Self-assembling magnetic nano-Self-assembling magnetic nano-particles for advanced applications particles for advanced applications

Ovidiu CrisanOvidiu Crisana,a,, J. M. Grenéche, J. M. Grenéchecc, , M. AngelakerisM. Angelakerisbb and and George Filoti aa

aa National Institute for Materials Physics, Bucharest, Romania National Institute for Materials Physics, Bucharest, Romaniabb LPEC-CNRS UMR 6087, Université du Maine, Le Mans, France LPEC-CNRS UMR 6087, Université du Maine, Le Mans, Francec c Aristotle University, Dept. of Physics, Thessaloniki, GreeceAristotle University, Dept. of Physics, Thessaloniki, Greece

Special Special

Nano-particlesNano-particles NP’s may be obtained in NP’s may be obtained in 2D regular arrays or 3D 2D regular arrays or 3D super-lattices by super-lattices by self-self-assemblyassembly

Breakthrough in data Breakthrough in data storage, biomedicine, storage, biomedicine, catalysis, nano-electronicscatalysis, nano-electronics

Anomalous magnetic behavior driven by Anomalous magnetic behavior driven by finite size finite size effectseffects and / or and / or surface spin disordersurface spin disorder

Nanometer scale confinement give rise to possible Nanometer scale confinement give rise to possible non-crystallographicnon-crystallographic symmetries for NP’s symmetries for NP’s

SynthesisSynthesis

Decomposition of metallic precursors Decomposition of metallic precursors followed by transmetalation reactionfollowed by transmetalation reaction

Wet (colloidal) chemistry technique and Wet (colloidal) chemistry technique and coating with organic surfactantscoating with organic surfactants

AgAg5555CoCo

4545 and and AgAg3030CoCo

7070 bimetallic nano- bimetallic nano-

particles dispersed in tolueneparticles dispersed in toluene

Co2(CO)8+AgClO4 Ag+Co+CO+Co(ClO4)2

Basic of self assembling n-Basic of self assembling n-particlesparticles

Allowed engineering of Allowed engineering of regular arrays of nano-regular arrays of nano-entitiesentities onto very large sample areas onto very large sample areas

Extremely sensitive GMR and SDT effects exhibited by Extremely sensitive GMR and SDT effects exhibited by these nano-particles provide a these nano-particles provide a detection with very high detection with very high spatial resolutionspatial resolution

Using a suitable substrate for magnetic nano-Using a suitable substrate for magnetic nano-arrays both the arrays both the signal conditioning and the signal conditioning and the logistic capabilitylogistic capability can be used to optimize the can be used to optimize the system performancesystem performance

SSeellff--aasssseemmbbllyy iiss aa vveerryy rreelliiaabbllee aanndd aattttrraaccttiivveessyynntthheessiiss tteecchhnniiqquuee ffoorr nnaannoo--ssttrruuccttuurreess ::

Nanoparticles MorphologyNanoparticles MorphologySEM:SEM: Ag Ag

3030CoCo7070 dried on Si(100) substrate dried on Si(100) substrate

under applied field Hunder applied field H

H

Formation of straight stripes of Formation of straight stripes of ~20 ~20 m m length oriented along the applied field Hlength oriented along the applied field H

Nanoparticles MorphologyNanoparticles MorphologySEM:SEM: Ag Ag

3030CoCo7070 dried on Si(100) substrate dried on Si(100) substrate

under rotating applied field Hunder rotating applied field H

H Formation of Formation of winding stripes and winding stripes and round shapes whenround shapes when the applied field the applied field HH rotates in the sample rotates in the sample planeplane

Nanoparticles MorphologyNanoparticles Morphology

Columnar growth of Columnar growth of uniformly dispersed NP’suniformly dispersed NP’s

Growth modes strongly Growth modes strongly dependent on the substrate dependent on the substrate naturenature

AFM:AFM: Ag Ag3030CoCo7070 on: on:

a) a) Si(100) Si(100) wafer wafer

b)b) Co/Pt Co/Pt multilayer deposited on Simultilayer deposited on Si

c)c) 80 nm Pd 80 nm Pd thin film on kaptonthin film on kapton

d)d) 100 nm Pt 100 nm Pt on Si patterned substrate.on Si patterned substrate.

