In epitaxial heterostructures combining strongly correlated manganese oxides with antiferromagnetic-insulator or half-metallic character, a large interfacial moment is found and used to produce a spin-filter-like behavior in all-manganite tunnel junctions. The results suggest that after playing a key role in exchange-bias for spin-valves, uncompensated moments at engineered antiferromagnetic interfaces represent a novel route for generating highly spin-polarized currents with antiferromagnets.

A current drawback of spintronics is the large power that is usually required for magnetic writing, in contrast with nanoelectronics, which relies on "zero-current," gate-controlled operations. Efforts have been made to control the spin-relaxation rate, the Curie temperature, or the magnetic anisotropy with a gate voltage, but these effects are usually small and volatile. We used ferroelectric tunnel junctions with ferromagnetic electrodes to demonstrate local, large, and nonvolatile control of carrier spin polarization by electrically switching ferroelectric polarization. Our results represent a giant type of interfacial magnetoelectric coupling and suggest a low-power approach for spin-based information control.

Developments in instrumentation are essential to open new fields of science. This clearly applies to electron microscopy, where recent progress in all hardware components and in digitally assisted data acquisition and processing has radically extended the domains of application. The demonstrated breakthroughs in electron optics, such as the successful design and practical realization and the use of correctors, filters and monochromators, and the permanent progress in detector efficiency have pushed forward the performance limits, in terms of spatial resolution in imaging, as well as for energy resolution in electron energy-loss spectroscopy (EELS) and for sensitivity to the identification of single atoms. As a consequence, the objects of the nanoworld, of natural or artificial origin, can now be explored at the ultimate atomic level. The improved energy resolution in EELS, which now encompasses the near-IR/visible/UV spectral domain, also broadens the range of available information, thus providing a powerful tool for the development of nanometre-level photonics. Furthermore, spherical aberration correctors offer an enlarged gap in the objective lens to accommodate nanolaboratory-type devices, while maintaining angström-level resolution for general characterization of the nano-object under study.

Electron transfer between the electrodes in a Magnetic Tunnel Junction (MTJ) is spin-dependent and directly related to the relative orientation of the magnetization of the two ferromagnetic layers on each side of the insulator barrier. TMR (tunnel magneto-resistance) values of several hundreds of % have been measured for the present MTJ generation, however well below the theoretical expectations. Higher TMR values measured on the epitaxial Co(Fe)/MgO/Co(Fe) system, reflect the position of the Fermi level which lies in the d-band where the electrons with Δ5 symmetry are only partly spin-polarized. Bridging experimental results with theoretical modelling requires a deeper investigation of the hybridization with the d electrons of transition atoms at the interfaces. In-situ XPS measurements on the Fe/MgO [1] have revealed that the hybridization between the Fe(d) and O(p) electrons seems to be rather small. However, we have no information about the CoFe/MgO system except a recent work (CoFeB [2]).

Y2O3 thin films are deposited by ion beam sputtering on Si, SrTiO3 and MgO substrates. In order to obtain a better knowledge on the phase transition mechanisms in yttrium oxide, the effects of ion implantation have been studied as a function of the initial microstructure of thin films. The different microstructures for the as-deposited and implanted samples have been studied and characterized by means of X ray diffraction, High Resolution Transmission Electron Microscopy and Electron Energy Loss Spectroscopy and are compared to the cubic-C and monoclinic-B phase of Y2O3. The experimental results show clearly the presence of non-equilibrium phases in the implanted and non-implanted thin films. A particular attention is paid to the understanding of the relationship between the oxygen vacancy network organization, the stoichiometry and the formation mechanisms of these crystallographic phases.

Some interfaces in semiconductors or insulators structurally cause a valence mismatch, which leads to a two-dimensional space charge that must be balanced by localised or mobile charge carriers. Screening by mobile electrons presents a lot of theoretical as well as practical interests. However it is extremely rare, so that we are aware of only one case, on which we focus here: the (0 0 1) interface between LaAlO3 and TiO2-terminated SrTiO3. Theoretically, this interface between two insulators is positively charged. Electron conductivity is observed in this system, but whether it is associated with the interface screening or an extrinsic unintended doping is not yet settled. Here, we use the literature and our own numerical and practical experiments to discuss the physics of this system.

