N, N'-di(1-naphthyl)-N, N'-diphenyl-(1,1'-biphenyl)-4, 4'-diamineor 2-methyl-9, 10-bis(naphthalen-2-yl)anthracene-based organic light emitting diode devices, when purposely exposed to X-rays emitted from an evaporation electron gun, reveal interesting new properties in terms of transport, magnetoconductance (MC), as well as spectral changes in their photoluminescence. For devices exhibiting MC, we report magnetic field effects with two distinct regimes. The first one, at low magnetic field, is assigned to hyperfine field effects and is slightly dependent on X-ray exposure. The second one, occurring at larger magnetic field, is due to polaron-triplet exciton coupling and depends on the irradiation dose, as well as on the organic material nature and thickness. We interpret our results in terms of extrinsic trap formation, thanks to X-rays exposure and interactions between polarons and trapped triplet excitons.

Characterization of the electromagnetic field emitted by various sources (antenna, radar, etc.) is an important issue, either for civil or defense applications. The measurement of electromagnetic field may be performed either by local probes or by thermography imaging, in particular with an infrared camera. The latter method, called electromagnetic infrared (EMIR) has been developed several years ago. We have recently successfully implemented this technique in the domain of visible light thanks to the combination of a film sensitive to either electric field (slightly conductive film) or magnetic field (insulating film with ferromagnetic particles) and a polymer coating doped with fluorescent molecules with an emission depending on temperature, indeed a thermofluorescent sensor. We present our recent results obtained imaging the microwave magnetic field emitted in the near field of a zeroth-order resonator (ZOR) antenna. The sensing film is a stack of FLEX-TOKIN magnetic absorber, already tested by EMIR infrared thermography in our group. A 20 mu m film composed of a mixture of rhodamine B (RhB) in an epoxy matrix is screen printed on the FLEX surface. RhB, in ethanol solution, has a thermofluorescence coefficient of similar to 2%/K at room temperature at its maximum of fluorescence of 595 nm. Excitation light is delivered by an array of blue 470 nm LEDs. The 4.29 GHz microwave excitation of the ZOR device is amplitude modulated at 0.1-0.5 Hz in order to cancel any thermal drift and convection of the thermofluorescence image. Low-frequency excitation modulation also allows noise cancellation via image pixel demodulation postprocessing. We present the deduced temperature mapping of the sensing film placed 2 mm above the ZOR patch antenna.

Ferromagnetic resonance has been used to investigate the effect of a Mn/Si and a Co/Mn atomic disorder on the magnetic properties and dynamic relaxation of Co2MnSi Heusler alloy. He+ ion irradiation at 150 KeV is used to induce a Co/Mn and Mn/Si swap in the initial structure of the material. While a Mn/Si disorder is found to show similar magnetic behavior as compared to the L21 order, we observe a strong impact of a Co/Mn swap on the static and dynamic properties of the alloy. These results are explained with regard to electronic band structure and damping coefficient first-principles calculations showing the modification of the minority-spin density of states at the Fermi energy and local magnetic orbital moment with Co/Mn swap.

We have investigated the atomic disorder induced by a 150 keV He+ ion irradiation in a 40 nm thick Co2MnSi Heusler alloy. Disorder parameters on each atomic site are deduced from normal and anomalous x-ray diffraction measurements with Co and Cu K alpha sources. While the film grows mainly in the L2(1) phase with inclusion of B2 grains, we observe an increase of both the Mn-Si and Co-Mn exchanges with the ion fluence. HAADF-STEM analysis demonstrates that the increase in Mn-Si disorder corresponds to a growing size of the B2 grains while the Co-Mn exchange is accounted for a D0(3) disorder type in the L2(1) matrix. These structural modifications are shown to decrease the average magnetization of the alloy, which is due to D0(3) disorder and local defects induced by irradiation.

We report on the structural investigation of FeRh thin films exhibiting a magnetic transition from an antiferromagnetic (AF) to a ferromagnetic (FM) state when heated above ≈350 K. The transition lying in a very narrow range of composition, close to the equiatomic one, and in a given chemically ordered phase (of B2-type), the composition and the growth conditions were carefully adjusted in the epitaxial growth process of the films on (001)MgO. Magnetic measurements confirmed the presence of the AF–FM transition. High-angle x-ray diffraction and electron microscopy experiments were used to characterize the FeRh structural details at different scales from statistical to highly localized information. Special attention was paid to the quality of the chemical order and the presence of defects, which condition the characteristics of the magnetic transition. Interestingly, the results reveal the presence of nanograins, displaying another structure in the equiatomic FeRh films, such grains having previously been observed in strained bulk specimens.

