FORMATION AND CHARACTERISATION OF FORMATION AND - - PowerPoint PPT Presentation

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FORMATION AND CHARACTERISATION OF FORMATION AND CHARACTERISATION OF NANOSTRUCTURED METASTABLE ALLOYS NANOSTRUCTURED METASTABLE ALLOYS

Viorel Pop Faculty of Physics, Babes-Bolyai University, 3400 Cluj-Napoca, Romania

Nanocrystalline materials obtained by:

• vapour - inert gas condensation, sputtering, plasma processing, vapour

deposition

• liquid - electrodeposition, rapid solidification
• solid - mechanical alloying, severe plastic deformation, spark erosion

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mechanical alloying

and

rapid quenching nanostructured hard

and

soft magnetic materials

ANNEALING modifies

the structure and microstructure

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∉ Thermodynamic

equilibrium conditions mechanical alloying

and

rapid quenching Metastable phases

F

Metastable Stable Instable Energy barrier

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Generally, there are three empirical requirements which must be satisfied by magnetic alloys to produce amorphous precursor

Nanocrystalline structures can be obtained directly amorphous precursors

• 1. The alloys are composed of more than three elements.
• 2. The constituent alloying elements have significantly

different atom size.

• 3. The heat formation of the amorphous alloys is negative.

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exchange-spring magnets Hard phase exchange Soft phase high anisotropy large magnetisation

+

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h

cr D δ 2 ≈

h h h

K A / π δ =

Dcr = soft phase critical dimension δh = width of domain wall in the hard phase Ah and Kh are the exchange and anisotropy constants

exchange-spring magnets Hard phase exchange Soft phase high anisotropy large magnetisation

+

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EXPERIMENTAL criteria for the presence of the exchange spring mechanism Large reversible demagnetization curve A strength remanence mr > 0.5 (mr = Mr/Ms)

+

}

In hard magnetic nanocrystalline materials full or almost full crystallization is required.

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Nanocrystalline soft magnetic materials partial crystallisation two-phase materials a nanocrystalline an amorphous matrix

+

}

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Nanocrystalline soft magnetic materials partial crystallisation two-phase materials a nanocrystalline an amorphous matrix

+

}

negative magnetostriction positive magnetostriction compensates

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Nanocrystalline soft magnetic materials partial crystallisation two-phase materials a nanocrystalline an amorphous matrix

+

}

negative magnetostriction positive magnetostriction compensates Vcr ≈70-75 % for Fe

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Nanocrystalline soft magnetic materials partial crystallisation two-phase materials a nanocrystalline an amorphous matrix

+

}

negative magnetostriction positive magnetostriction compensates

D = nanocrystallite diameter Lex = magnetic exchange length

Vcr ≈70-75 % for Fe D < Lex;

2

4 /

s ex

M A L π =

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Nanocrystalline soft magnetic materials partial crystallisation two-phase materials a nanocrystalline an amorphous matrix

+

}

negative magnetostriction positive magnetostriction compensates

D = nanocrystallite diameter Lex = magnetic exchange length

Vcr ≈70-75 % for Fe D < Lex;

2

4 /

s ex

M A L π = D<15 nm for a-Fe(Si) and a-Fe nanocrystals present in Finemet (Fe73.5Cu1Nb3Si13.5B9) and respectively Nanoperm (Fe84Zr3.5Nb3.5B8Cu1)

• G. Herzer, IEEE Trans. Magn. MAG-25 (1989)

3327; IEEE Trans. Magn. MAG-26 (1990) 1397

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Grain size, D(nm) 10 100 1000

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vanish of the coercivity in superparamagnetic regime low permeability soft magnetic nanostructures low coercivity and high permeability small ferromagnetic crystallites coupled by exchange interactions The local anisotropies are randomly averaged out by exchange interactions so that there is no anisotropy net effect on the magnetisation process.

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Nanocrystalline structure is obtained 2 steps:

• 1. Formation of the amorphous state by rapid

quenching of liquid alloy at very high cooling rate of 105-106 K/s.

• 2. Partial or complete crystallisation of the

amorphous alloy by annealing. Rapid quenching

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Nanocrystalline structure is obtained 2 steps:

• 1. Formation of the amorphous state by rapid

quenching of liquid alloy at very high cooling rate of 105-106 K/s.