A half-metal has been defined as a material with propagating electron states at the Fermi energy only for one of the two possible spin projections, and as such has been promoted as an interesting research direction for spin electronics. This review details recent advances on manganite thin film research within the field of spintronics, before presenting the structural, electronic and spin-polarized solid-state tunnelling transport studies that we have performed on heterostructures involving La(2/3)Sr(1/3)MnO(3) thin films separated by SrTiO(3) barriers. These experiments demonstrate that, with a polarization of spin [Formula: see text] electrons at the Fermi level that can reach 99%, the La(2/3)Sr(1/3)MnO(3)/SrTiO(3) interface for all practical purposes exhibits half-metallic behaviour. We offer insight into the electronic structure of the interface, including the electronic symmetry of any remaining spin [Formula: see text] states at the Fermi level. Finally, we present experiments that use the experimental half-metallic property of manganites as tools to reveal novel features of spintronics.

The authors have observed stable, reversible two-resistance states with substantial tunneling magnetoresistances of opposite signs in La0.7Sr0.3MnO3∕SrTiO3∕Co1−xCrx junctions. Electron energy loss spectroscopy studies reveal the segregation and oxidation of electrochemically reactive chromium at that interface, resulting in oxygen vacancies in the oxide barrier. Bias-induced switching between the two junction states is argued to reflect the incidence of these barrier defects at and near the electrically unstable SrTiO3∕Co1−xCrx interface. This affirms bias crafting as an additional lever in spintronic research across semiconducting spacers.

Y2O3 thin films deposited on (001)-MgO substrate have been investigated by high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy. Digital processing of the HRTEM images reveals the presence of grains with a crystallographic structure different from that of the rest of the film (Ia3). The spectrum imaging technique has been applied in vicinity of the Y2O3/MgO interface to get a better knowledge of the phases nucleated on the substrate surface. Fine structures of the O K-edge have been studied in detail; actually two kinds of spectra have been detected in the yttrium oxide thin film. These spectra have been compared to self-consistent full multiple scattering calculations (SC-FMS). One family of spectra has then been associated to the well-known Ia3 structure. The other family of spectra has been compared to calculations performed for the other known structures (such as hexagonal or monoclinic) of Y2O3 with a little success. We have finally compared these spectra to calculations performed with a particular atomic arrangement (octahedral) of Y and O atoms, which leads to a good match between experimental and calculated spectra. Our results emphasize the benefit of coupling several techniques such as HRTEM, EELS and SC-FMS for the determination of structures at the nanometric scale.

The exact perovskite structure has simple cubic symmetry and composition ABO(3), where A is a relatively large cation and B a smaller one. The choices of A and B cations, and the substitutions possible on either site, generate a large variety of materials sharing the same base, with relatively small distortions of the size and shape of the cube. In addition, these oxides often allow oxygen non- stoichiometry with or without order to the amount of several percent. They form a vast set of technologically important materials due to their conducting, insulating, ferroelectric, magnetic, superconducting, etc., properties. Heteroepitaxy of perovskite oxides allows one to construct atomically sharp interfaces between these materials and therefore to envisage a set of useful heterojunctions. The epitaxy has side effects that may also prove useful: ( 1) it forces a chemical neighbouring that would not occur naturally, creating a two-dimensional third material, and ( 2) it imposes a lateral strain. Both of these effects allow one to explore novel, sometimes unforeseen, properties with a strong two-dimensional character. This paper first reviews some of the knowledge that has been accumulated on {100} surfaces and interfaces of perovskites, with an emphasis on properties that could be used in future all-oxide microelectronics. It then exposes the case of the interface between the half-metal La-2/3Sr(1/3)MnO(3) and the insulator SrTiO3, which plays a key role in the magnetoresistance of magnetic tunnel junctions. It particularly presents thorough electron energy loss spectroscopy measurements that uncover the atomic scale structural and electronic properties of these objects.