AFM:AFM: Ag Ag3030CoCo7070 on on 7nm Pt / 200nm 7nm Pt / 200nm

PMMA / SiPMMA / Si patterned substrate patterned substrate

substrate choicesubstrate choiceprevention of clustering prevention of clustering during during self-assemblyself-assembly

Patterning as factor of Patterning as factor of controlling 2D arrayscontrolling 2D arrays

NanoparticlesNanoparticles structure structureTEM images ofTEM images of Ag Ag

3030CoCo7070 nanoparticles nanoparticles

Mean size: Mean size: d = 18nmd = 18nm Distribution Distribution width: width: 12%12%

Relatively dispersedRelatively dispersed Narrow log-normal size Narrow log-normal size distributiondistribution

Multiphase (polycrystalline) Multiphase (polycrystalline) nano-grainsnano-grains

Bimetallic character with a Bimetallic character with a (incomplete) core-shell structure(incomplete) core-shell structure

NanoparticlesNanoparticles structure structureHigh resolution TEM images ofHigh resolution TEM images of AgCo AgCo nanoparticles nanoparticles

Single-crystalline Single-crystalline hcp Co particlehcp Co particle

Ag core and Co as Ag core and Co as incomplete shellincomplete shell

Both Both icosahedral icosahedral (from MTP) and (from MTP) and fccfcc symmetry co-exist for Ag symmetry co-exist for Ag

Ag core with (111) Ag core with (111) twin and Co twin and Co patches as shellpatches as shell

Single-crystalline Single-crystalline five-fold twinned Ag five-fold twinned Ag particle particle

Co shells and Co single particles Co shells and Co single particles show show fccfcc and and//or or hcphcp symmetry symmetry

NanoparticlesNanoparticles structure structureXRD ofXRD of Ag Ag

3030CoCo7070 on on Si(100)Si(100)

Multiphase symmetry for Co (Multiphase symmetry for Co (fcc fcc and/or and/or hcphcp)) and and for Ag (for Ag (icosahedralicosahedral and and fccfcc))

Evidence of Evidence of layeringlayering nanoparticles from small angle XRD nanoparticles from small angle XRD Periodical 3D superlattice: Periodical 3D superlattice: 4.5 nm4.5 nm

Line profile from EDP ofLine profile from EDP of Ag Ag3030CoCo

7070

10 20 30 40 50 60 70 80 90

2

hcp

Co

(1

10

)

hcp

Co

(1

01

)h

cp

Co

(0

02

)

fcc C

o (

20

0)

fcc C

o (

11

1)

fcc A

g (

31

1)

fcc A

g (

22

0)

fcc A

g (

20

0) f

cc A

g (

11

1)

Inte

nsity (

a.u

.)

Need of a quantitative model to account for multiple Need of a quantitative model to account for multiple symmetries ?symmetries ?

Magnetism of Magnetism of AgAg3030CoCo

7070NanoparticlesNanoparticles

-0.2 -0.1 0.0 0.1 0.2

-0.2

0.0

0.2

-6 -4 -2 0 2 4 6

-1

0

1

M (

emu/

g)

H (T)

HC = 145 Oe

Mr = 0.048 emu/g

M (

emu/

g)

H (T)

0 1 2 3 4 5 6

0

2

4

6

8

10

12 Ag30

Co70

M (

emu/

g)

H (T)

4.5K 10K 25K 50K 75K 293K Langevin fit

Lack of saturation even at 5.5 TLack of saturation even at 5.5 T

Small hysteresis at RTSmall hysteresis at RT

MM influenced by influenced by surface spin surface spin disorder disorder and/orand/or finite size finite size effectseffects Shape of Shape of M(H)M(H) indicates indicates two-phase behaviortwo-phase behavior

M(H)M(H) follows follows a a Langevin lawLangevin law::

kT

HLMHM s

Co-existence of interacting Co-existence of interacting SPMSPM NP’s and NP’s and ferromagneticferromagnetic clusters clusters

Monte Carlo study of nMonte Carlo study of nanoparticlesanoparticles magnetic propertiesmagnetic properties

Isolated ferromagnetic nanoparticle Isolated ferromagnetic nanoparticle R = 6R = 6aa (905 atoms)(905 atoms) and R = 15 and R = 15a a (14137 atoms)(14137 atoms) Heisenberg-type hamiltonian:Heisenberg-type hamiltonian:

iextBSiSViVVj

jiiji SHgnSKySKSSJH

2

,

2

, ˆˆ

Periodic boundary conditionsPeriodic boundary conditions

SSi,ji,j = 1; J = 1; Jijij = 1000; K = 1000; KVV = 20; K = 20; Kss = 0.2 = 0.2 2000; 2000;

KKVV – uniaxial; K – uniaxial; Kss – normal to the surface – normal to the surface

101055 Monte Carlo steps / spin / temperature Monte Carlo steps / spin / temperature

Spin configuration energy is minimized using a Spin configuration energy is minimized using a Metropolis algorithmMetropolis algorithm

MCS simulationsMCS simulations

R = 15a, Ks/KV = 10:

throttled spin configurationthrottled spin configuration Surface magnetization Surface magnetization reversal at equatorreversal at equator

R = 15a, Ks/KV = 60:

throttled spin configurationthrottled spin configuration Vortex-type reversal Vortex-type reversal centers migrate towards centers migrate towards lower hemisphere lower hemisphere

