Detection of irreversible fusion of iron oxide magnetic nanoparticles into single-domain

clusters by magnetic measurements

M Jagodič, S Gyergyek,Z Jagličić, D Makovec, Z Trontelj

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

Introduction

• aggregation behavior of a ferrofluid technical andmedical applications

• method for determining the extent of aggregation!

• aggregates (many particles) & clusters (few particles)

• physical properties change: magnetic properties

• bigger clusters stronger interactions aggregates

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

Introduction

The aim of our work:

• the potential use of magnetic measurements for determining the extent of particle fusion

Which is the most evident magnetic measurement method for detecting the fusion of particles?

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

Ferrofluid structure and measuring procedure

• γ-Fe2O3 particles coated with oleic acid and dispersed in n-decane:

• concentrated (45.6 wt%) – strong interactions• diluted (2.6 wt%) – no (or low) interactions

• ZFC/FC susceptibility, M(H), AC susceptibility on zero field-frozen and field-frozen samples

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

Results: TEM

• as-prepared ferrofluid: 10.6 ± 2.9 nm

• zero field-dried and field-dried ferrofluid clustering and aggregate formation

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

Results: ZFC/FC susceptibility

• superparamagnetic behavior

• concentrated samples: constant FC curves below Tpeak considerable inter-particle interactions

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

0 30 60 90 120 150 180 210

0.0

0.1

0.2

0.3

0.4

0.5

diluted-ZFF diluted-FF concentrated-ZFF concentrated-FF

(a)

[e

mu

/g]

T [K]

Results: ZFC/FC susceptibility

• diluted samples: Tpeak is not affected by the freezing procedure no fusion of particles

• concentrated samples: Tpeak shifts to lower T if the sample is field-frozen!?

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

80 100 120 140 160 180 200

0.20

0.25

0.30

0.35

0.40

0.45 Tpeak

[e

mu

/g]

T [K]

(b)

0 30 60 90 120 150 180 210

0.0

0.1

0.2

0.3

0.4

0.5

diluted-ZFF diluted-FF concentrated-ZFF concentrated-FF

(a)

[e

mu

/g]

T [K]

Results: M(H) measurements

• average particle diameter obtained from Langevin fit:

~50% increase in V

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

Results: AC susceptibility

• diluted samples: Arrhenius law

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

60 80 100 120 140 160 180 200 220 2400.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

1 Hz 10 Hz 100 Hz 1000 Hz

' [e

mu

/g]

T [K]

TB

4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2-8

-6

-4

-2

0

diluted-ZFF diluted-FF Arrhenius law

ln(

-1)

1/TB [kK-1]

0 exp( )a

B

E

k T

Results: AC susceptibility

• concentrated samples: Vogel-Fulcher law

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007

200 205 210 215 220 225 230 235 240

0.0

0.2

0.4

0.6

0.8

1.0 concentrated-ZFF concentrated-FF Vogel-Fulcher law

-1 [

s]

TB [K]

00

exp( )

a

B

E

k T T

~65% increase in V

Conclusions

diluted samples: • ZFC/ZF, M(H), AC: no particle fusion

concentrated samples:• M(H), AC: increase in average particle size• ZFC/FC: no relevant information

SLONANO2007, Ljubljana, Slovenia, 10–12 October 2007