I. A. Al-Omari

Sultan Qaboos University, Masqaţ, Muḩāfaz̧at Masqaţ, Oman

Are you I. A. Al-Omari?

Claim your profile

Publications (119)152.02 Total impact

  • Dataset: JAP
    No preview · Dataset · Apr 2016
  • Dataset: JAP
    No preview · Dataset · Apr 2016
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Mixed valence manganite system with monovalent sodium substituted lanthanum manganites form the basis of the present work. Lanthanum manganites belonging to the series La1−xNaxMnO3 with x=0.5–0.9 were synthesized using modified citrate gel method. Variation of lattice parameters and unit cell volume with Na concentration were analyzed and the magnetization measurements indicated ferromagnetic ordering in all samples at room temperature. Low temperature magnetization behavior indicated that all samples exhibit antiferromagnetism along with ferromagnetism and it has also been observed that antiferromagnetic ordering dominates ferromagnetic ordering as concentration is increased. Evidence for such a magnetic inhomogeneity in these samples has been confirmed from the variation in Mn3+/Mn4+ ion ratio from X-ray Photoelectron Spectroscopy and from the absorption peak studies using Ferromagnetic Resonance Spectroscopy.
    Full-text · Article · Oct 2015 · Journal of Magnetism and Magnetic Materials
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Magnetization reversal of antiferromagnetically coupled (AFC) soft and hard (Co/Pd) multilayers was studied as a function of temperature. While the hard [Co(0.3 nm)/Pd(0.8 nm)]×10 was kept unchanged, the softness of the [Co(t)/Pd(0.8 nm)]×3 was controlled by varying the thickness t of the Co sublayer. Clear two-step hysteresis loops were observed for all the investigated multilayers with t ranging between 0.4 and 1 nm. The spin reorientation of the soft layer magnetization from in-plane direction to out-of-plane direction was investigated from 50 to 300 K. The antiferromagnetic field H AFC measured from the shift of the minor hysteresis loop reveals a good agreement to the quantum-well model. From the out-of-plane hysteresis loop of the uncoupled soft layer, its magnetization shows an in-plane orientation for t ≥ 0.6 nm. The strong H AFC helps to induce an out-of plane orientation of the soft layer with a linear decrease of its coercivity with temperature. These investigated structures show the possibility to reduce the unwanted stray field and improving the out-of-plane anisotropy even for relatively thicker soft layer.
    Full-text · Article · Aug 2015 · Journal of Applied Physics
  • [Show abstract] [Hide abstract] ABSTRACT: The incorporation of nanoparticles of iron in a natural rubber matrix leads to flexible magnetorheological (MR) materials. Rod-shaped MR elastomers based on natural rubber and nanosized iron have been moulded both with and without the application of an external magnetic field during curing. These MR elastomer rods and filler material were characterized by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. Magnetic properties were investigated by using vibrating sample magnetometry. Microactuation studies were carried out by employing a laser Doppler vibrometer. It is seen that microactuation of field cured samples have been enhanced by two times when compared with that of zero field cured samples. The effect of alignment of magnetic particles during field-assisted curing was also studied by using a dynamic mechanical analyzer. A plausible model is put forwarded to explain the observed enhancement of actuation for field cured samples.
    No preview · Article · Jun 2015 · Bulletin of Materials Science
  • [Show abstract] [Hide abstract] ABSTRACT: Thin films of Co-Fe-Si were vacuum evaporated on pre-cleaned float glass substrates employing thermal evaporation. The films were subsequently irradiated with 100 MeV Ag+7 ions at fluences of 1×1011, 1×1012 and 1×1013 ions/cm2. The pristine and irradiated samples were subjected to surface analysis using Atomic Force Microscopy (AFM), Vibrating Sample Magnetometry (VSM) and Magneto Optic Kerr Effect (MOKE) measurements. The as deposited film has a root mean square roughness (Rq) of 8.9 nm and an average roughness of (Ra) 5.6 nm. Irradiation of the as deposited films with 100 MeV Ag7+ ions modifies the surface morphology. Irradiating