRD: lack of oxidationXRD: lack of oxidationVSM: Magnetic hardening VSM: Magnetic hardening

TEM: Limited agglomerationTEM: Limited agglomeration


-1.0 -0.5 0.0 0.5 1.0

Magnetic field (T)

Pt-Fe: Composition and Structural OrderingComposition dependent hardening

Composition dependent hardening

FePtFePt as prepared annealed

20

40

60

atio

n (e

mu/

g)

as prepared annealed

FePtFePt

42% Fe700oC 90'Ar/H

-40

-20

0 M

agne

tiza

55% Fe700oC 90'Ar/H

as prepared60

as prepared

as prepared

-1.0 -0.5 0.0 0.5 1.0

Ar/H2

Magnetic field (T)-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

-60

Magnetic field (T)

Ar/H2FePtFePt33


0

20

40

atio

n (e

mu/

g)



25% Fe 700oC 90'Ar/H

2-60

-40

-20

Mag

netiz

35% Fe700oC 90'Ar/H2

30% Fe700oC 90'Ar/H2


-1.0 -0.5 0.0 0.5 1.0

Magnetic field (T)-1.0 -0.5 0.0 0.5 1.0

Magnetic field (T)-1.0 -0.5 0.0 0.5 1.0

Magnetic field (T)

Pt-Fe: Composition and Structural OrderingComposition dependence orderingComposition dependence ordering

FePtFePtFePtFePt33

2) 2

rciv

ity (k

Oe)

FePtFePtFePtFePt331

Coe

r

60

10 20 30 40 50 600

% Fe

40

Mr/M

s (%)

20


10 20 30 40 50 600

% Fe

Outline


2.Case studies

Multilayers




Nanoparticles



3 O tl k & P ti



Outlook & PerspectivesMultilayersMultilayers

Pt-SmCo: Multilayer modulation vs thin filmThe use of multiple Pt interlayer serving as dedicated buffer layers seems to

promote crystallization of SmCo phase as evidenced by structural features and enhanced magnetic behavior.

M. Angelakeris et al. Accepted for publication in JMMM 2008.

Pt-Co: Interface Effects at the Monolayer LimitTh d l i f C l i h P l f i hi k The modulation of one or two Co monolayers with Pt layers of varying thickness

significantly affects macroscopic magnetic behavior and allows for the enhancement of magnetic features of technological interest.

M. Angelakeris et al. Phys. stat. sol. (a), 1– 5 (2008).

Pt-CoCr: Adjustable perpendicular anisotropyPerpendicular magnetic anisotropy with square loops has been achieved for both Perpendicular magnetic anisotropy with square loops has been achieved for both

Cr 30% & 5. Enhancement of the magneto-optic Kerr effect due to the highly polarized Pt.

E Th Papaioannou et al Journal of Nanoscience & Nanotechnology 7 1 (2007)


E. Th. Papaioannou et al. Journal of Nanoscience & Nanotechnology 7,1, (2007).

E. Th. Papaioannou et al. Journal of Applied Physics 103, 093905 (2008).

Outlook & PerspectivesNanoparticlesNanoparticles

Pt-Co: Finite size effects

The appearance of stable magnetic properties and the high degree of crystallinityat such low sizes promotes the fixing of the desirable magnetic propertiesat such low sizes promotes the fixing of the desirable magnetic propertiesduring synthesis against post-annealing treatment.

S. Mourdikoudis et al. submitted to Journal of Nanoscience & Nanotecholohy 2008

Pt-Fe: Composition and Structural Ordering

Depending on composition post deposition treatment promotes different degreeDepending on composition post deposition treatment promotes different degreeof structural ordering and stronger ferromagnetic behavior.

F. Wilhelm et al. Mod. Phys. Let. B 21, 1189 (2007).

K Simeonidis et al J Magn Magn Mater 320 2665– 2671 (2008)K. Simeonidis et al. J. Magn. Magn. Mater. 320 2665 2671 (2008).

M. Angelakeris et al. Journal of Nanoscience & Nanotechnology submitted (2008).


Acknowledgements

Nanoparticles Physics Department-AUTh

MultilayersPhysics Department-AUTh Physics Department AUTh

A. Vilalta-Clemente-K. GloysteinK. Simeonidis-S. MourdikoudisI. Tsiaoussis-O. Kalogirou

Physics Department AUThI. Tsiaoussis-N.K. Flevaris

Materials Science-Univ. of PatrasP Poulopoulos

Chemistry Department-AUThC. Dendrinou-Samara

XMCD

P. Poulopoulos

Materials Physics-Univ. of Uppsala V. Papaioannou

XMCDA. Rogalev- F. Wilhelm

ID12, ESRF

Freie Univ.-BerlinP. Fumagalli

,

Greek Secretariat of Research and Technology(PENED 03Δ667)

Synthesis and Orbital Magnetism on core-shell nanoparticles (MRTN-CT-2004-0055667)

8th International Workshop on Synthesis and Orbital Magnetism of core-shell nanoparticles Mittelwihr, October 24-25, 2008 44http://multigr.physics.auth.gr/multigrhttp://multigr.physics.auth.gr/multigr

Network of Laboratories on Growth and Characterization of Magnetic Materials (web.auth.gr/mag-net)

The effect of intentional alloying The effect of intentional alloying in the magnetism

of XPt (X Fe Co) Based Nanostructuresof XPt (X=Fe, Co) Based Nanostructures

M. AngelakerisDepartment of PhysicsDepartment of Physics

Aristotle Universityof Thessaloniki

The 8th International Workshop


on Synthesis and Orbital Magnetism of core-shell nanoparticles

Mittelwihr, October 24-25, 2008

the effect of intentional alloying in the magnetism of xpt (x fe...

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