There has been a renewed interest in zinc oxide in the materials science community after it was shown to be ferromagnetic when doped with cobalt. However, it has remained difficult to tell whether the origin of the phenomenon was intrinsic or due to secondary phases. Here, we examine with analytical transmission electron microscopy the distribution of cobalt in a thin film of ferromagnetic Al-doped Zn0.7Co0.3O that we have grown by pulsed laser deposition on alumina. We show that precipitation of a secondary phase does occur, but that it concerns less than 10% of the cobalt atoms. The precipitates appear to be made of hexagonal metallic Co, and their average diameter is 4 mu. Their magnetism could be the reason for the low measured Curie temperature of the sample (50 K). On the other hand, the overall measured magnetization of 0.7 mu(B) per cobalt. atom suggests that the Co atoms in solution are at the origin of most of the signal.

The oxygen octahedral cage in perovskites is often occupied by a transition metal cation. The electron occupancy of the valence levels of that cation strongly depends on the electrostatic charge of its surroundings: charge of other cations and presence of oxygen vacancies. The band structure itself also depends on the distortions of the site (Jahn-Teller effect). The density of states available for excited electrons at such a site is thus particularly sensitive to the proximity of an interface. EELS L-edges of 3d transition metals correspond to excitations of electrons from the 2p core levels to a superposition of empty 4s and 3d levels. Their shapes can in some cases be analysed directly in terms of local composition and structure. The case of Ti in SrTiO3 is quite exemplary in this respect as its valency being 4+, its 4s and 3d-bands are completely empty. Moreover, its valency can change to 3+ at interfaces or in the presence of oxygen vacancies, and Muller and co-workers have shown that such variations appear indeed very clearly in the EELS signal [1]. Here, we analyse the behaviour of the transition metals Mn and Ti L signals at the (001) interface between SrTiO3 (STO) and La2/3Sr1/3MnO3 (LSMO) [2]. The changes occuring at this interface, concern only the Mn ions in LSMO, while the edges remain unmodified for the Ti ions on STO’s side, and they can be correlated to variations in magnetic coordination. Preliminary measurements concerning Ti edges at the interface of STO with perovskites having cations of different valences, such as LaAlO3 and La05Sr0.5TiO3 [3], will also be reported.

In CoO-Ag granular films with small CoO contents, we have observed ultrafine Co particles inside or on the surface of the CoO particles. After field cooling under the external magnetic field of 50 kOe, a sustained magnetization (or vertical) shift and exchange field shift were observed. The magnetization shift and the exchange field shift increased as the cooling field is increased and temperature decreased, in correlation to each other.

Electron energy loss spectroscopy (EELS), high resolution transmission electron microscopy (HRTEM), and electron diffraction were used to investigate Y2O3 thin films epitaxially grown on (001) MgO substrate. In the vicinity of the film/substrate interface, HRTEM experiments evidenced the presence of grains with various crystallographic structures most of them crystallizing in the well-known Ia3 cubic phase. Some other grains, nanometric in size, and only observed in the vicinity of the film/substrate interface, have a different and unknown crystallographic structure. EELS spectra have been acquired close to the Y2O3/MgO interface, to get a better knowledge of the phases nucleated close to the substrate surface. Spectra exhibiting different fine structures have been recorded and compared to multiple scattering calculations. The Ia3 phase has been detected as constituting the main component of the Y2O3 thin film in agreement with previous observations. It is found that calculations performed in a real space self-consistent full multiple scattering scheme (SC-FMS) and experiments are in pretty good agreement even for small cluster sizes. The second family of spectra has also been compared to calculations performed for monoclinic C2/m yttrium oxide, with a little success. Another approach considering a local oxygen neighboring close to a distorted rock-salt-like structure led to a good match between experimental and calculated spectra. Our results emphasize how powerful is the combination of spectroscopic measurements at nanometer scale, as feasible with EELS and modern microscopes, with ab initio calculations for structure determination at such small scale lengths.