with ions at fluences of 1×1011 ions/cm2 smoothens the mesoscopic hill-like structures, and then, at 1×1012 ions/cm2 new surface structures are created. When the fluence is further increased to 1×1013 ions/cm2 an increase in the surface roughness is observed. The MOKE loop of as prepared film indicated a squareness ratio of 0.62. As the film is irradiated with fluences of 1×1011 ions/cm2, 1×1012 ions/cm2 and 1×1013 ions/cm2 the squareness ratio changes to 0.76, 0.8 and 0.86 respectively. This enhancement in squareness ratio towards 1 is a typical feature when the exchange interaction starts to dominates the inherent anisotropies in the system. The variation in surface magnetisation is explained based on the variations in surface roughness with swift heavy ion (SHI) irradiation.
    No preview · Article · Nov 2014 · Journal of Magnetism and Magnetic Materials
  • Source
    Full-text · Dataset · Apr 2014
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300 K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J·kg−1·K−1 was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300 K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300 K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62 K at 280 K.
    Full-text · Article · Mar 2014 · Applied Physics Letters
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Abstract The mechanosynthesis of cubic γ -phase pure BiFeO3 and Ti4+-doped BiFeO3 nanocrystalline particles and their preliminary characterization with magnetic measurements and M¨ossbauer spectroscopy are reported. The BiFeO3 nanoparticles (5–40 nm) were prepared by heating a 48 h pre-milled 1:1 molar mixture of α-Bi2O3 and α-Fe2O3 at 400 ◦C for (1 h). Doping α-Fe2O3in the initial mixture of reactants with Ti4+ was found to lead to the formation of Ti4+-doped BiFeO3 nanoparticles by milling the reactants for 32 h. The magnetization of the BiFeO3 nanoparticles is found to be tripled under a maximum external field of 1.35 T and their magnetic hardness increases by ∼15 times relative to those of the corresponding bulk. The Ti4+-doped BiFeO3 nanoparticles exhibit higher magnetization relative to the pure ones. These observations are related to the spiral modulated spin structure of the compound. The M¨ossbauer data show ∼12 % of the BiFeO3 nanocrystalline particles to be superparamagnetic having blocking temperatures of less than 78 K. The quadrupole shift values of the magnetic spectral component favor the cubic structural symmetry. These observations were mainly associated with possible collective magnetic excitations as well as transverse relaxation of canted surface spins. The Ti-doped BiFeO3 nanoparticles gave statistically-poor M¨ossbauer spectra with no signs of a superparamagnetic behavior.
    Full-text · Article · Dec 2013 · Hyperfine Interactions
  • [Show abstract] [Hide abstract] ABSTRACT: Ultra thin films based on CoFe were prepared from a composite target employing thermal evaporation. The microstructure of the films was modified by thermal annealing. The relationship between microstructure and magnetic properties of the films was investigated using techniques like glancing angle X-ray diffraction (GXRD), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The GXRD and TEM investigations showed an onset of crystallization of CoFe at around 373 K. The magnetic softness of the films improved with thermal annealing but at higher annealing temperature it is found to be deteriorating. Annealing induced modification of surface morphology of the alloy thin films was probed by atomic force microscopy (AFM). Surface smoothening was observed with thermal annealing and the observed magnetic properties correlate well with surface modifications induced by thermal annealing.
    No preview · Article · Dec 2013 · Surface and Coatings Technology
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: A systematic study has been made of the initial corrosion products which form on mild steel capons exposed near the coastal region of Oman and at some industrial areas. The phases and compositions of the products formed at different periods of exposure were examined by using Mössbauer spectroscopy (295 and 78 K) and X-ray diffraction (XRD) techniques. The results show that lepidocorcite and maghemite are early corrosion products and goethite starts to form after 2 months of metal exposure to the atmosphere. Akaganeite is an early corrosion product but it forms in marine environments only, which reflects the role of chlorine effect in the atmosphere. The 12 months coupons showed the presence of goethite, lepidocorcite and maghemite, but no akaganeite being seen in the products of one of the studied areas.
