I. A. Al-Omari

Sultan Qaboos University, Masqaţ, Masqaţ, Oman

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Publications (123)169.58 Total impact

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    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.
    Applied Physics Letters 01/2014; 104(9):092407-092407-5. · 3.52 Impact Factor
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    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.
    Hyperfine Interactions 12/2013; · 0.21 Impact Factor
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    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.
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    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.
    Journal of Magnetism and Magnetic Materials 09/2013; 341:165–172. · 2.00 Impact Factor
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    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.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 09/2013; · 1.19 Impact Factor
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    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.
    Materials Chemistry and Physics 06/2013; 140(1):97. · 2.07 Impact Factor
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    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.
    Acta Materialia 01/2013; · 3.94 Impact Factor
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    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)).
    Inorganic Chemistry 07/2012; 51(15):8241-53. · 4.59 Impact Factor
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    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.
    Dalton Transactions 01/2012; 41(8):2500-14. · 4.10 Impact Factor
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    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.
    Hyperfine Interactions 08/2011; · 0.21 Impact Factor
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    ABSTRACT: The effect of depositing FeO nanoparticles with a diameter of 10 nm onto the surface of MgB(2) thin films on the critical current density was studied in comparison with the case of uncoated MgB(2) thin films. We calculated the superconducting critical current densities (J(c)) from the magnetization hysteresis (M-H) curves for both sets of samples and found that the J(c) value of FeO-coated films is higher at all fields and temperatures than the J(c) value for uncoated films, and that it decreases to ~10(5) A/cm(2) at B = 1 T and T = 20 K and remains approximately constant at higher fields up to 7 T.
    Beilstein Journal of Nanotechnology 01/2011; 2:809-13. · 2.37 Impact Factor
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    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.
    FIFTH SAUDI PHYSICAL SOCIETY CONFERENCE (SPS5); 01/2011
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    ABSTRACT: The magnetism of the vanadium (001) surface has been a controversial subject on both theoretical and experiment fronts. Both strongly ferromagnetic and paramagnetic phases were reported. We have used the first principle full-potential linearized-augmented plane waves (FP-LAPW) as implemented in WIEN2k package to study the magnetic properties of strained surfaces of vanadium films as a function of film thickness. We found that for films thicker than about 11 monolayers, the magnetism of the strained surfaces converge to a constant value of about 0.15μB. Introduction of Fe monolayers and impurities at the centre of the films affects the magnetic structure of thin films but has no influence on the surface magnetism of thicker films. For Fe monolayers positioned at the centre of thick films, the Fe atoms maintain magnetic moment of order 0.86μB, a quadruple splitting of order -0.3 mm/s and a small negative isomer shift, while an Fe impurity has vanishing hyperfine fields and magnetic moment. In addition we have varied the location of the Fe monolayer and impurity within the V films and found that their position affects the surface magnetism.
    Journal of Physics Conference Series 05/2010; 217(1):012117.
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    ABSTRACT: The magnetocaloric properties of cobalt ferrite nanoparticles were investigated to evaluate the potential of these materials as magnetic refrigerants. Nanosized cobalt ferrites were synthesized by the method of sol–gel combustion. The nanoparticles were found to be spherical with an average crystallite size of 14 nm. The magnetic entropy change (ΔS m) calculated indirectly from magnetization isotherms in the temperature region 170–320K was found to be negative, signifying an inverse magnetocaloric effect in the nanoparticles. The magnitudes of the ΔS m values were found to be larger when compared to the reported values in the literature for the corresponding ferrite materials in the nanoregime.
    Applied Physics A 05/2010; 99(2):497-503. · 1.69 Impact Factor
