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This manuscript is devoted to classical mechanics and quantum mechanics, especially in the presence of magnetic field. In classical mechanics, we use Hamiltonian dynamics to describe the motion of a charged particle in a domain affected by the magnetic field. We are interested in two classical physical problems: the confinement and the scattering problem. In the quantum case, we study the spectral problem of the magnetic Laplacian at the semi-classical level, in two-dimensional domains: on a compact Riemmanian manifold with boundary and on ℝ ². Under the assumption that the magnetic field has a unique positive and non-degenerate minimum, we can describe the eigenfunctions by WKB methods. Thanks to the spectral theorem, we estimated efficiently the true eigenfunctions and the approximate eigenfunctions locally near the minimum point of the magnetic field. On ℝ ², with the additional assumption that the magnetic field is radially symmetric, we can show that the eigenfunctions of the magnetic Laplacian decay exponentially at infinity and at a rate controlled by the phase function created in WKB procedure. Furthermore, the eigenfunctions are very well approximated in an exponentially weighted space., Ce manuscrit est consacré à l'étude de la mécanique classique et la mécanique quantique en présence d'un champ magnétique. En mécanique classique, nous utilisons un Hamiltonien pour décrire la dynamique d'une particule chargée dans un domaine soumis à un champ magnétique. Nous nous intéressons ici à deux problèmes classiques de physique : le problème de confinement et le problème de scattering. Dans le cas quantique, nous étudions le problème spectral du laplacien magnétique au niveau semi-classique dans des domaines de dimension deux: sur une variété Riemanienne compacte à bord et dans ℝ ². En supposant que le champ magnétique ait un unique minimum strictement positif et non-dégénéré, nous pouvons décrire les fonctions propres par les méthodes WKB. Grâce au théorème spectral, nous pouvons estimer efficacement les vraies fonctions propres et les fonctions propres approchées localement proche du minimum du champ magnétique. Dans ℝ ², sous l'hypothèse additionnelle d'une symétrie radiale du champ magnétique, nous pouvons montrer que les fonctions propres du laplacien magnétique décroissent de manière exponentielle à l'infini avec une vitesse contrôlée par la fonction phase de la procédure WKB. De plus, les fonctions propres sont très bien approchées dans un espace à poids exponentiel.

Gas-sensing performance of the electrochemical sensor utilized solid electrolyte of yttria-stabilized zirconia (YSZ) and metal-oxide sensing-electrode (SE) depends on electrochemical catalytic reaction at interface of metal-oxide/YSZ and heterogeneous gas-phase reaction through SE oxide. In this work, the mixed potential sensors with a configuration of Pt/YSZ/(Pt-LaFeO 3 ) sintered at the temperatures T s = 700, 800, 900, 1050, 1200 and 1300 °C were investigated by exposing to various gases such as NO 2 , NO, CO, C 3 H 8 and CH 4 at the operating temperatures T o = 450, 500, 550, 600 and 650 °C. All the sensors Pt/YSZ/(Pt-LaFeO 3 ) exhibited good sensitive and selective characteristics to NO 2 gas. Interesting characteristics on the gas sensing performances were obvious that the Δ V responses to NO 2 gas obtained the minimum and maximum values when the sensors Pt/YSZ/(Pt-LaFeO 3 ) sintered at the temperatures T s = 900 and 1200 °C, respectively. Typically, the sensors exhibited decrease of NO 2 selectivity with increasing the sintering temperature T s . The t 90 response-recovery times of the sensors were relatively complicated with the sintering temperature. Effect of the sintering temperatures of the Pt/YSZ/LaFeO 3 sensors on the gas sensing performances was also discussed in detail.

In this work, the perovskite-type oxides LaMO 3 (M = Mn, Fe, Co, Ni) were utilized for sensing electrodes of the electrochemical gas sensors based on the electrolyte YSZ (ZrO 2 + 8%mol Y 2 O 3 ). The sensors with configuration of Pt/YSZ/La M O 3 were sintered at high temperature of 1200 °C in order to analyze influence of the 3 d transition metals ( M ) on gas-sensing characteristics of the perovskite-type oxide electrodes. The sensors were investigated by exposing to various gases of NO 2 , NO, CO, C 3 H 8 and CH 4 . The sensor Pt/YSZ/LaFeO 3 had the best sensitive and selective characteristics to NO 2 gas. The sensors Pt/YSZ/La M O 3 ( M = Mn, Co, Ni) showed poor gas-selectivity. Valence variation of the 3 d transition elements was used to explain the gas-sensing performance of the sensors Pt/YSZ/La M O 3 . The electrical conductance behavior of the oxides La M O 3 was also considered as an important parameter that affected to sensitivity of the sensors Pt/YSZ/La M O 3 , particularly in the high operating temperature.

