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Layer-resolved study of Mg atom incorporation at MgO/Ag(001) buried interface  [PDF]
T. Jaouen,S. Tricot,G. Delhaye,B. Lépine,D. Sébilleau,G. Jézéquel,P. Schieffer
Physics , 2013, DOI: 10.1103/PhysRevLett.111.027601
Abstract: By combining x-ray excited Auger electron diffraction experiments and multiple scattering calculations we reveal a layer-resolved shift for the Mg KL23L23 Auger transition in MgO ultrathin films (4-6 \AA) on Ag(001). This resolution is exploited to demonstrate the possibility to control Mg atoms incorporation at the MgO/Ag(001) interface by exposing the MgO films to a Mg flux. A substantial reduction of the MgO/Ag(001) work function is observed during the exposition phase and reflects, both band-offset variations at the interface and band bending effects in the oxide film.
Patterned nanostructure in AgCo/Pt/MgO(001) thin film  [PDF]
Zhi-Rong Liu,Huajian Gao,L. Q. Chen,Kyeongjae Cho
Physics , 2002, DOI: 10.1103/PhysRevB.68.035429
Abstract: The formation of patterned nanostructure in AgCo/Pt/MgO(001) thin film is simulated by a technique of combining molecular dynamics and phase-field theory. The dislocation (strain) network existing in Pt/MgO is used as a template whose pattern is transferred to AgCo phase in spinodal decomposition, resulting in regular arrays of Co islands that are attracted by the dislocations. The influence of various factors, such as component concentration and film thickness, is studied. It is found that the spinodal decomposition of AgCo in this system is mainly characterized by a competition between a surface-directed layer structure and the strain-induced patterned structure, where the patterned Ag-Co structure only dominates in a small range near the interface (less than 10 atomic layers). However, if the interlayer diffusion can be minimized by controlling film growth conditions, it is shown that the patterned structure can be formed throughout the entire film.
X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO (100)  [PDF]
W. Q. Liu,M. Y. Song,N. J. Maltby,S. P. Li,J. G. Lin,M. G. Samant,S. S. P. Parkin,P. Bencok,Paul Steadman,Alexey Dobrynin,Y. B. Xu,R. Zhang
Physics , 2015, DOI: 10.1063/1.4916296
Abstract: The spin and orbital magnetic moments of the Fe3O4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism (XMCD). The ultrathin film retains a rather large total magnetic moment, i.e. (2.7+-0.15) uB/f.u., which is ~ 70% of that for the bulk-like Fe3O4. A significant unquenched orbital moment up to (0.54+-0.05) uB/f.u. was observed, which could come from the symmetry breaking at the Fe3O4/MgO interface. Such sizable orbital moment will add capacities to the Fe3O4-based spintronics devices in the magnetization reversal by the electric field.
TiO2 as an electrostatic template for epitaxial growth of EuO on MgO(001) by reactive molecular beam epitaxy  [PDF]
A. G. Swartz,Jared J. I. Wong,I. V. Pinchuk,R. K. Kawakami
Physics , 2012, DOI: 10.1063/1.4704685
Abstract: We investigate the initial growth modes and the role of interfacial electrostatic interactions of EuO epitaxy on MgO(001) by reactive molecular beam epitaxy. A TiO2 interfacial layer is employed to produce high quality epitaxial growth of EuO on MgO(001) with a 45{\deg} in plane rotation. For comparison, direct deposition of EuO on MgO, without the TiO2 layer shows a much slower time evolution in producing a single crystal film. Conceptual arguments of electrostatic repulsion of like-ions are introduced to explain the increased EuO quality at the interface with the TiO2 layer. It is shown that ultrathin EuO films in the monolayer regime can be produced on the TiO2 surface by substrate-supplied oxidation and that such films have bulk-like magnetic properties.
Structure of Quasicrystalline and Crystalline Ultrathin Film Ba-Ti-O  [PDF]
Eric Cockayne,Marek Mihalkovic,Christopher L. Henley
Physics , 2015,
Abstract: We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structure is a simple decoration of three types of tiles: square, triangle and 30 degree rhombus, with edge lengths 6.85 Angstroms, joined edge-to-edge in a quasicrystalline pattern; observed crystalline Ba-Ti-O structures are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.