    Full-text · Dataset · Oct 2013
  • [Show abstract] [Hide abstract] ABSTRACT: Co–Fe–Si based films exhibit high magnetic moments and are highly sought after for applications like soft under layers in perpendicular recording media to magneto-electro-mechanical sensor applications. In this work the effect of annealing on structural, morphological and magnetic properties of Co–Fe–Si thin films was investigated. Compositional analysis using X-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a native oxide surface layer consisting of oxides of Co, Fe and Si on the surface. The morphology of the as deposited films shows mound like structures conforming to the Volmer–Weber growth model. Nanocrystallisation of amorphous films upon annealing was observed by glancing angle X-ray diffraction and transmission electron microscopy. The evolution of magnetic properties with annealing is explained using the Herzer model. Vibrating sample magnetometry measurements carried out at various angles from 0° to 90° to the applied magnetic field were employed to study the angular variation of coercivity. The angular variation fits the modified Kondorsky model. Interestingly, the coercivity evolution with annealing deduced from magneto-optical Kerr effect studies indicates a reverse trend compared to magetisation observed in the bulk. This can be attributed to a domain wall pinning at native oxide layer on the surface of thin films. The evolution of surface magnetic properties is correlated with morphology evolution probed using atomic force microscopy. The morphology as well as the presence of the native oxide layer dictates the surface magnetic properties and this is corroborated by the apparent difference in the bulk and surface magnetic properties.
    No preview · Article · Sep 2013 · Journal of Magnetism and Magnetic Materials
  • [Show abstract] [Hide abstract] ABSTRACT: We have investigated the effects of swift heavy ion irradiation on thermally evaporated 44 nm thick, amorphous Co77Fe23 thin films on silicon substrates using 100 MeV Ag7+ ions fluences of 1 × 1011 ions/cm2, 1 × 1012 ions/cm2, 1 × 1013 ions/cm2, and 3 × 1013 ions/cm2. The structural modifications upon swift heavy irradiation were investigated using glancing angle X-ray diffraction. The surface morphological evolution of thin film with irradiation was studied using Atomic Force Microscopy. Power spectral density analysis was used to correlate the roughness variation with structural modifications investigated using X-ray diffraction. Magnetic measurements were carried out using vibrating sample magnetometry and the observed variation in coercivity of the irradiated films is explained on the basis of stress relaxation. Magnetic force microscopy images are subjected to analysis using the scanning probe image processor software. These results are in agreement with the results obtained using vibrating sample magnetometry. The magnetic and structural properties are correlated.
    No preview · Article · Sep 2013 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: We report on the mechanosynthesis of single-phased EuCr1-xFexO3 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) nanocrystalline particles (~ 20-50 nm) at temperatures that are significantly lower than those at which the corresponding bulk materials are conventionally synthesized and their structural and magnetic characterization. The average crystallite size was found to decrease, the lattice parameters increase, and the unit cell gets more distorted with increasing x. All samples showed weak ferromagnetism due to spin canting. The Curie temperatures, though increase with increasing x, are significantly lower than those of the corresponding bulk materials. Simple Curie-Weiss fits for the paramagnetic susceptibilities were found to be more physically plausible relative to fits where Vleck-type contributions to the paramagnetic susceptibilities due to Eu3+ ionic