(Cu,Mg) alloys are internally oxidized at different oxygen chemical potential at 900°C. Oxidation scale microstructure is studied by SEM and TEM. MgO forms as large magnesia agglomerates without any special orientation relationship and isolated cubo-octahedral topotaxial MgO precipitates, the shape of which varies with decreasing oxygen activity from octahedral to cubic. The interfaces of the cubo-octahedral precipitates are studied in detail by CTEM, HREM and EELS. At the highest oxygen activity, important rigid-body contraction/expansion across the interface is found together with a strong modification in the interfacial electronic structure (compared to the adjacent bulk phases) indicating important hybridization of O 2 p and Cu 3 d states. Both suggest oxide bonding. At lower oxygen activity, interfaces show increasing structural disorder in the copper phase and microfaceting or terracing of the interfacial plane; the intensity of interfacial ELNES features associated to the O 2 p and Cu 3 d hybridization diminishes and finally disappears with decreasing oxygen activity. Changes with oxygen chemical potential in precipitate morphology, interface atomic and electronic structure are explained by Gibbs’ adsorption/desorption of excess oxygen to the interface. Adsorption isotherms are modeled for various configurations and compared to the experimental results.

Nanostructured granular solid consisting of antiferromagnetic CoO particles embedded in a metallic medium (Ag) has been investigated by both transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) on a multiple scale. Quantitative composition determination was carried out by energy dispersive X-ray spectroscopy (EDXS) for Ag and Co, and by EELS for oxygen and Co quantification. Because of the complex morphology of the indicated CoO–Ag granular system, only a detailed analysis of the spatial variation of the EELS signals can provide information on the particle size and distribution. A mean size of 5 nm for CoO particles has been evaluated. The oxidation state of Co has also been studied using fine structures on EELS spectra. CoO phase is clearly identified as the oxide but appears mixed with small metallic Co area.

We use High Resolution Electron Microscopy together with Electron Energy Loss Spectroscopy to analyze the crystallography and the chemical configuration of a Co/SrTiO3 interface in a Co/SrTiO3/La2/3Sr1/3MnO3 magnetic tunnel junction.

Journal Article Implementing Spectral Deconvolution into the Spectrum-Imaging Mode : A New Step Towards Combined High Spatial and Energy-Resolution EELS Get access A Gloter, A Gloter Search for other works by this author on: Oxford Academic Google Scholar A Douiri, A Douiri Search for other works by this author on: Oxford Academic Google Scholar M Tencé, M Tencé Search for other works by this author on: Oxford Academic Google Scholar D Imhoff, D Imhoff Search for other works by this author on: Oxford Academic Google Scholar O Stéphan, O Stéphan Search for other works by this author on: Oxford Academic Google Scholar C Colliex C Colliex Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 9, Issue S02, 1 August 2003, Pages 108–109, https://doi.org/10.1017/S1431927603440622 Published: 06 August 2003

With a Curie point at 370 K, the half-metal (La0.7Sr0.3)MnO3 (LSMO) is one of the most interesting candidates for electronic devices based on tunnel magnetoresistance. SrTiO3 (STO) is up to now the best substrate for the epitaxy of suitable thin films of LSMO. The pseudocubic unit cell of rhombohedral LSMO has a parameter alpha(LSMO) such that (alpha(STO)-alpha(LSMO))/alpha(LSMO) = + 0.83% where alpha(STO) is the parameter of cubic STO) and an angle of 90.26degrees. As strained growth is tetragonal, relaxation implies recovery of both the pseudocubic parameter and of the original angle. In the LSMO layers that we prepare by pulsed-laser deposition, we show that these two processes are quite independent. The angular distortion is partially recovered by twinning films 25nm thick, while recovery of the parameter never occurs in the thickness range that we explored (up to 432 nm). A relaxation, however, takes place above a thickness of 100 nm, associated with a transition from two-dimensional to three-dimensional columnar growth. It is accompanied by chemical fluctuations. Our magnetic measurements exhibit Curie temperatures and magnetic moments very close to the bulk values in those layers where the crystal parameter is strained but the angle partially relaxed.