| 1. |
- Poulopoulos, P., et al.
(författare)
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Induced spin-polarization of EuS at room temperature in Ni/EuS multilayers
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:11, s. 112411-
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Tidskriftsartikel (refereegranskat)abstract
- Ni/EuS multilayers with excellent multilayer sequencing are deposited via e-beam evaporation on the native oxide of Si(100) wafers at 4 x 10(-9) millibars. The samples have very small surface and interface roughness and show sharp interfaces. Ni layers are nanocrystalline 4-8 nm thick and EuS layers are 2-4 nm thick and are either amorphous or nanocrystalline. Unlike for Co/EuS multilayers, all Eu ions are in divalent (ferromagnetic) state. We show a direct antiferromagnetic coupling between EuS and Ni layers. At room temperature, the EuS layers are spin-polarized due to the proximity of Ni. Therefore, Ni/EuS is a candidate for room-temperature spintronics applications. (C) 2014 AIP Publishing LLC.
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| 2. |
- Majewski, P., et al.
(författare)
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Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:13
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the magnetic moment of the W ion in the ferrimagnetic double perovskites Sr2CrWO6 and Ca2CrWO6 by x-ray magnetic circular dichroism at the W L-2,L-3 edges. In both compounds a finite negative spin and positive orbital magnetic moment was detected. The experimental results are in good agreement with band-structure calculations for (Sr/Ca)(2)CrWO6 using the full-potential linear muffin-tin orbital method. It is remarkable that the magnetic ordering temperature, T-C, is correlated with the magnetic moment at the nonmagnetic W atom.
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| 3. |
- Pappas, S. D., et al.
(författare)
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Direct evidence for significant spin-polarization of EuS in Co/EuS multilayers at room temperature
- 2013
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3, s. 1333-
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Tidskriftsartikel (refereegranskat)abstract
- The new era of spintronics promises the development of nanodevices, where the electron spin will be used to store information and charge currents will be replaced by spin currents. For this, ferromagnetic semiconductors at room temperature are needed. We report on significant room-temperature spin polarization of EuS in Co/EuS multilayers recorded by x-ray magnetic circular dichroism (XMCD). The films were found to contain a mixture of divalent and trivalent europium, but only Eu++ is responsible for the ferromagnetic behavior of EuS. The magnetic XMCD signal of Eu at room temperature could unambiguously be assigned to magnetic ordering of EuS and was found to be only one order of magnitude smaller than that at 2.5 K. The room temperature magnetic moment of EuS is as large as the one of bulk ferromagnetic Ni. Our findings pave the path for fabrication of room-temperature spintronic devices using spin polarized EuS layers.
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| 4. |
- Vlachos, A., et al.
(författare)
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Magnetic Properties of Textured CoPd Nanocrystalline Thin Films
- 2012
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 12:8, s. 6240-6247
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Tidskriftsartikel (refereegranskat)abstract
- CoPd is an important nanomaterial for magnetic and magneto-optic storage of information. In this work, CoPd alloyed thin films are grown via radio frequency magnetron sputtering on silicon, glass and polyimide substrates in a vacuum chamber with base pressure of 5 x 10(-8) mbar. The films are nanocrystalline with grain size between 4 and 80 nm. The magnetic properties of thoroughly textured CoPd alloyed thin films are compared to random polycrystalline ones. Magnetization hysteresis loops recorded under fields up to 12 kOe via a home-made magneto-optic Kerr-effect magnetometer reveal strong tendency for perpendicular magnetic anisotropy for the textured film. This anisotropy leads to the formation of well-defined stripe or labyrinthine ferromagnetic domains with the local spins oriented perpendicular to the film plane. The domain patterns and the hysteresis loops are simulated with micromagnetic calculations. Finally, an induced magnetic moment of 0.44 mu B/atom is measured for Pd via X-ray magnetic circular dichroism and it is separated into spin and orbital magnetic moment contributions.
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| 5. |
- Winkler, A., et al.
(författare)
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Magnetism in Re-based ferrimagnetic double perovskites
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11, s. 073047-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A(2)FeReO(6) (A = Ba, Sr, Ca) by x-ray magnetic circular dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds, an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr(2)ScReO(6) proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.