The influence of oxygen and hydrogen adsorption on the magnetic structure of the ultrathin iron film on the Ir(001) surface  [PDF]
Frantisek Maca,Josef Kudrnovsky,Vaclav Drchal,Josef Redinger
Physics , 2013,
Abstract: We present a detailed ab initio study of the electronic structure and magnetic order of an Fe monolayer on the Ir(001) surface covered by adsorbed oxygen and hydrogen. The results are compared to the clean Fe/Ir(001) system, where recent intensive studies indicated a strong tendency towards an antiferromagnetic order and complex magnetic structures. The adsorption of an oxygen overlayer significantly increases interlayer distance between the Fe layer and the Ir substrate, while the effect of hydrogen is much weaker. We show that the adsorption of oxygen (and also of hydrogen) leads to a p(2$\times $1) antiferromagnetic order of the Fe moments, which is also supported by an investigation based on a disordered local moment state. Simulated scanning tunneling images using the simple Tersoff-Hamann model hint that the proposed p(2$\times $1) antiferromagnetic order could be detected even by non-magnetic tips.
X-ray interference effects on the determination of structural data in ultrathin La2/3Sr1/3MnO3 epitaxial thin films  [PDF]
D. Pesquera,R. Bachelet,G. Herranz,J. Fontcuberta,X. Marti,V. Holy
Physics , 2013, DOI: 10.1063/1.3663574
Abstract: We analyze X-ray diffraction data used to extract cell parameters of ultrathin films on closely matching substrates. We focus on epitaxial La2/3Sr1/3MnO3 films grown on (001) SrTiO3 single crystalline substrates. It will be shown that, due to extremely high structural similarity of film and substrate, data analysis must explicitly consider the distinct phase of the diffracted waves by substrate and films to extract reliable unit cell parameters. The implications of this finding for the understanding of strain effects in ultrathin films and interfaces will be underlined
Surface phonons of NiO(001) ultrathin films grown pseudomorphically on Ag(001)  [PDF]
K. L. Kostov,S. Polzin,F. O. Schumann,W. Widdra
Physics , 2015,
Abstract: For a ultrathin NiO(001) film of 4 monolayers (ML) thickness grown on Ag(001), the vibrational properties have been determined by high-resolution electron energy loss spectroscopy (HREELS). For the well-ordered pseudomorphically grown film, nine phonon modes have been identified and their dispersions have been revealed along the Gamma-X high-symmetry direction. The comparison with phonon data for a 25 ML thick NiO(001) film shows that the NiO (001) phonon properties are already fully developed at 4 ML. Significant differences are found for the surface-localized phonon S6 which has an increased dispersion for the ultrathin film. The dipole-active Fuchs-Kliewer phonon-polariton exhibits a narrower lineshape than the mode found for a single-crystal surface, which might hint to a reduced antiferromagnetic coupling in the ultrathin film.
Voltage-assisted Magnetization Switching in Ultrathin Fe80Co20 Alloy Layers  [PDF]
Yoichi Shiota,Takuto Maruyama,Takayuki Nozaki,Teruya Shinjo,Masashi Shiraishi,Yoshishige Suzuki
Physics , 2009, DOI: 10.1143/APEX.2.063001
Abstract: Growing demands for the voltage-driven spintronic applications with ultralow-power consumption have led to new interest in exploring the voltage-induced magnetization switching in ferromagnetic metals. In this study, we observed a large perpendicular magnetic anisotropy change in Au(001) / ultrathin Fe80Co20(001) / MgO(001) / Polyimide / ITO junctions, and succeeded in realizing a clear switching of magnetic easy axis between in-plane and perpendicular directions. Furthermore, employing a perpendicularly magnetized film, voltage-induced magnetization switching in the perpendicular direction under the assistance of magnetic fields was demonstrated. These pioneering results may open a new window of electric-field controlled spintronics devices.
Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)  [PDF]
Tobias Schemme,Olga Kuschel,Florian Bertram,Karsten Kuepper,Joachim Wollsch?ger
Physics , 2015,
Abstract: Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe3O4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by x-ray photo electron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach x-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34nm) while the Fe3O4 films relax continuously up to the thickness of 50nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe3O4-NiO interface roughens continuously up to 1nm root-mean-square roughness with increasing NiO film thickness while the Fe3O4 surface is very smooth independent on the Fe3O4 film thickness. Finally, the Fe3O4-NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO-MgO interface is expanded.
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