• 2. Partial or complete crystallisation of the

amorphous alloy by annealing. Rapid quenching Spin melting

Argon r.f. Coil Crucible Melt Copper roller Melt-spun ribbon

vr vr = 20 -30 m/s vr = 80 m/s !!!

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*λs−saturation magnetostriction constant

**

−averaged magnetocrystalline anisotropy

• T. Kulik, J. Non Crystalin Solids 287 (2001) 145

High coercivity, high remanence High permeability, low magnetic losses Properties < 25 nm

≤ 15 nm ⇒ ≈ 0**

D ≤ 100 % 70−75 % ⇒ λs ≈ 0* Vcr Nanocrystals Nd2F14B+ (Fe3B, a-Fe, amorphous) Nanocrystals (bcc-Fe)+ amorphous matrix Structure R-Fe-B R = rare-earth e.g. Nd11.8Fe82.3B5.9 Pr5Fe88Nb2B5 Finemet (Fe73.5Cu1Nb3Si13.5B9) Nanoperm (Fe84Zr3.5Nb3.5B8Cu1) Hitperm (Fe44Co44Zr7B4Cu1) Alloys Magnetically hard (Fe-based) Magnetically soft (Fe-based) Nanocrystalline materials Table 1. General characteristics of the soft and hard magnetic materials produced by annealing of metallic glasses. K K

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Schematic illustration of the formation of the nanocrystalline structure in Fe-Cu-Nb-Si-B alloys based on atom probe analysis results and TEM

• G. Herzer, Handbook of Mag. Mater., Ed. K.H.J. Buschow, Vol 10 (1997) 415

Spin melting SOFT Nb

Promote the formation

• f Cu-rich clusters

Increase the density of Fe nucleation in between Cu-clusters Inhibits the formation

• f Fe boride compounds

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Annealed 1h/540 °C

• G. Herzer, Handbook of Mag. Mater., Ed. K.H.J. Buschow, Vol 10 (1997) 415

Spin melting SOFT

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Annealed 1h/540 °C

• G. Herzer, Handbook of Mag. Mater., Ed. K.H.J. Buschow, Vol 10 (1997) 415

Spin melting SOFT

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• G. C. Hadjipanayis, J. Magn. Magn. Mater. 200 (1999) 373.

DTA – differential thermal analysis

• O. Crisan et al., ICM Rome 2003

DSC – differential scanning calorimetry

Fe73.5Cu1Nb3Si13.5B9 Fe68.5Gd5Cu1Nb3Si13.5B9 R6Fe87Nb1B6

Spin melting SOFT

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Spin melting hard

Kronmuller & Coey Magnetic Materials, in European White book

• n Fundamentel Research

in Materials Science Max Planck Inst. Metallforschung, Stuttgart, 2001, 92-96

(BH)max = 1090 kJ/m3 for Sm2Fe17N3/Fe65Co35 nanostructured multilayers

• R. Skomski, J. Appl. Phys. 76 (1994) 7059

melt spinning

• r

mechanical alloying Nd2Fe14B/(Fe3B, Fe)

and

Sm2Fe17N3/Fe by high magnetisation of soft phases - Fe, Fe3B…

+

high magnetic anisotropy of R compounds - Nd2Fe14B, Sm2Fe17N3…

Spin melting HARD

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• H. A. Davies, J. Magn. Magn. Mater. 157-158 (1996) 11

Behaviour connected to the microstructure changes in the melt spun evidenced by, TEM Spin melting hard Spin melting HARD

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• X. Y. Zhang, J. W. Zhang, W. K. Wang, J. Appl. Phys. 89 (2001) 477

Annealing 923 K

p normal 6 GPa Spin melting hard Spin melting HARD

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The volume fraction of Sm2(Fe,Si)17Cx phase also increases as the pressure increases. This behaviour is explained by the change of the crystallisation sequence: at low pressure a-Fe is the first crystallisation phase, while at high pressure Sm2(Fe,Si)17Cx is.

