uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Moubah, Reda
Publications (10 of 15) Show all publications
Conlon, C. S., Conti, G., Nemsak, S., Pálsson, G. K., Moubah, R., Kuo, C.-T. -., . . . Fadley, C. S. (2019). Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction. Journal of Applied Physics, 126(7), Article ID 075305.
Open this publication in new window or tab >>Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction
Show others...
2019 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 126, no 7, article id 075305Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-394269 (URN)10.1063/1.5089556 (DOI)000483849000004 ()
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically approved
Moubah, R., Magnus, F., Warnatz, T., Pálsson, G. K., Kapaklis, V., Ukleev, V., . . . Hjörvarsson, B. (2016). Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices. Physical Review Applied, 5(4), Article ID 044011.
Open this publication in new window or tab >>Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
Show others...
2016 (English)In: Physical Review Applied, E-ISSN 2331-7019, Vol. 5, no 4, article id 044011Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-297910 (URN)10.1103/PhysRevApplied.5.044011 (DOI)000374562100001 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-06-29 Created: 2016-06-28 Last updated: 2018-08-13Bibliographically approved
Ukleev, V., Moubah, R., Baranov, D., Gastev, S. V., Krichevtsov, B., Velichko, E., . . . Grigoriev, S. V. (2015). Imprinted Magnetic Anisotropy and Zigzag Domain Structure of Amorphous TbCo Films. Journal of Superconductivity and Novel Magnetism, 28(12), 3571-3577
Open this publication in new window or tab >>Imprinted Magnetic Anisotropy and Zigzag Domain Structure of Amorphous TbCo Films
Show others...
2015 (English)In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 28, no 12, p. 3571-3577Article in journal (Refereed) Published
Abstract [en]

We investigate the magnetic anisotropy and domain structure of amorphous Tb (x) Co(1-x) films grown in external in-plane magnetic field by high-frequency ion sputtering. Films with different thicknesses 100 and 500 nm and rare-earth element concentrations x = 12 % and x = 34 % present strong imprinted in-plane uniaxial anisotropy. Measurements of magnetic properties and domain structure imaging were performed by means of longitudinal and polar magneto-optical Kerr effect (MOKE). The coercivity fields increase by an order of magnitude for the higher Tb concentration and increase with film thickness (H (c) along the hard axis are 495, and 580 Oe, for 100 and 500 nm, with x = 34 % and 65, and 95 Oe for 100 and 500 nm with x = 12 %, respectively). Polar MOKE measurements revealed the existence of an out-of-plane magnetization component for the films with a Tb concentration of 34 % in lower fields. Large-scale domain structure of TbCo films with imprinted anisotropy was also studied as a function of applied field. Kerr imaging shows a zigzag domain structure of Tb12Co88 films, while no domains were found in Tb34Co66 samples. We also demonstrate that the zigzag angle depends on the film thickness. We suggest that domain structure in these films is determined by the interplay of imprinted and local magnetic anisotropies as well as exchange interaction.

Keywords
Hard magnetic materials, Alloys and films, Anisotropy, Domains
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-269964 (URN)10.1007/s10948-015-3172-9 (DOI)000364935100019 ()
Available from: 2015-12-19 Created: 2015-12-19 Last updated: 2017-12-01Bibliographically approved
Zamani, A., Moubah, R., Ahlberg, M., Stopfel, H., Arnalds, U., Hallén, A., . . . Jönsson, P. (2015). Magnetic properties of amorphous Fe93Zr7 films: Effect of light ion implantation. Journal of Applied Physics, 117(14), Article ID 143903.
Open this publication in new window or tab >>Magnetic properties of amorphous Fe93Zr7 films: Effect of light ion implantation
Show others...
2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 14, article id 143903Article in journal (Refereed) Published
Abstract [en]

The Curie temperature (T-c) 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)B-0.11 sample. The increase of T-c is proportional to the increase in the average Fe-Fe distance, which allows us to conclude that the dominant cause of the T-c enhancement of amorphous Fe93Zr7 upon doping is a volume effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-252143 (URN)10.1063/1.4917212 (DOI)000352967400008 ()
Funder
Swedish Research Council
Available from: 2015-05-03 Created: 2015-05-03 Last updated: 2017-12-04Bibliographically approved
Moubah, R., Magnus, F., Hjörvarsson, B. & Andersson, G. (2014). Antisymmetric magnetoresistance in SmCo5 amorphous films with imprinted in-plane magnetic anisotropy. Journal of Applied Physics, 115(5), 053911
Open this publication in new window or tab >>Antisymmetric magnetoresistance in SmCo5 amorphous films with imprinted in-plane magnetic anisotropy
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 5, p. 053911-Article in journal (Refereed) Published
Abstract [en]

We report on magnetoresistance measurements in SmCo5 amorphous films with a giant imprinted magnetic anisotropy. At low applied field parallel to the easy axis, the magnetoresistance exhibits a hysteretic, square, and antisymmetric shape. The antisymmetry in the magnetoresistance is a result of the non-uniform distribution of the magnetization direction over the sample in conjunction with the extraordinary Hall effect. Moreover, the combination of anisotropic magnetoresistance measurements and magnetic domain imaging demonstrates that the symmetry depends on the magnetization orientation with respect to the applied field.

