Structural and Magnetic properties of α-Fe 2 O 3 Nanoparticles د.محمد عبد الله ولد محمد الأمين قسم الفيزياء كلية العلوم جامعة الإمام محمد بن سعود الإسلامية SPS 4th annual meeting November Riyadh

 Introduction  Experimental  Results  Conclusions Outline

Introduction Maghemite (γ-Fe 2 O 3 )Hematite (α-Fe 2 O 3 )Magnetite (Fe3O4)  Magnetic iron oxides nanoparticles have attracted an increasing interest in the fields of nanoscience and nanotechnology. Sol–gel process Microemulsion technique Forced hydrolysis method Chemical 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 structure R3c space group a= Å c= Å T<T M = 260 K: antiferromagnetic 260 K<T<950 K: weak ferromagnetic (spin canting) T>T N = 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 Properties Mössbauer Spectrometry Hysterisis Loops Structure and Morphology XRD, SEM and FT-IR Experimental

Mössbauer Spectrometry Information obtained from Mössbauer : - Magnetic hyperfine characteristics of iron oxide phases. - Information concerning the valence state of 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 emission

Results X-ray diffraction  All Bragg peaks were only assigned to the presence of α-Fe 2 o 3.  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  Δa/a0 and Δc/c0 were found to be positive for all milled samples indicating a lattice expansion. -The variation have the same tendancy indicating anisotropic expansion.  The average grain size decreases  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 to access at possible structural changes of the hematite particle during the milling process ?  No new peaks in the milled spectra  Important changes in the relative intensities and broadening, In agreement with XRD results

Magnetic properties Mössbauer Spectrometry Hysterisis Loops

Mössbauer at room temperature Only one sextet  = 0.37 mm/s  Q = -0.2 mm/s H = 51.3 T Bulk  -Fe 2 O 3 Micrometric (100%) First sextet  = 0.37 mm/s  Q = -0.2 mm/s H = 50.2 T Micrometric  -Fe 2 O 3 (52%) second sextet  = 0.35 mm/s H = 45 T Nanometric  -Fe 2 O 3 (48%) 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(Fe 3 O 4 ) nanoparticles for MRI diagnosis. Maghemite (γ-Fe 2 O 3 )Hematite (α-Fe 2 O 3 )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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