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| 6. |
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| 7. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
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Violation of Hund’s third rule in structurally disordered ferromagnets
- 2011
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 84:2, s. 024411-
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Tidskriftsartikel (refereegranskat)abstract
- Violation of Hund’s third rule caused by structural disorder is observed for the induced magnetic moment of Zr, using X-ray magnetic circular dischroism. The induced spin and orbital magnetic moments are anti-parallel in the crystalline state, but parallel in an amorphous state of the investi- gated Co- and Fe-based materials. First principles calculations are used to provide physical insight into the dependency of the spin-orbit coupling on the interatomic distance and coordination number.
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| 8. |
- Krockenberger, Y., et al.
(författare)
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Sr2CrOsO6 : End point of a spin-polarized metal-insulator transition by 5d band filling
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:2, s. 020404-
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Tidskriftsartikel (refereegranskat)abstract
- In the search for new spintronic materials with high spin polarization at room temperature, we have synthesized an osmium-based double perovskite with a Curie temperature of 725 K. Our combined experimental results confirm the existence of a sizable induced magnetic moment at the Os site, supported by band-structure calculations, in agreement with a proposed kinetic-energy-driven mechanism of ferrimagnetism in these compounds. The intriguing property of Sr2 CrOs O6 is that it is at the end point of a metal-insulator transition due to 5d band filling and at the same time ferrimagnetism and high-spin polarization are preserved.
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| 9. |
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| 10. |
- Tao, Quanzheng, et al.
(författare)
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Rare-earth (RE) nanolaminates Mo4RE4Al7C3 featuring ferromagnetism and mixed-valence states
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
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Tidskriftsartikel (refereegranskat)abstract
- Rare-earth-based (RE) nanolaminates have attracted attention recently because of their complicated magnetism and their potential as precursors for strongly correlated two-dimensional materials. In this work, we synthesized a class of nanolaminates with a Mo4RE4Al7C3 chemistry, where RE = Ce or Pr. Powder samples of both phases were characterized with respect to structure and composition. Single crystals of Mo4Ce4Al7C3 were used for magnetization measurements. The crystal structure was investigated by means of x-ray diffraction and scanning transmission electron microscopy. Magnetization analysis reveals a ferromagnetic ground state with a Curie temperature of similar to 10.5 K. X-ray absorption near-edge structure provides experimental evidence that Ce is in a mixed-valence state. X-ray magnetic circular dichroism shows that only the Ce atoms with 4f(1) configuration occupying one of the two possible sites are ferromagnetically coupled, with a saturation moment of similar to 1.2 mu(B) per atom. We thus classify Mo4Ce4Al7C3 as a ferromagnetic, mixed-valence compound.
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| 11. |
- Badr, Hussein O., et al.
(författare)
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Bottom-up, scalable synthesis of anatase nanofilament-based two-dimensional titanium carbo-oxide flakes
- 2022
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Ingår i: Materials Today. - : ELSEVIER SCI LTD. - 1369-7021 .- 1873-4103. ; 54
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) materials offer advantages that their 3D counterparts do not. The conventional method for the bulk synthesis of 2D materials has predominantly been through etching layered solids. Herein, we convert - through a bottom-up approach - 10 binary and ternary titanium carbides, nitrides, borides, phosphides, and silicides into 2D flakes by immersing them in a tetramethylammonium hydroxide solution at temperatures in the 25-85 degrees C range. Based on X-ray diffraction, density functional theory, X-ray photoelectron, electron energy loss, Raman, X-ray absorption near edge structure spectroscopies, transmission and scanning electron microscope images and selected area diffraction, we conclude that the resulting flakes are carbon containing anatase-based layers that are, in turn, comprised of approximate to 6 x 10 angstrom(2) nanofilaments in cross-section some of which are few microns long. Electrodes made from some of these films performed well in lithium-ion and lithium-sulphur systems. These materials also reduce the viability of cancer cells thus showing potential in biomedical applications. Synthesizing 2D materials, at near ambient conditions, with non-layered, inexpensive, green precursors (e.g., TiC) is paradigm shifting and will undoubtedly open new and exciting avenues of research and applications.