National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-218264 (URN)10.1063/1.4864716 (DOI)000331645900058 ()
Funder
Carl Tryggers foundation Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2014-02-10 Created: 2014-02-10 Last updated: 2017-12-06Bibliographically approved
Magnus, F., Moubah, R., Arnalds, U. B., Kapaklis, V., Brunner, A., Schäfer, R., . . . Hjörvarsson, B. (2014). Giant magnetic domains in amorphous SmCo thin films. Physical Review B. Condensed Matter and Materials Physics, 89(22), 224420-1-224420-5
Open this publication in new window or tab >>Giant magnetic domains in amorphous SmCo thin films
Show others...
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 22, p. 224420-1-224420-5Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-230519 (URN)10.1103/PhysRevB.89.224420 (DOI)000339049000010 ()
Available from: 2014-09-08 Created: 2014-08-26 Last updated: 2017-12-05Bibliographically approved
Magnus, F., Moubah, R., Kapaklis, V., Andersson, G. & Hjörvarsson, B. (2014). Magnetostrictive properties of amorphous SmCo thin films with imprinted anisotropy. Physical Review B. Condensed Matter and Materials Physics, 89(13), 134414-1-134414-6, Article ID 134414.
Open this publication in new window or tab >>Magnetostrictive properties of amorphous SmCo thin films with imprinted anisotropy
Show others...
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 13, p. 134414-1-134414-6, article id 134414Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-224725 (URN)10.1103/PhysRevB.89.134414 (DOI)000334593700002 ()
Available from: 2014-05-23 Created: 2014-05-19 Last updated: 2017-12-05Bibliographically approved
Moubah, R., Ahlberg, M., Zamani, A., Olsson, A., Shi, S., Sun, Z., . . . Jönsson, P. E. (2014). Origin of the anomalous temperature dependence of coercivity in soft ferromagnets. Journal of Applied Physics, 116(5), 053906
Open this publication in new window or tab >>Origin of the anomalous temperature dependence of coercivity in soft ferromagnets
Show others...
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 5, p. 053906-Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-233598 (URN)10.1063/1.4892038 (DOI)000341178900042 ()
Available from: 2014-10-10 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
Moubah, R., Magnus, F., Hjörvarsson, B. & Andersson, G. (2014). Strain enhanced magnetic anisotropy in SmCo/BaTiO3 multiferroic heterostructures. Journal of Applied Physics, 115(5), 053905
Open this publication in new window or tab >>Strain enhanced magnetic anisotropy in SmCo/BaTiO3 multiferroic heterostructures
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 5, p. 053905-Article in journal (Refereed) Published
Abstract [en]

We report on the changes in magnetic properties of SmCo/BaTiO3 multiferroic heterostructures as the BaTiO3 substrate undergoes its structural phase transitions. The observations show that the macroscopic magnetization of the SmCo film is affected by the structural phase transitions of the BaTiO3 substrate. Kerr microscopy images show that the magnetic domains of SmCo films have a zigzag shape but their shape is not influenced by the strain transferred from the substrate during the structural phase transitions. Analysis of the magnetoelastic energy shows that the macroscopic change of the magnetization is accompanied by an enhancement of the magnetic anisotropy for the orthorhombic phase of the BaTiO3 substrate and not a change in symmetry of the anisotropy.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-218404 (URN)10.1063/1.4863819 (DOI)000331645900052 ()
Available from: 2014-02-11 Created: 2014-02-11 Last updated: 2017-12-06Bibliographically approved
Moubah, R., Magnus, F., Kapaklis, V., Hjörvarsson, B. & Andersson, G. (2013). Anisotropic Magnetostriction and Domain Wall Motion in Sm10Co90 Amorphous Films. APPL PHYS EXPRESS, 6(5), 053004
Open this publication in new window or tab >>Anisotropic Magnetostriction and Domain Wall Motion in Sm10Co90 Amorphous Films
Show others...
2013 (English)In: APPL PHYS EXPRESS, ISSN 1882-0778, Vol. 6, no 5, p. 053004-Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-202377 (URN)10.7567/APEX.6.053004 (DOI)000318778800032 ()
Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2013-06-24Bibliographically approved
Organisations

Search in DiVA

Show all publications