• X. Y. Zhang, J. W. Zhang, W. K. Wang, J. Appl. Phys. 89 (2001) 477

Annealing 923 K

p normal 6 GPa Spin melting HARD

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• X. Y. Zhang, J. W. Zhang, W. K. Wang, J. Appl. Phys. 89 (2001) 477

Spin melting HARD

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Mechanical alloying D - ductile component B - brittle component C - composite (compound) D1 D2 D1 B1 B1 B2 C1 C2 C3

Mechanical alloying involves the synthesis of materials by high-energy milling Mechanical milling refers to the process of milling pure metals or compounds which are in thermodynamical equilibrium before milling

MA MM

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• milling of Ni and Fe powders in a high energy planetary mill
• heat treatments (temperatures and duration)
• X-rays diffraction (XRD)
• electron microscopy

morphology phase composition checked by EDX

• magnetic measurements: 4 - 600 K; µ0H ≤ 8 T
• Mössbauer spectrometry

Mechanical alloying Ni3Fe

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The presence of the first order internal stresses acts at a macroscopic level and modifies the lattice parameters and consequently produces an angular shift of the X-ray diffraction peaks. The second-order internal stresses act at a microscopic level of the crystallites and produce a broadening of the X-ray diffraction peaks [13, 16].

• L. Castex, J.L. Lebrun, G. Maeder, J.M. Sprauel, Determination de contraintes

résiduelles par diffraction des rayons X, Publications scientifiques et techniques de l’ENSAM, Paris vol.22 (1981), 51-60. See also http://WWW.physiqueindustrie.com/

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ss 1h 1h+330°C/1h 2h 2h+ 330°C/1h 3h 3h+330°C/1h 4h 4h+330°C/1h 6h 6h+330°C/1h 8h 8h+330°C/1h 10h 10h+330°C/1h 12h 12h+330°C/1h

Intensité (unit. arb.) 2 theta (degrés)

3 6 40 50 6 7 8 9

40 50 60 70 80 90

Intensité (u.a.) 2 t h e t a

8 9 . 2 9 0 9 1 9 2 9 3 9 4 9 5

Ni3Fe Ni

1h 1h+ 330°C/1h 2h 2h+ 330°C/1h 3h 3h+ 330°C/1h 4h 4h+ 330°C/1h 6h 6h+ 330°C/1h 8h 8h+ 330°C/1h 10h 10h+ 330°C/1h 12h 12h+ 330°C/1h ss

90 91 92 93 94 95

2 θ (°) 2 θ (°)

Intensity (a.u.) Intensity (a.u.)

Fe Fe Ni3Fe Ni

peaks shift to lower 2θ angles peaks shift to HIGHER 2θ angles broadening of the diffraction peaks

• Ni3Fe phase formation
• the first order internal stresses

relaxation of the first order internal stresses the second order internal stresses

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88 90 92 94 96

Intensity (a.u.) 2 theta (degrees)

8 8 9 9 2 9 4 9 6

Ni3Fe Ni

88 89 90 91 92 93 94 95 2 θ (°)

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h

as milled

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+300°C/30min

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h

+330°C/1h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+330°C/3h +330°C/8h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+330°C/12h

ss

Intensity (a.u.)

88 90 92 94 96

Intensity (a.u.) 2 theta (degrees)

8 8 9 9 2 9 4 9 6

Ni3Fe Ni

88 89 90 91 92 93 94 95 2 θ (°)

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h

as milled

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h

as milled

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+300°C/30min

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+300°C/30min

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h

+330°C/1h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h

+330°C/1h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+330°C/3h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+330°C/3h +330°C/8h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+330°C/12h +330°C/8h

1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h

+330°C/12h

ss

Intensity (a.u.)

(311)

One annealing time Different milling time

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8 8 9 0 9 2 9 4 9 6

Intensity (a.u.) 2 theta (degrees)

88 90 9 2 9 4 9 6

88 89 90 91 92 93 94 95 2 θ (°)

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

ss

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 2 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 3 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 8 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 10 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 12 h

0 h 1 h

milled 14 h

0 h 1 h

milled 16 h

0 h 1 h

milled 20 h

0 h 1 h

milled 24 h

N i3Fe Ni

Intensity (a.u.)