sublattices, that are separate from of the Cr3+/Fe3+ ones, were assumed. The non-existence of such separate Eu3+ and Cr3+/Fe3+ sublattices was further supported by 151Eu Mössbauer spectra of the nanoparticles which favor a non-equilibrium cation distribution wherein a considerable amount of Eu3+ and Cr3+/Fe3+ ions exchange their normal dodecahedral and octahedral perovskite-related sites, respectively. The supertransferred hyperfine magnetic field at the site of the 151Eu nuclei, induced by neighboring Cr3+/Fe3+ ions, was found to be considerably larger for B-site nuclei than for A-site ones. The antisite behavior concluded in this study is consistent with 57Fe Mössbauer spectral analysis of the nanoparticles that favor the presence of the majority of the Fe3+ ions at the usual B-sites and minority Fe3+ ions either at the A-sites or at B-sites with Eu3+ / Cr3+ nearest B-site neighbors. The relative site occupancies associated with the cationic site exchange inferred from both the 151Eu and 57Fe Mössbauer spectra are remarkably consistent.
    Full-text · Article · Jul 2013 · Acta Materialia
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Spinel-related Mg1+2xSbxFe2-3xO4 samples (x = 0.0, 0.05, 0.10, 0.15, 0.20, and 0.30) prepared using the conventional double sintering technique were investigated using 57Fe Mössbauer spectroscopy and magnetic measurements. Mössbauer spectra favor a cationic distribution of the form (MgdFe1-d)A[Mg1+2x -dSbxFe1+d-3x]BO4 among the tetrahedral-A and octahedral-B sites of the spinel structure. The cation distribution parameter (d) was found to vary with the Sb5+ concentration (x). The Mössbauer hyperfine magnetic fields at both sites and the Curie temperatures of the ferrites decrease as x increases. This was attributed to gradual weakening in the magnetic exchange interaction as more Fe3+ ions are substituted by diamagnetic Sb5+ and Mg2+ ones. The sample with x = 0.30 exhibits short range magnetic order due to cationic clustering and/or superparamagnetism. The magnetization of all samples was found to be temperature-dependent implying that d depends on temperature in addition to x. At low temperatures the substituted ferrites (x not equal to 0.0) unexpectedly exhibit higher magnetization values relative to that of the pure ferrite MgFe2O4. This behavior, while at variance with the Néel’s model for ferrimagnetism, is explicable in terms of the spin canting mechanism proposed in the YafeteKittel model.
    Full-text · Article · Jun 2013 · Materials Chemistry and Physics
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The mechanosynthesis of cubic γ-phase pure BiFeO3 and Ti4+-doped BiFeO3 nanocrystalline particles and their preliminary characterization with magnetic measurements and Mössbauer spectroscopy are reported. The BiFeO3 nanoparticles (5–40 nm) were prepared by heating a 48 h pre-milled 1:1 molar mixture of α-Bi2O3 and α-Fe2O3 at 400 °C for (1 h). Doping α-Fe2O3 in the initial mixture of reactants with Ti4+ was found to lead to the formation of Ti4+-doped BiFeO3 nanoparticles by milling the reactants for 32 h. The magnetization of the BiFeO3 nanoparticles is found to be tripled under a maximum external field of 1.35 T and their magnetic hardness increases by ∼15 times relative to those of the corresponding bulk. The Ti4+-doped BiFeO3 nanoparticles exhibit higher magnetization relative to the pure ones. These observations are related to the spiral modulated spin structure of the compound. The Mössbauer data show ∼12 % of the BiFeO3 nanocrystalline particles to be superparamagnetic having blocking temperatures of less than 78 K. The quadrupole shift values of the magnetic spectral component favor the cubic structural symmetry. These observations were mainly associated with possible collective magnetic excitations as well as transverse relaxation of canted surface spins. The Ti-doped BiFeO3 nanoparticles gave statistically-poor Mössbauer spectra with no signs of a superparamagnetic behavior.
    Full-text · Article · Apr 2013 · Hyperfine Interactions
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 Å) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and Mössbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and Mössbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ↔ (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the μ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(μ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).
