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Sökning: WFRF:(Moubah Reda)

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1.
  • Moubah, Reda, et al. (författare)
  • Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
  • 2016
  • Ingår i: Physical Review Applied. - : American physical society. - 2331-7019. ; 5:4
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.
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2.
  • Moubah, R., et al. (författare)
  • Origin of the anomalous temperature dependence of coercivity in soft ferromagnets
  • 2014
  • Ingår i: Applied Physics Reviews. - : American Institute of Physics (AIP). - 1931-9401. ; 116:5, s. 053906-
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the origin of the anomalous temperature dependence of coercivity observed in some soft ferromagnets by studying the magnetic and electronic properties of FeZr films doped using ion implantation by H, He, B, C, and N. The anomalous increase of the coercivity with temperature was observed only in the C- and B-doped samples. Using x-ray photoelectron spectroscopy, we show that the anomalous behavior of the coercivity coincides with the occurrence of an electron charge transfer for those implanted samples. The origin of the anomaly is discussed in terms of (i) magnetic softness, (ii) nature of the Fe-C and -B covalent bonds, and (iii) large charge transfer. (C) 2014 AIP Publishing LLC.
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3.
  • Zamani, A., et al. (författare)
  • Magnetic properties of amorphous Fe93Zr7 films : Effect of light ion implantation
  • 2015
  • Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 117:14
  • Tidskriftsartikel (refereegranskat)abstract
    • The Curie temperature (Tc) of amorphous FeZr alloys can be greatly enhanced by doping with light elements. In this investigation, ion implantation is used to dope Fe93Zr7 thin films with H, He, B, C, and N. Extended X-ray absorption fine structure measurements confirm that the amorphous structure is preserved upon implantation for all samples, except for the N-implanted sample which is partially crystallized. The Curie temperature increases from 124 K for the pristine FeZr sample to about 400 K for the (FeZr)B0.11 sample. The increase of Tc is proportional to the increase in the average Fe-Fe distance, which allows us to conclude that the dominant cause of the Tc enhancement of amorphous Fe93Zr7 upon doping is a volume effect.
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4.
  • Alouhmy, M., et al. (författare)
  • Effects of hydrogen implantation on the magnetocaloric properties of amorphous FeZr films
  • 2021
  • Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 186
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the effects of H-implantation on the magnetic and magnetocaloric properties of amorphous FeZr films. Arrott plots reveal a second order ferromagnetic to paramagnetic phase transition for the as-grown and H-implanted films, with an increase in T-C from 160 to 200 K upon implantation. The maximum change in magnetic entropy (-Delta S-M) increases from 0.66 to 0.77J/kgK for a field change mu 0 Delta H = 1.5T, as well as the relative cooling power (RCP) values were improved from 84.5 to 108.6J/kg. This improvement was attributed to the increase in magnetization and chemical inhomogeneity induced by the implantation process. The increase in the chemical inhomogeneity was supported by the determination of the local exponent n extracted from the slope of Ln(-Delta S-M) as a function of Ln(mu 0H), which is line with the simulated depth profile of hydrogen atoms through the FeZr film.
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5.
  • Alouhmy, M., et al. (författare)
  • Random magnetic anisotropy approach in amorphous Fe88.4Zr11.6 films : Effects of hydrogen implantation
  • 2021
  • Ingår i: Journal of Non-Crystalline Solids. - 0022-3093 .- 1873-4812. ; 566
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of hydrogen implantation on the magnetic properties in amorphous Fe88.4Zr11.6Hx films with different hydrogen contents (0≤ x≤16) were investigated. The Curie temperature increases with increasing hydrogen content while the coercivity presents an important decrease upon H implantation. Based on the analysis of the approach to saturation in magnetization, the local random anisotropy constant KL was extracted. The local random anisotropy constant decreases from 1.468 MJ/m3 to 0.667 MJ/m3 when the concentration of H increases from 0 to 16%. The ferromagnetic correlation length was found to significantly increase with increasing hydrogen content. The local anisotropy was also extracted from the coercivity based on the Alben and Becker theory, which fits reasonably with that obtained using random magnetic anisotropy approach.
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6.
  • Conlon, C. S., et al. (författare)
  • Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction
  • 2019
  • Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 126:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 +/- 4 angstrom, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 angstrom. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.
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7.
  • Magnus, Fridrik, et al. (författare)
  • Giant magnetic domains in amorphous SmCo thin films
  • 2014
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:22, s. 224420-1-224420-5
  • Tidskriftsartikel (refereegranskat)abstract
    • The potential for tuning of magnetic properties and the exceptional uniformity are among the features that make amorphous magnetic materials attractive for technology. Here it is shown that the magnetization reversal in amorphous SmCo thin films takes place through the formation of giant magnetic domains, over a centimeter across. The domain structure is found to be dictated by the direction of the imprinted in-plane easy axis and the film boundaries. This is a consequence of the size of the anisotropy and the structural uniformity of the films, which also allows the movement of millimeter-long domain walls over distances of several millimeters. The results demonstrate the possibility of tailoring the magnetic domain structure in amorphous magnets over a wide range of length scales, up to centimeters. Moreover, they highlight an important consequence of the structural perfection of amorphous films.
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8.
  • Magnus, Fridrik, et al. (författare)
  • Magnetostrictive properties of amorphous SmCo thin films with imprinted anisotropy
  • 2014
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:13, s. 134414-1-134414-6
  • Tidskriftsartikel (refereegranskat)abstract
    • We examine the magnetostriction in amorphous SmCo thin films with a composition in the range 4-27 at.% Sm. The magnetostriction increases significantly with increasing Sm content but is small compared to terbium-based ferromagnetic compounds, despite the large imprinted anisotropy. The magnetostriction and anisotropy both increase approximately linearly as the temperature is reduced. The magnetoelastic energy is found to be far smaller than the anisotropy energy so the magnetoelastic atomic displacements during growth cannot be the origin of the imprinted anisotropy. The anisotropy is only slightly altered by the application of large tensile stresses, indicating that the local strain fields involved in magnetostriction are not equivalent to the global strain produced by mechanical bending.
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9.
  • Magnus, Fridrik, et al. (författare)
  • Tunable giant magnetic anisotropy in amorphous SmCo thin films
  • 2013
  • Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 102:16, s. 162402-
  • Tidskriftsartikel (refereegranskat)abstract
    • SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2-35 at.% Sm. Films with 5 at.% or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11-22 at.% Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications. 
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10.
  • Moubah, Reda, et al. (författare)
  • Anisotropic Magnetostriction and Domain Wall Motion in Sm10Co90 Amorphous Films
  • 2013
  • Ingår i: APPL PHYS EXPRESS. - 1882-0778. ; 6:5, s. 053004-
  • Tidskriftsartikel (refereegranskat)abstract
    • We show that Sm10Co90 amorphous films exhibit anisotropic magnetostriction effects when a magnetic field is applied perpendicular to the imprinted easy axis of magnetization. At low applied fields (0-100 mT), we observe strong anisotropy in the field response. Parallel to the applied field, the strain scales linearly with the applied field while the strain perpendicular to the field direction ( easy axis) is close to the detection limit. This behavior is accompanied by zigzag domain wall motion with the corners pointing along the easy axis. The origin of the anisotropic magnetostriction is discussed.
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  • Resultat 1-10 av 18
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