8 8 9 0 9 2 9 4 9 6

Intensity (a.u.) 2 theta (degrees)

88 90 9 2 9 4 9 6

88 89 90 91 92 93 94 95 2 θ (°)

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

ss

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 2 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 3 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 8 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 10 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 12 h

0 h 1 h

milled 14 h

0 h 1 h

milled 16 h

0 h 1 h

milled 20 h

0 h 1 h

milled 24 h

8 8 9 0 9 2 9 4 9 6

Intensity (a.u.) 2 theta (degrees)

88 90 9 2 9 4 9 6

88 89 90 91 92 93 94 95 2 θ (°)

8 8 9 0 9 2 9 4 9 6

Intensity (a.u.) 2 theta (degrees)

88 90 9 2 9 4 9 6

88 89 90 91 92 93 94 95 2 θ (°)

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

ss

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 2 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 3 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 8 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 10 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 12 h

0 h 1 h

milled 14 h

0 h 1 h

milled 16 h

0 h 1 h

milled 20 h

0 h 1 h

milled 24 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

ss

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 2 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 2 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 3 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 3 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 8 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 8 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 10 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 10 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 12 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 12 h

0 h 1 h

milled 14 h

0 h 1 h

milled 14 h

0 h 1 h

milled 16 h

0 h 1 h

milled 16 h

0 h 1 h

milled 20 h

0 h 1 h

milled 20 h

0 h 1 h

milled 24 h

0 h 1 h

milled 24 h

N i3Fe Ni N i3Fe Ni

Intensity (a.u.)

(311)

One milling time Different annealing time

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2 θ (°)

8 9 0 9 2 9 4

Intensity (a.u.) 2 t h e t a ( d e g r e e s )

8 8 9 0 9 2 9 4 9 6

Intensity (a.u.) 88 89 90 91 92 93 94 95

ss

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

2 θ (°)

8 9 0 9 2 9 4

Intensity (a.u.) 2 t h e t a ( d e g r e e s )

8 8 9 0 9 2 9 4 9 6

Intensity (a.u.) 88 89 90 91 92 93 94 95

ss

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 1 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 12 h

milled 4 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

0 h 0.5 h 1 h 2 h 3 h 8 h

milled 6 h

(311)

θ β λ cos

2 1 ⋅

⋅ = k d

2 1

β - FWHM

d = 12 nm - 52 h milling 22 nm - 24 h milling

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0.3 0.6 0.9 1.2 100 200 300 400 500 600 700 800 ss 12 h

M2 (a.u.) T(

• C)

T

C(Ni)

T

C(Ni 3Fe)

T

C(Fe)

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3.8 4 4.2 4.4 4.6 4.8 5 10 15 20 25

not annealed 300°C/30min 330°C/1h 330°C/3h 330°C/8-12h

Ms (µBf.u.) milling time (hours) T = 4 K T = 300 K

*H. Hasegawa, J. Kanamori, J. Phys. Soc. Jap. 33 (1972) 1599

Fe1-xNix

in the reach nickel region*

x MFe

and

MNi=ct. MNi-Fe

when

Ni3Fe %

3.8 3.9 4.0 4.1 4.2 4.3 4.4 0.5 1 1.5 2 2.5 3 3.5

M (µB/f.u.) annealing time (hours) T = 300 K

ss 1 h 2 h 3 h 4 h 6 h λ 8 h x 10 h

• 12 h

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0h 3h 4h 8h 10h 12h

Velocity ( mm / s )

• 10

+10 0.96 1.00 Absorption ( % ) 0.96 1.00 Absorption ( % ) 0.97 1.00 Absorption ( % ) 0.98 1.00 Absorption ( % ) 0.99 1.00 Absorption ( % ) 0.98 1.00 Absorption ( % )

16h 24h 40h 48h 52h 52h Annealed

Velocity ( mm / s )

• 10

+10 0.99 1.00 Absorption ( % ) 0.99 1.00 Absorption ( % ) 0.98 1.00 Absorption ( % ) 0.98 1.00 Absorption ( % ) 0.98 1.00 Absorption ( % ) 0.98 1.00 Absorption ( % )

Speed (mm/s)

• 10 0 +10

Speed (mm/s)

• 10 0 +10

Absorption (%) Absorption (%)

20 40 60 80 100 10 20 30 40 50 60

Intensité Mossbauer (%) Temps de broyage (h) Ni3Fe α-Fe

Mössbauer intensity (%) milling time (hours)

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3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 10 20 30 40 50 60

4 K 295 K

M

s (µ B/f.u.)

