Lionel Presmanes

Ferromagnetic films with magnon bandgap periodic structures: Magnon crystals

A new type of photonic crystals is proposed. The new crystals have a forbidden gap in the microwave spectrum of magnetostatic spin waves, and, by analogy with photonic crystals, they are called magnon crystals. Specimens of such crystals were fabricated on the basis of yttrium iron garnet films. The surfaces of ferromagnetic films containing two-dimensional etched hole structures were studied by atomic force and magnetic force mag-netometry. The propagation of spin waves through the magnon crystals was investigated.

Measurement of Young's modulus of nanocrystalline ferrites with spinel structures by atomic force acoustic microscopy

Abstract Using Atomic Force Acoustic Microscopy, the Youngs moduli of two thin films of nanocrystalline ferrites with spinel structures have been measured as a function of the oxidation temperature on a nanoscale. There is an overall decrease of the Youngs moduli as a function of the oxidation temperature with an intermediate minimum and maximum. These measurements corroborate the existence of chemical gradients from the surface layer to the interior of the films occurring during the oxidation process in the γ-phase. They lead to stress gradients which influence the Youngs modulus and the coercivity Hc. In our measurement technique, we measure the flexural resonance frequencies of an atomic force microscope cantilever and exploit their dependence on the tip-sample contact forces, here an elastic contact described by Hertzian contact theory. The technique has been extended allowing quantitative measurements using a self-consistent calibration. Comparison to nanoindentation measurements have been made. We discuss possible nonlinear effects occurring in the contact which may lend AFAM itself to measure nonlinear parameters on a nanoscale.

p-Type conducting transparent characteristics of delafossite Mg-doped CuCrO2thin films prepared by RF-sputtering

The growth of technologically relevant compounds, Mg-doped CuCrO2 delafossite thin films, on a quartz substrate by radio-frequency sputtering is reported in this work. The deposition, performed at room temperature, leads to a nanocrystalline phase with extremely low roughness and high density. Delafossite characteristic diffraction peaks were obtained as a function of the thermal treatment under primary vacuum. The electrical conductivity was optimized until 1.6 S cm−1 with an optical transmittance of 63% in the visible range by a 600 °C annealing treatment under primary vacuum applied for 4 h. The transport properties were analyzed by Seebeck and Hall measurement, integrated spectrophotometry and optical simulation. These measurements highlighted degenerated semiconductor behavior using a hopping mechanism with a high hole concentration (1021 cm−3) and a low mobility (0.2 cm2 V−1 s−1). The direct optical bandgap of 3.3 eV has been measured according to Taucs relationship. A refractive index of 2.3 at a wavelength of 1100 nm has been determined by spectroscopic ellipsometry and confirmed by two independent modellings of the optical transmittance and reflectance spectra. All these p-type TCO optoelectronic characteristics have led to the highest Haackes figure of merit (1.5 × 10−7 Ω−1) reported so far for such delafossite materials

Measurement of mechanical properties of nanoscaled ferrites using atomic force microscopy at ultrasonic frequencies

To measure local elasticity by Atomic Force Acoustic Microscopy (AFAM), the sample placed in a commercial AFM is insonified by ultrasonic waves or the cantilever is oscillated at ultrasonic frequencies. In contact with the specimen, the cantilever-tip system vibrates out-of-plane and its resonances are measured. A quantitative model based on linear tip-sample force shows that the stiffness of the specimen can be derived from the shift of the contact resonance frequencies relative to resonance frequencies of the free cantilever. We report AFAM results with a well-known material, silicon single-crystal oriented in 〈100〉 direction, to prove the consistence of the local measurement of elasticiy. Then, in thin films of magnetite Fe3O4 and maghemite γFe2O3 with spinel structure, the influence of the deviation from the stoichiometry on the elasticity for a given grain size is determined.

Submicron MnxCo1Fe2−xO4 spinel ferrites: Cationic distribution and reactivity

Abstract Submicron Mn x Co 1 Fe 2− x O 4 spinel particles with an acicular shape were prepared from oxalic precursors. It was shown, from X-ray measurements and thermogravimetric analyses, that the valences of the cobalt and manganese ions were +II and +III respectively. Because of their small crystallite sizes (45 nm), these ferrites particles can be oxidized giving defect spinel ferrites having both Mn 3+ and Mn 4+ ions on octahedral sites. In these ferrites the enthalpy of the octahedral Mn 3+ ions oxidation was found to be close to −87 kJ mol −1 .