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| 12. |
- Lumetzberger, Julia, et al.
(författare)
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Signatures of room-temperature magnetic glassiness in zinc ferrite epitaxial thin films
- 2023
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 107:14
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Tidskriftsartikel (refereegranskat)abstract
- Zinc ferrite (ZnFe2O4) epitaxial thin films were grown by reactive magnetron sputtering on MgAl2O4 and Al2O3 substrates varying a range of preparation parameters. The resulting structural and magnetic properties were investigated using a range of experimental techniques confirming epitaxial growth of ZnFe2O4 with the nominal stoichiometric composition and long-range magnetic order at and above room temperature. The main preparation parameter influencing the temperature Tf of the bifurcation between M(T) curves under field-cooled and zero-field-cooled conditions was found to be the growth rate of the films, while growth temperature or the Ar:O2 ratio did not systematically influence Tf. Furthermore Tf was found to be systematically higher for MgAl2O4 as substrate and Tf extends to above room temperature. While in some samples Tf seems to be more likely correlated with superparamagnetism, the highest Tf occurs in ZnFe2O4 epitaxial films where experimental signatures of magnetic glassiness can be found. Element-selective x-ray magnetic circular dichroism measure-ments aim at associating the magnetic glassiness with the occurrence of a different valence state and lattice site incorporation of Fe pointing to a complex interplay of various competing magnetic interactions in ZnFe2O4.
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| 13. |
- Magnani, N., et al.
(författare)
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Magnetic Polarization of the Americium J=0 Ground State in AmFe2
- 2015
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:9
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Tidskriftsartikel (refereegranskat)abstract
- Trivalent americium has a nonmagnetic (J = 0) ground state arising from the cancellation of the orbital and spin moments. However, magnetism can be induced by a large molecular field if Am3+ is embedded in a ferromagnetic matrix. Using the technique of x-ray magnetic circular dichroism, we show that this is the case in AmFe2. Since < J(z)> = 0, the spin component is exactly twice as large as the orbital one, the total Am moment is opposite to that of Fe, and the magnetic dipole operator < T-z > can be determined directly; we discuss the progression of the latter across the actinide series.
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| 14. |
- Wilhelm, F., et al.
(författare)
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X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:2, s. 024424-
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Tidskriftsartikel (refereegranskat)abstract
- The actinide cubic Laves compounds NpAl2, NpOs2, NpFe2, and PuFe2 have been examined by x-ray magnetic circular dichroism (XMCD) at the actinide M-4,M-5 absorption edges and Os L-2,L-3 absorption edges. They have the interesting feature that the An-An spacing is close to the so-called Hill limit so that substantial hybridization between the 5f states on neighboring atoms is expected to occur. The XMCD experiments performed at the M-4,M-5 absorption edges of Np and Pu allow us to determine the spectroscopic branching ratio, which gives information on the coupling scheme in these materials. In all materials, the intermediate coupling scheme is found appropriate. Comparison with the magnetization data for NpOs2 and neutron results for PuFe2 allows a determination of the individual orbital and spin magnetic moments and the magnetic-dipole contribution m(md). The resulting orbital and spin magnetic moments are in good agreement with earlier values determined by neutron diffraction, and the values of m(md) are non-negligible, and close to those predicted for intermediate coupling. There is a comparatively large induced moment on the Os atom in NpOs2 such that the Os contribution to the total moment per formula unit is similar to 30% of the total. The spin and orbital moments at the Os site are parallel, in contrast to the antiparallel configuration that we find for Os impurities in a 3d ferromagnetic transition-metal alloy. Calculations using the LDA + U technique are reported. The ab initio computed XMCD spectra show good agreement with experimental spectra for small values (0-1 eV) of the Hubbard U parameter, which demonstrates that the 5f electrons in these compounds are relatively delocalized. The calculations confirm the sign and magnitude of the experimentally determined induced magnetic moments on the Os site in NpOs2. A posteriori, by comparison of the theoretical and measured XMCD spectra for a given material, we can determine the most appropriate LSDA + U variant and, more importantly, the applicable value of the Hubbard U parameter.
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