Temps de broyage (h) recuit

10 20 30 40 50 60 28.0 28.5 29.0 29.5 30.0

Mean hyperfine field (T) Milling time, t m (hours)

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The particles morphology of the Ni75-Fe25 powders mixture (start sample - ss)

Ni particles Fe particles

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The particles morphology of the Ni-Fe powders mixture after 4h mechanical milling.

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The particles morphology of the Ni3Fe powders after 12h mechanical alloying.

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60µm 200µm

Ni Fe

initial mixed powders (ss) milled 12 hours

Energy dispersive X-ray analysis (EDX)

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0.0 2.0 4.0 6.0 8.0 10.0 12.0 0.5 1 1.5 2 2.5 3

milling time (hours) annealing time (hours)

0.0 2.0 4.0 6.0 8.0 10.0 12.0 0.5 1 1.5 2 2.5 3

milling time (hours) annealing time (hours) Ni Fe

3

M = const.

s

Ni+Fe+Ni Fe (Ni-Fe)

3

330 C

• T >330 C

1

• T >T

2 1

Milling – Annealing - Transformation (MAT) diagram

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2.50 TbCu7 + Th2Zn17 SmCo6.7Ti0.3Cu0.3 0.70 TbCu7 + Th2Zn17 SmCo6.7Cu0.3 1.90 TbCu7 + Th2Zn17 SmCo6.7Ti0.3 0.26 TbCu7 + Th2Zn17 SmCo7 MM + annealed 0.26 CaCu5 + Th2Zn17 SmCo6.7Ti0.3Cu0.3 0.20 CaCu5 + Th2Zn17 SmCo6.7Cu0.3 0.23 CaCu5 + Th2Zn17 SmCo6.7Ti0.3 0.12 CaCu5 + Th2Zn17 SmCo7 As-cast + annealed 0.15 TbCu7 SmCo6.7Ti0.3Cu0.3 0.10 TbCu7 SmCo6.7Cu0.3 0.12 TbCu7 SmCo6.7Ti0.3 0.05 TbCu7 + Th2Zn17 SmCo7 As-cast µ0Hc(T) Structure type Compound Type Table 2. Structural and room-temperature coercivity of Sm-Co-Cu-Ti intermetallic compounds

• M. Venkatesan, C. Jiang, J. M. D. Coey, J. Magn. Magn. Mater. 242-245 (2002) 1350

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Fe-Pt alloys are an important class of materials for permanent magnet applications because of their large magnetocrystalline anisotropy and good chemical stability. Small FePt particles may be suitable for future ultrahigh density magnetic recording media applications. FePt particle thin films had mainly relied on vacuum deposition techniques. We will present here few aspects concerning chemical synthesis of Fe-Pt alloys.

Chemical synthesis of FePt nanoparticles

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Chemical synthesis of FePt nanoparticles Sun et al. [S. Sun, C. B. Murray, D. Weller, L. Folks, A. Moser, Science 287 (2000)

1989 ], in order to prepare FePt nanoparticles, have used a

combination of oleic acid and oleyl amine to stabilise the monodisperse FePt colloids and prevent oxidation. The synthesis is based on the reduction of Pt(acac) (acac = acetylacetonate CH3COCHCOCH3) by a diol and the decomposition of Fe(CO)5 in high temperature solution. High resolution electron microscopy (HREM) studies have shown that FePt assembly on a thermally oxidized Si substrate are well separated i.e. no agglomeration occurs. Energy dispersive X-ray (EDX) spectroscopy confirms that the average nanocrystals are slightly iron rich, Fe52Pt48, and the interparticle spaces are about 2 nm.

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Chemical synthesis of FePt nanoparticles

• S. Sun, E. E. Fullerton, D. Weller, C. B. Murray, IEEE Trans. Magn. 37 (2001) 1239

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48

Hexane dispersions of FePt and Fe3O4 nanoparticles with mass ratio in the range 5:1 to 20:1 were mixed under ultrasonic agitation. Three-dimensional binary assembly hexane evaporation

• r addition of ethanol

the size of:

• FePt = 4 nm
• Fe3O4 clusters = 4- 12 nm

Ar+5%H2 650 °C

FePt+Fe3O4 FePt/Fe3Pt

• H. Zeng, J. Li, J. P. Liu, Z. L. Wang, S. Sun,

Nature 420 (2002) 395

Disordered fcc Ordered fct Soft fcc phase

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merci thank you