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    ABSTRACT: We present results on the thermal dependence of the magnetization above ambient conditions of ZnFe2O4 nanoferrites having different degrees of inversion (c∼0.05–0.40) and grain sizes (D∼6–50nm). The disordered ferrites present a net magnetization in the 400–510K range that mainly depends on the degree of inversion. The reciprocal magnetization deviate from different temperature values of the linear behavior showed at high temperatures. Our results show that, contrary to similar nanoferrite systems, a simple scaling law cannot be applied to explain the Néel temperature TN dependency with the grain size. These results can be interpreted in terms of the lack of correlation between size and inversion that occurs in ZnFe2O4 and the strong TN dependence on the superexchange JAB interaction strength. A model assuming a random distribution of superexchange interactions can reproduce the Curie–Weiss temperature and the saturation magnetization values of the disordered ferrites.
    Journal of Alloys and Compounds 01/2010; 495(2):506-508. · 2.73 Impact Factor
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    ABSTRACT: Mn1−xZnxFe2O4 nanoparticles (x = 0 to 1) were synthesized by the wet chemical co-precipitation technique. X-ray diffraction and transmission electron microscopy and high resolution transmission electron microscopy were effectively utilized to investigate the different structural parameters. The ac conductivity of nanosized Mn1−xZnxFe2O4 were investigated as a function of frequency, temperature and composition. The frequency dependence of ac conductivity is analysed by the power law σ(ω)ac = Bωn which is typical for charge transport by hopping or tunnelling processes. The temperature dependence of frequency exponent n was investigated to understand the conduction mechanism in different compositions. The conduction mechanisms are mainly based on polaron hopping conduction.
    Journal of Physics D Applied Physics 07/2009; 42(16):165005. · 2.53 Impact Factor
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    ABSTRACT: Magnesium-substituted nickel–chrome ferrites have been studied using X-ray diffraction and Mössbauer spectroscopy. A single cubic spinel phase was obtained in the range 0.0 ≤ x ≤ 0.4. The lattice parameter was found to decrease with the increase of Mg concentration. The Mössbauer spectra measured at 295 and 78K of all samples showed magnetic patterns interpreted in term of the tetrahedral and octahedral sites occupancies. The magnetic hyperfine field of both sites decrease with the increase of the Mg concentration. The magnetic properties as a function of the Mg concentration have been explained on the basis of the cation distribution among the two crystallographic sites driven from the Mössbauer measurements.
    05/2009: pages 519-524;
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    ABSTRACT: The temperature and frequency dependence of dielectric permittivity and dielectric loss of nanosized Mn(1-x)Zn(x)Fe(2)O(4) (for x = 0, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The impact of zinc substitution on the dielectric properties of the mixed ferrite is elucidated. Strong dielectric dispersion and broad relaxation were exhibited by Mn(1-x)Zn(x)Fe(2)O(4). The variation of dielectric relaxation time with temperature suggests the involvement of multiple relaxation processes. Cole-Cole plots were employed as an effective tool for studying the observed phenomenon. The activation energies were calculated from relaxation peaks and Cole-Cole plots and found to be consistent with each other and indicative of a polaron conduction.
    Journal of Physics Condensed Matter 04/2009; 21(14):146006. · 2.22 Impact Factor
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    ABSTRACT: The electronic and magnetic structures of Fe–V alloys are calculated using the discrete-variational and full-potential linearized-augmented-plane wave methods. The derived hyperfine properties at Fe sites are studied against the number of Fe atoms in the neighbouring shells. As expected the magnetic hyperfine field depends strongly on the number of Fe atoms in the first and second shells of neighbours while its dependence on the variation of atoms in the third shell is weak. The calculated distribution of the magnetic hyperfine fields at the Fe sites, are compared to the experimental data of Krause et al. (Phys Rev B 61:6196–6204, 2000). The contact charge densities and the magnetic moments are also calculated. It was found that the contact charge density increases with increasing V contents and this leads to negative isomer shift on addition of V.
    04/2009: pages 459-464;

Publication Stats

307 Citations
169.58 Total Impact Points

Institutions

  • 2002–2014
    • Sultan Qaboos University
      • Department of Physics
      Masqaţ, Masqaţ, Oman
  • 2011
    • Wichita State University
      Wichita, Kansas, United States
  • 2009
    • Cochin University of Science and Technology
      • Department of Physics
      Cochin, Kerala, India
  • 2004–2006
    • University of Khartoum
      • Department of Physics
      Khartoum, Khartoum, Sudan
  • 2000–2002
    • Yarmouk University
      • Department of Physics
      Irbid, Irbid, Jordan
  • 1997–2002
    • Jordan University of Science and Technology
      • Department of Physics
      Arbēla, Irbid, Jordan
  • 1994–2001
    • University of Nebraska at Lincoln
      • Department of Physics and Astronomy
      Lincoln, NE, United States
  • 1998
    • Bar Ilan University
      • Department of Physics
      Ramat Gan, Tel Aviv, Israel
  • 1995
    • University of Delaware
      • Department of Physics and Astronomy
      Newark, DE, United States