Magneto-optical properties of a sputtered Bi-substituted Dy–Fe garnet-ferrite/hematite bilayer

Rapid thermal annealing was performed after a Bismuth-substituted Dy iron garnet-ferrite (Bi2DyFe4GaO12) was deposited on a quartz glass substrate having a hematite underlayer, and the effect of the hematite underlayer on the magneto-optical characteristics of the garnet ferrite film was evaluated. The presence of the underlayer greatly improved the magneto-optical effect of the garnet film, but the amount of improvement depended on the hematite phase. Big improvement was obtained using underlayer phases that are easily crystallized, i.e., Fe3O4 and γ-Fe2O3 which have a spinel structure, but not with α-Fe2O3 which has a corundum structure.

Thermoelectric and Transport Properties of Delafossite CuCrO2:Mg Thin Films Prepared by RF Magnetron Sputtering

P-type Mg doped CuCrO2 thin films have been deposited on fused silica substrates by Radio-Frequency (RF) magnetron sputtering. The as-deposited CuCrO2:Mg thin films have been annealed at different temperatures (from 450 to 650 °C) under primary vacuum to obtain the delafossite phase. The annealed samples exhibit 3R delafossite structure. Electrical conductivity σ and Seebeck coefficient S of all annealed films have been measured from 40 to 220 °C. The optimized properties have been obtained for CuCrO2:Mg thin film annealed at 550 °C. At a measurement temperature of 40 °C, this sample exhibited the highest electrical conductivity of 0.60 S·cm−1 with a Seebeck coefficient of +329 µV·K−1. The calculated power factor (PF = σS²) was 6 µW·m−1·K−2 at 40 °C and due to the constant Seebeck coefficient and the increasing electrical conductivity with measurement temperature, it reached 38 µW·m−1·K−2 at 220 °C. Moreover, according to measurement of the Seebeck coefficient and electrical conductivity in temperature, we confirmed that CuCrO2:Mg exhibits hopping conduction and degenerates semiconductor behavior. Carrier concentration, Fermi level, and hole effective mass have been discussed.

Controlling garnet film composition by magnetic-field-controlled radio frequency magnetron sputtering

To find a way to control the compositional change in Bi-substituted garnet during sputtering, we studied the effects of controlling the cathode magnetic field. The magnetic-field-controlled rf magnetron sputtering method that we developed can create a garnet film whose composition is the same as that of the sputtering target. When we deposited a film of Bi-substituted Dy iron garnet–ferrite (Bi2DyFe4GaO12) by this method, there was no compositional change between the target and the film even after a long sputtering process. Therefore, this sputtering method is effective at suppressing compositional change during the film formation process.

Magneto-optical properties of a sputtered Bi-substituted Dy iron garnet-ferrite/spinel-ferrite bilayer

Abstract Bi-substituted Dy iron garnet-ferrites, Bi 2 DyFe 4 GaO 12 , were prepared by RF magnetron sputtering on a spinel-ferrite underlayer on a quartz glass substrate. This study investigated the effect of the spinel underlayer, a mixed crystal of Fe 3 O 4 and γ-Fe 2 O 3 , on improving the magneto-optical properties. It was found that the presence of the spinel-ferrite underlayer increased the Faraday effect, compared to that of a garnet layer with no underlayer, for which the Faraday effect was almost non-existent. It is concluded that the high-temperature-treated spinel-ferrite underlayer enhanced the magneto-optical characteristics. This bilayer structure is therefore promising for magneto-optical recording media.

Integration of P-CuO Thin Sputtered Layers onto Microsensor Platforms for Gas Sensing

P-type semiconducting copper oxide (CuO) thin films deposited by radio-frequency (RF) sputtering were integrated onto microsensors using classical photolithography technologies. The integration of the 50-nm-thick layer could be successfully carried out using the lift-off process. The microsensors were tested with variable thermal sequences under carbon monoxide (CO), ammonia (NH3), acetaldehyde (C2H4O), and nitrogen dioxide (NO2) which are among the main pollutant gases measured by metal-oxide (MOS) gas sensors for air quality control systems in automotive cabins. Because the microheaters were designed on a membrane, it was then possible to generate very rapid temperature variations (from room temperature to 550 °C in only 50 ms) and a rapid temperature cycling mode could be applied. This measurement mode allowed a significant improvement of the sensor response under 2 and 5 ppm of acetaldehyde.