    Full-text · Article · Jul 2012 · Inorganic Chemistry
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The two potentially tridentate and monoprotic Schiff bases acetylpyridine benzoylhydrazone (HL(1)) and acetylpyridine 4-tert-butylbenzoylhydrazone (HL(2)) demonstrate remarkable coordination versatility towards iron on account of their propensity to undergo tautomeric transformations as imposed by the metal centre. Each of the pyridyl aroylhydrazone ligands complexes with the ferrous or ferric ion under strictly controlled reaction conditions to afford three six-coordinate mononuclear compounds [Fe(II)(HL)(2)](ClO(4))(2), [Fe(II)L(2)] and [Fe(III)L(2)]ClO(4) (HL = HL(1) or HL(2)) displaying distinct colours congruent with their intense CT visible absorptions. The synthetic manoeuvres rely crucially on the stoichiometry of the reactants, the basicities of the reaction mixtures and the choice of solvent. Electrochemically, each of these iron compounds exhibits a reversible metal-centred redox process. By all appearances, [Fe(III)(L(1))(2)]ClO(4) is one of only two examples of a crystallographically elucidated iron(III) bis-chelate compound of a pyridyl aroylhydrazone. Several pertinent physical measurements have established that each of the Schiff bases stabilises multiple spin states of iron; the enolate form of these ligands exhibits greater field strength than does the corresponding neutral keto tautomer. To the best of our knowledge, [Fe(III)(L(1))(2)]ClO(4) and [Fe(III)(L(2))(2)]ClO(4) are the first examples of ferric spin crossovers of aroylhydrazones. Whereas in the former the spin crossover (SCO) is an intricate gradual process, in the latter the (6)A(1)↔(2)T(2) transition curve is sigmoidal with T(½)∼280 K and the SCO is virtually complete. As regards [Fe(III)(L(1))(2)]ClO(4), Mössbauer and EPR spectroscopic techniques have revealed remarkable dependence of the spin transition on sample type and extent of solvation. In frozen MeOH solution at liquid nitrogen temperature, both iron(III) compounds exist wholly in the doublet ground state.
    Full-text · Article · Jan 2012 · Dalton Transactions
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The orthoferrimanganites Nd0.65Sr0.35FexMn1−xO3 (x = 0.1, 0.3, 0.6) have been investigated using XRD, MÖssbauer spectroscopy, magnetization and conductivity techniques. The XRD reflections exhibit single phase structure. The paramagnetic–superparamagnetic‐magnetic transitions were observed from MÖssbauer spectra and magnetization measurements in the temperature range from the liquid nitrogen to the room temperature. The conductivity study of the x = 0.1 and 0.3 show semiconducting behavior with more pronounced conductivity for the latter leading to an activation energy double that of the former. The effect of the Fe substitution on the electronic and magnetic properties was analyzed and discussed.
    Full-text · Conference Paper · Oct 2011
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: : We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-vanadium superlattice consisting of three Fe monolayers and nine V monolayers. The contact charge density ({\rho}), the contact hyperfine field (Bhf) and the electronic field gradient (EFG) at the Fe sites for different H locations and H fillings are calculated using the first principle full-potential linear-augmented-plane-wave (FP-LAPW) method . It is found that sizeable changes in the hyperfine properties are obtained only when H is in the interface region.
    Full-text · Article · Aug 2011 · Hyperfine Interactions

Publication Stats

915 Citations
152.02 Total Impact Points

Institutions

  • 2003-2015
    • Sultan Qaboos University
      • Department of Physics
      Masqaţ, Muḩāfaz̧at Masqaţ, Oman
  • 1994-2009
    • University of Nebraska at Lincoln
      • • Nebraska Center for Materials and Nanoscience
      • • Department of Physics and Astronomy
      Lincoln, Nebraska, United States
  • 2000
    • Yarmouk University
      • Department of Physics
      Arbēla, Irbid, Jordan
  • 1997-1998
    • Jordan University of Science and Technology
      • Department of Physics
      Arbēla, Irbid, Jordan