Structural and Magnetic properties of α-Fe2O3 Nanoparticles

األمين. محمد ولد الله عبد محمد دالفيزياء قسمالعلوم كلية

اإلسالمية سعود بن محمد اإلمام جامعةE-mail : mamamin@imamu.edu.sa /leminej@yahoo.com

SPS 4th annual meeting11-12 November 2008 - Riyadh

Introduction

Experimental

Results

Conclusions

Outline

Introduction

Maghemite (γ-Fe2O3) Hematite (α-Fe2O3) Magnetite (Fe3O4)

Magnetic iron oxides nanoparticles have attracted an increasing interest in the fields of nanoscience and nanotechnology.

Sol–gel processMicroemulsion techniqueForced hydrolysis methodChemical precipitation

Ball milling :has been used by several groups:

the phase transformations of α-Fe2O3 to γ-Fe2O3 or vice versa.

Recently L.C.Sanchez et al Physica B 389 (2007) : by milling in ethanol and in air (the jars were opened to the atmosphere)

Rhombohedrally centered hexagonal structureR3c space groupa=5.0356 Åc=13.7489 ÅT<TM = 260 K: antiferromagnetic

260 K<T<950 K: weak ferromagnetic (spin canting)T>TN = 950 K: paramagnetic

Aim of this work

Production of hematite nanoparticles without phase transformation by dry milling (the jars were

closed) ?

-Structural and magnetic properties

Mechanical Alloying

Magnetic PropertiesStructure and Morphology

Mössbauer Spectrometry Hysterisis Loops XRD, SEM and FT-IR

Experimental

Mössbauer Spectrometry

Information obtained from Mössbauer :

- Magnetic hyperfine characteristics of ironoxide phases.- Information concerning the valence stateof iron atoms.- Relative abundance of each component

Samples preparation

-Commercial α-Fe2O3 powder -Fritsch-P6 – Intensity 250rpm

-Stainless steel balls(10 and 15 mm in diameter) . -The sample to balls weight ratio 1:10

-Different milling times

Information obtained from Mössbauer: Mössbauer effect is the recoil-free emission and resonant absorption of gamma ( γ) rays from the nuclei of certain radioactive isotopes such as 57Fe

Results

X-ray diffraction

All Bragg peaks were only assigned to the presence of α-Fe2o3.

The diffraction peaks became broader and their relative intensity decreases.

The peak broadening can be caused by both a reduction in crystallite size and an increase in lattice strain ???

In order to obtain these parameters (particles size and strain), a qualitative and quantitative phase analyses using the Rietveld method have been performed.

Visual observation : the color of the samples remains red (no new phase).

Rietveld Analysis

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 10 20 30 40 50

Milling time (H)

Fra

cti

on

al

va

ria

tio

n o

f u

nit

ce

ll

0

0

0 a

aa

a

a

0

0

0 c

cc

c

c

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60

Milling time (h)

Av

era

ge

pa

rtic

le s

ize

(n

m)

Δa/a0 and Δc/c0 were found to be positivefor all milled samples indicating a lattice expansion.-The variation have the same tendancy indicating anisotropic expansion.

The average grain size decreases

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60

milling time(h)

Mic

ros

tra

in(%

)

The microstrain increase with milling time

-Using FullProf program

-The fitting is performed by a least square method.

-Information given by Rietveld : lattices parameteres,

microstrain average particle size

FT-IR measurements

0

200

400

600

800

1000

1200

1400

3500 3000 2500 2000 1500 1000 500

Wave number (cm -1)

Tra

nsm

itta

nce

0 h

6 h

12 h

0

200

400

600

800

1000

1200

1400

3500 3000 2500 2000 1500 1000 500

Wave number (cm -1)

Tra

nsm

itta

nce

0 h

6 h

12 h

to access at possible structural changes of the hematite particle during the milling process ?

No new peaks in the milled spectraImportant changes in the relative intensities and broadening,

In agreement with XRD results

Magnetic properties

Mössbauer Spectrometry Hysterisis Loops

Mössbauer at room temperature

Unmilled

0.88

0.9

0.92

0.94

0.96

0.98

1

1.02

-15 -10 -5 0 5 10 15Velocity (mm/s)

Tra

nsm

issi

on

(a.

u)

48H

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

1.01

-15 -10 -5 0 5 10 15

Velocity (mm/s)

Tra

nsm

issi

on

(a.u

)

Only one sextet

= 0.37 mm/s

Q = -0.2 mm/s

H = 51.3 T

Bulk -Fe2O3

Micrometric (100%)

First sextet

= 0.37 mm/s

Q = -0.2 mm/s

H = 50.2 T

Micrometric -Fe2O3(52%)

second sextet

= 0.35 mm/s

H = 45 T

Nanometric -Fe2O3(48%)

H (kOe)

-20 -15 -10 -5 0 5 10 15 20

M (em

u/g)

-60

-40

-20

0

20

40

60

S0S4

T=100K

Hysteresis loops

- -The magnetic hysteresis loops for both samples are

typical of ferromagnet;

-Increase of saturation with decreasing size

Conclusions

-Mechanical alloying of hematite micrometric powder processing can be used for the synthesis of hematite nanoparticles without phase transformation after milling from 1 up to 48h.

-An expansion of lattices parameters due to the increasing of microstrain induced by ball milling

-Mössbauer spectra show that are two component for the milled sample one attributed to the hematite nanoparticles and other due to micrometric hematite .

-XRD, FT - IR and Mössbauer : show that are no phase changing during the milling

Mohamed Alameen et al, (Submitted to International Journal of Nanosciences)

Perspective

-Thermal analysis are in progress

-Particle size obtained by XRD ??? Furthers measurement of nanoparticles size will be conducted with others methods such as TEM and Brunauer – Emmett- Teller method (BET).

-Magnetic measurements (I will do more analysis on VSM measurements) .

New project :Gamma irradiation preparation of magnetite(Fe3O4) nanoparticles for MRI diagnosis.

Maghemite (γ-Fe2O3) Hematite (α-Fe2O3) Magnetite (Fe3O4)

Acknowledgments

This work was supported financially by King Abdulaziz City for Sciences and technology (KACST).

Collaborations:

Dr A.Alyemani , R. Msalam and S. Mufti (KACST)

Pr M.Sajieddine, Materials sciences group (Sultan Moulay Slimane University,Béni-Mellal (Morroco).

Pr K.Ziq , Physics department, KFUPM

Dr M.Bououdina,Physics department, University of Bahrain, Kingdom of Bahrain

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