MCS simulationsMCS simulations

R = 15a: M(T) for different Ks

M M as K as Kss : reduced : reduced

magnetization due tomagnetization due to surface spin disordersurface spin disorder M(TM(TCC) ) 0 features 0 features

finite size effectsfinite size effects Instabilities in the Instabilities in the transition regiontransition region Sharp decrease of Sharp decrease of magnetization in the magnetization in the transition regiontransition region Overall magnetization Overall magnetization strongly influenced strongly influenced by the surface spin by the surface spin configurationconfiguration

MCS simulationsMCS simulations

R = 6a, Ks/KV = 1 collinear

R = 6a, Ks/KV = 10 throttled

R = 6a,

Ks/KV = 40throttled (reversalcenters)

R = 6a,

Ks/KV = 60hedgehog (M=0)

MCS simulationsMCS simulations

R = 6a : M(T) for different Ks

M M as K as Kss :: surface surface spin disorderspin disorder IncreasedIncreased finite size finite size effects effects compared to compared to R = 15R = 15aa Ks/KV = 10 20:

Transition from Transition from collinear to throttled collinear to throttled spin configurationspin configuration

Ks/KV = 50:

Transition from Transition from throttled to hedgehog throttled to hedgehog spin configuration spin configuration (M=0)(M=0)

Conclusions - PerspectivesConclusions - PerspectivesAgAg

3030CoCo70 70 bimetallic nanoparticles:bimetallic nanoparticles:

Exhibit Exhibit different growth modesdifferent growth modes depending on depending on substrates nature and depositing parameters substrates nature and depositing parameters

Self-assembly Self-assembly of NP’s onto large 2D arrays imposed of NP’s onto large 2D arrays imposed themselves for technological applicationsthemselves for technological applications Exhibit Exhibit anomalous magnetic behavioranomalous magnetic behavior driven by the driven by the multiphase multiphase character of the sample, character of the sample, finite size effectsfinite size effects and and surface spin disordersurface spin disorder

Their ‘in situ’ as well as self-organized on substrates Their ‘in situ’ as well as self-organized on substrates phase compositionphase composition, , magneticmagnetic and and magneto-transportmagneto-transport properties needs further investigations properties needs further investigations inin order to order to promote performing functional materialspromote performing functional materials

The PROJECT aims:The PROJECT aims:(on self-assembling(on self-assembling nano-particles)nano-particles)

to develop to develop a new generation of magnetic sensorsa new generation of magnetic sensors

to process to process the self-organization of colloidal nano-the self-organization of colloidal nano-particles on a single chip of regular 2D array of particles on a single chip of regular 2D array of magnetic sensorsmagnetic sensors

to optimizeto optimize systems able to detect very small systems able to detect very small magnetic fields with very high spatial resolutionmagnetic fields with very high spatial resolution

to allow to allow mutual sharing of each partner facilities for mutual sharing of each partner facilities for deeper and faster research, promoting earlier results at deeper and faster research, promoting earlier results at level of functional materialslevel of functional materials

to promote to promote an improved level of each partner an improved level of each partner professional abilities by reciprocal training professional abilities by reciprocal training

The PROJECT goals:The PROJECT goals:(on new self-assembling(on new self-assembling nano-particles)nano-particles) to select to select new new element-pairselement-pairs for high performing for high performing magnetic sensorsmagnetic sensors

to use alternative procedures to use alternative procedures in order to obtainin order to obtain the the best self-organizationbest self-organization of colloidal nano-particles on a of colloidal nano-particles on a single chip of magnetic sensorssingle chip of magnetic sensors

to define to define the the most suitable supportmost suitable support which provides the which provides the highest spatial resolution highest spatial resolution

to search to search for a for a competitively low cost technologycompetitively low cost technology for for very efficient very efficient bank-notes and credit cardbank-notes and credit card survey / check survey / check via complex functional devicesvia complex functional devices

ESTABLISHED:ESTABLISHED: National Institute for Materials Physics, BucharestNational Institute for Materials Physics, BucharestLPEC-CNRS UMR 6087, Université du Maine, Le LPEC-CNRS UMR 6087, Université du Maine, Le Mans, Mans, Aristotle University, Dept. of Physics, Thessaloniki, Aristotle University, Dept. of Physics, Thessaloniki,

POTENTIALLY……...POTENTIALLY……... Science ofScience of MaterialsMaterials Institute, ZaragozaInstitute, Zaragoza University of Padova, Metal-organic ChemistryUniversity of Padova, Metal-organic Chemistry Institutul de Chimie, ChisinauInstitutul de Chimie, Chisinau

ICPE- CA and IMT, both in BucharestICPE- CA and IMT, both in Bucharest ICF-Bucharest + ICM- Iassy (both Romanian Academy)ICF-Bucharest + ICM- Iassy (both Romanian Academy) CN-IS-FC- University of Timisoara CN-IS-FC- University of Timisoara MAVILOR-motors, Barcelona and Pro-Auto MAVILOR-motors, Barcelona and Pro-Auto - Bucharest (both are SME) - Bucharest (both are SME)

PARTNERSPARTNERS