The thickness dependence of the static and dynamic properties of Co 2 MnSi (CMS) full Heusler was investigated. Five samples with thickness ranging from 7 to 100 nm were deposited by rf magnetron sputtering on single crystal MgO(001). X-ray diffraction and transmission electron microscopy (TEM) evidence the epitaxial growth of samples, with an epitaxial relationship MgO(001)[100]//CMS(011)[110]. Magnetic properties were studied by standard magnetometry and broadband stripline ferromagnetic resonance (FMR). We observe a four-fold magnetocrystalline anisotropy K c = 1.5 × 10 5 erg/cm 3 for thicker samples, and an increase of K c up to 2.6 × 10 5 erg/cm 3 for the thinnest sample, accompanied by an increase of saturation magnetization. We attribute this behavior to interfacial effect (strain or stoichiometry).

We report detailed structural characterization and magneto-optical Kerr magnetometry measurements at room temperature in epitaxial Co2MnSi thin films grown on MgO(001) and Cr(001) buffered MgO single crystals prepared by sputtering. While Co2MnSi/Cr//MgO(001) films display the expected cubic anisotropy, the magnetization curves obtained for Co2MnSi//MgO(001) samples exhibit a superimposed in-plane uniaxial magnetic anisotropy. The evolution of magnetization with film thickness points to a relevant interfacial Co2MnSi-buffer layer (Cr or MgO) contribution which competes with magnetic properties of bulk Co2MnSi, resulting in a drastic change in the magnetism of the whole sample. The origin of this interfacial magnetic anisotropy is discussed and correlated with our structural studies.

Effect of a shallow nitrogen implantation in the channel region of n-channel 4H-SiC Hall bar MOSFETs on their electrical properties has been characterized by Hall effect. A significant improvement of Hall mobility in normally-off devices is observed with increasing nitrogen implantation dose up to 10(13) cm(-2) with a peak Hall mobility of 42.4 cm(2).V-1.s(-1). Coulomb scattering as dominant scattering mechanism up to room temperature is demonstrated using temperature dependent MOS-Hall effect characterization.

Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10−3, and a minimum value of 3.8 × 10−3 for the Cr buffered one.

Iron/alumina multilayers have been deposited on sapphire wafers using RF magnetron sputtering. To study the interdiffusion, the multilayers were annealed in a tubular furnace under a 10−7 mbar vacuum, and the samples examined by using a combination of classical diffractometry (θ/2θ) and Grazing Incidence Scattering (GIS) for the phase determination, and Small Angle X-ray Scattering (SAXS) for the superstructure of the multilayers. In all cases, in the as-deposited state the alumina is amorphous and the iron is crystalline in the bcc phase. Thermal anneals at temperatures between 573 and 873 K give evidence for segregation to the interfaces. At higher temperatures, interdiffusion occurs, leading to the formation of different phases. The Fe-Al2O3 interdiffusion coefficient has been evaluated in the temperature range from 873 to 1273 K.

We have prepared organic spin valves based on the perylene derivative perylene-3,4,9,10-tetracarboxylate (PTCTE) with NiFe and Co ferromagnetic electrodes (with direct or off-axis sample configuration for the Co upper electrode deposition). Transmission electron miscroscopy is employed to study the stacking of the NiFe/PTCTE/Co vertical structures. Tunneling atomic force microscopy reveals that direct deposition of Co damages the PTCTE layer. Moreover, fluorescence and I-V studies of PTCTE evidence changes of the organic layer’s transport properties that are correlated with the deposition rate of PTCTE. Finally, we report up to 3% magnetoresistance at 10 mV and 5 K on a sample with an organic spacer 300 nm in thickness and an off-axis deposited cobalt counter electrode. We analyze this result in terms of spin diffusion and spin precession in PTCTE.

Ferromagnetic microstructured films of Ni80Fe20 with in-plane uniaxial anisotropy were prepared by RF magnetron sputtering and patterned into rectangles with the larger dimension parallel to the easy axis. Static properties have been measured using a magneto-optic-Kerr-effect test bench, and dynamic properties were also obtained in the microwave frequency range. Because of ferromagnetic resonance, high complex permeability is obtained, and this corresponds to losses that create local heating. So, at an appropriate frequency, a microwave incident magnetic field interacts with the film and generates heating. This heating is recorded using an infrared camera to provide magnetic field pattern images. This setup yields qualitative results and allows for magnetic field detection on a large dimension scale.

A new microwave magnetic field measurement method based on infrared emission is presented. This method uses thin patterned ferromagnetic films sputtered on polymer substrates. The incident field interacts with the film and is responsible for ferromagnetic losses that create local heating. This heating is recorded by an infrared camera, providing magnetic field pattern images and amplitude evaluation. Moreover, the tangential components of the H field can be identified thanks to the anisotropic structure of the sputtered film. The large permeability NiFe based thin films were grown using a sputtering method and complex permeability measurements have been carried out in the microwave range. Both infrared pictures and magnetic permeability measurements are presented and correlated.

