Influence of an applied magnetic field on the magnetic nanoparticles assembly

P. Jenuš1,2, D. Lisjak1, A. Mertelj3, D. Križaj4, D. Kovačič5, D.

Makovec1

1Jožef Stefan Institute, Department for Materials Synthesis, Ljubljana, Slovenia. 2Jožef Stefan International Postgraduate School, Ljubljana, Slovenia.

3Jožef Stefan Institute, Complex Matter Department, Ljubljana, Slovenia. 4University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia.

5 LPKF Laser & Elektronika d.o.o, Naklo, Slovenia.

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[email protected]

NanoAPP 2013

The particles rearrange themselves during the solvents evaporation;

Magnetic dipole-dipole interactions

=> important; * � = � ��

* < >= � +4�−+ �− +4� , �ℎ��� � = �� �

Technical simplicity and low

production costs.

The effect of the applied field

mi mj

rij H = 0 and

Em < kT

mi mj

rij H > 0 or

Em > kT

Increasing H

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* Rosensweig, R. E. Ferrohydrodynamics; Cambridge University Press, New York, USA, 1985.

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Cobalt ferrite (CoF)

Hydrothermal synthesis (HT)*

Aqueous solutions of Fe3+ and Co2+ ions (molar ratio 2:1)

Sodium hydroxide (NaOH, C=1,6 mol/L)

120°C, 5, 10, 30 or 120 min; 200°C, 120 min

CoF nanoparticles

Maghemite (MN)

Co-precipitation method - two-step process **

Aqueous solutions of Fe3+ and Fe2+ ions (molar ratio 2:1)

Concentrated ammonia solution

(NH3 (aq), 25 %)

Room temperature

MN nanoparticles

* Gyergyek et al., Mater. Chem. Phys., 133, 2012, 515-522; ** Campelj et al. , J. Phys.: Condens. Matter, 20, 2008, 204101 (5pp)

Adsorption of citric acid (CA)

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sample synthesis

conditions d (nm) Ms (Am2/kg)

suspension

concentration

(g/L)

-potential

(mV)

CoF1 120°C, 5 min 6 ( 2) 26 10 -63

CoF2 120°C, 10 min 8 ( 3) 42 10 -66

CoF3 120°C, 30 min 10( 2) 51 10 -62

CoF4 120°C, 120 min 12( 3) 59 10 -68

CoF5-1 200°C, 120 min 20( 4) 68 10 -49

CoF5-2 200°C, 120 min 20( 4) 68 20 -43

CoF5-3 200°C, 120 min 20( 4) 68 30 -45

MN co-precipitation 14( 3) 70 10 -40

CoF 5

CoF 1

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Without Fe template,

0.03 T, 0.5 T

With Fe template

0.5 T In-situ study with

optical microscopy

electromagnet

holder

camera

Homogeneous magnetic field: 0-0.08 T

Stable suspensions

CoF – 6 nm, Ms = 26 emu/g

CoF – 20 nm, Ms = 68 emu/g

MN – 14 nm, Ms = 70 emu/g

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CoF nanoparticles

d 20 nm

Ms = 68 emu/g

sample d (nm) concentration

(g/L)

Ms

(emu/g)

m (B=0.03

T)

<n>

(B=0.03 T)

CoF5-1 20 10 68 11 33103

CoF5-2 20 20 68 11 37103

CoF5-3 20 30 68 11 45103

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sample d (nm) concentration

(g/L) Ms (Am2/kg) m (B=0.5 T)

<n> (B=0.5T)

CoF1 6 ( 2) 10 26 2 5

CoF4 12( 3) 10 59 34 41014

CoF5-3 20( 4) 30 68 183 3.51079

MN 14( 3) 10 70 65 71027

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CoF nanoparticles

d 20 nm

Ms = 68 emu/g

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Co-ferrite and maghemite nanoparticles were assembled under applied magnetic fields with different strengths and set-ups.

Under an applied field of 0.03 T particles assembled into flat films. When the strength of the applied field is higher (0.5T) the larger, 20-

nm-sized Co-ferrite and maghemite nanoparticles assembled into columnar structures.

Soft-Fe template in a combination with the applied field of 0.5 T

guided nanoparticles to assemble into structures with template defined morphology.

Columnar Co-ferrite structures are displaying promising (magnetic)

properties and can be further used for the preparation of magneto-electric composites with 1-3 structure.

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This work was financially supported by the Slovenian

Research Agency.

The CENN Nanocenter for the use of TEM equipment.

Co-workers from Department for Materials Synthesis.