In order to grow nanocrystallized soft magnetic thin films, FeCoC alloys were first deposited by reactive sputtering in Ar/C2H2 plasma. This deposition process rendered it possible to incorporate a carbon content between 0 and 30 at.% into the FeCo samples. The films were then compared to FeCoC samples obtained from a Fe65Co35/C composite target, with an adjustable amount of C slots. Layers with soft magnetic properties were achieved when increasing the C2H2 rate during the reactive deposition, whereas films deposited by sputtering of FeCo and C on the same target demonstrated a very high coercivity. Permeability spectra measurements (and published elsewhere) demonstrated that FeCoC prepared with acetylene is a very promising material for high-frequency magnetic devices.

We have used grazing incidence x-ray diffraction to observe the structural evolution during growth of sputter-deposited epitaxial Fe films on Cu(001) and Pt(001). We find that on Cu(001), Fe is fcc up to a thickness of 10-12 monolayers, whereupon bcc Fe is observed in first the Pitsch and then the Bain orientations. The fcc Fe shows some relaxation of the misfit from the Cu, as do the Pitsch orientation bcc, which is in tension, and the Bain orientation bcc, which is in compression. All three Fe variants exist in a 40 monolayer thick film. On Pt(001) the Fe grows as bcc with the Bain orientation. However, a thin (20 å) bcc Fe film is transformed to fcc Fe with cube-on-cube orientation by subsequent deposition of Pt. This behavior is consistent with intermixing of Pt into the Fe layer, which lowers the mismatch and bulk chemical energies of the fcc phase relative to that of the bcc phase.

Magnetization reversals in sputtered Co electrodes of a magnetic tunnel junction are studied using transport measurements, magneto-optic Kerr magnetometry and microscopy. Using the tunnel magneto-resistive effect as a probe for micromagnetic studies, we first evidence the existence of an unexpected domain structure in the soft Co layer. This domain structure originates from the duplication of the domain structure of the hard Co layer template into the soft layer via ferromagnetic inter-electrode coupling. A detailed analysis of the kerr microscopy images shows that all features appearing in the variation of tunnel resistance as a function of the applied field are associated to the domain phase evolution of each electrode. By tailoring the magnetic properties of the hard Co layer, we have demonstrated that the appearance of the domain duplication is driven by the magnetic anisotropy of the hard layer. Finally, a brief theoretical description of the domain duplication process allows us to extract the main parameters governing the effect.

Fe 65 Co 35 and Fe9.5Co90.5 thin films with carbon addition were deposited by reactive sputtering and investigated in terms of static and dynamic magnetic properties. The acetylene rate was adjusted in order to deposit nanocrystalline soft magnetic films, with a high saturation magnetization, a high resistivity, and a low coercivity. The transition of the crystalline structure to a nanocrystalline or amorphous arrangement—giving rise to soft magnetic properties—depended on the Fe/Co ratio and the C content. The lowest coercivity of 0.4 Oe was obtained for a Fe9.5Co90.5 film with 0.95% of C2H2, whereas a Fe65Co35 film with 0.75% of C2H2 exhibited a coercivity of 0.7 Oe. The microwave properties of the Fe65Co35 layers remained stable over this C2H2 content whereas the resonance frequency of the Fe9.5Co90.5 films decreased with the C2H2/Ar ratio. A difference in the manner that the carbon was incorporated, depending on the Fe/Co ratio, may explain the observed magnetic properties.

Organic semiconductors are very promising materials in the field of spintronic devices like spin valves (SV) because of large spin relaxation time in ¿-conjugated molecules and the advantage of rather simple and low energy consuming device fabrication techniques. Most of the studies of spin injection in organic semiconductors focused on hole transport materials and one electron transport material: the tris(8-hydroxyquinoline) aluminum (Alq3). In this article, we present our first results on SV based on a perylene derivative, PTCTE (PTCTE: tetraethyl perylene 3, 4, 9, 10-tetracarboxylate). Perylene molecules were traditionally used as electron transport materials in optoelectronic devices like OLED (organic electroluminescent diodes) and solar cells. NiFe/PTCTE/Co devices were prepared by dc sputtering for the electrodes (with direct or off axis sample configuration for the upper electrode), and vacuum sublimation for the organic layer. CPP (current perpendicular to plane) devices geometry was obtained with millimetric contact masks determining a CPP spin valve area of 1 mm × 1 mm. Up to now, our best samples have a spin valve magnetic behavior and exhibit up to 3 % MR response at low temperature for a 300 nm organic spacer layer.