We studied the relationship between the output characteristics of the meta-antenna and the structure of its surface to search for a correlation between the structure and antenna's outputs in different frequency regions. We showed that the resonance characteristics varied on the size of the unit cells but depended almost linearly on the distance between them.

We found the large magnetocaloric effect (MCE) in La 0.6 Ca 0.3 Pb 0.1 MnO 3 (sample No. 1), La 0.7 Ca 0.2 Pb 0.1 MnO 3 (sample No. 2), and La 0.7 Ca 0.1 Pb 0.2 MnO 3 (sample No. 3) perovskites, which were prepared by a conventional ceramic method. For a magnetic field change of 13.5 kOe, the magnetic entropy change (Δ S M ) reached values of 2.55, 2.53 and 3.72 J/kg K for samples Nos. 1, 2 and 3, respectively. Interestingly, the large Δ S M was found to occur around 300 K for all samples investigated, which allows magnetic refrigeration at room temperature. These perovskites have the large magnetic entropy changes induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials.

In this report, we demonstrate a comprehensive analysis of the effects of Au addition on the microstructure and magnetic properties of Fe 73.5 Si 13.5 B 9 Nb₃Au₁ Finemet-type alloy. It was found that the as-quenched alloys were the amorphous state and turned into nanocrystalline state under heat treatments. The DSC analysis indicates that the sharply exothermal peak corresponding to the crystallization of the α-Fe(Si) was observed at 547- 579℃ depending on the heating rates, which is little higher than that of original Finemet (542-570℃, respectively). Besides, the thermomagnetic result confirmed that the full substitution of Cu by Au with the single phase structure in the M(T) curve along cooling cycle. Ultrasoft magnetic properties of the nanocrystallized samples were significantly enhanced by the proper annealing such as the increase of permeability and the decrease of the coercivity. The optimum annealing condition was found at the annealing temperature of 540℃ and the increase of the annealing time up to 90 min.

A thorough study about the influences of Mn substitution for Fe on the microstructure and magnetic characteristics of Fe 73.5-x MnxSi 13.5 B 9 Nb₃Cu₁ (x = 1, 3, 5) alloys prepared by the melt-spinning technique has been performed. Nanocomposites composed of nanoscale (Fe,Mn)₃Si magnetic phase embedded in an amorphous matrix were obtained by annealing their amorphous alloys at 535℃ for 1 hour. The addition of Mn causes a slight increase in the mean grain size. The Curie temperatures of the initial amorphous phase and of the nanocrystals phase decreased, while the Curie temperature of the remaining amorphous phase remained nearly constant with increasing Mn content. Soft magnetic properties of the crystallized samples have been significantly improved by a proper thermal treatment. Accordingly, the giant magnetoimpedance effect is observed and ascribed to the increase of the magnetic permeability, and the decrease of the coercivity of the samples. The increased magnetic permeability is resulted from a decrease in the magnetocrystalline anisotropy and saturation magnetostriction.

The effect of annealing temperature on the permeability and giant magneto-impedance (GMI) behaviors of Fe 68.5 Mn 5 Si 13.5 B 9 Nb₃Cu₁ amorphous alloy has been systematically investigated. The nan℃rystalline Fe68.5Mn5- Si13.5B9Nb3Cu1 alloys consisting of ultra-fine (Fe,Mn)₃Si grains embedded in an amorphous matrix were obtained by annealing their precursor alloy at the temperature range from 500℃ to 600℃ for 1 hour in vacuum. The permeability and GMI profiles were measured as a function of external magnetic field. It was found that the increase of both the permeability and the GMI effect with increasing annealing temperature up to 535℃ was observed and ascribed to the ultrasoft magnetic properties in the sample, whereas an opposite tendency was found when annealed at 600℃ which is due to the microstructural changes caused by high-temperature annealing. The study of temperature dependence on the permeability and GMI effect showed some insights into the nature of the magnetic exchange coupling between nan℃rystallized grains through the amorphous boundaries in nan℃rystalline magnetic materials.

Magnetization, resistivity, and electron spin resonance (ESR) measurements were carried out to investigate spin dynamics, electrical and magnetic properties of (La 0.5 Pr 0.5 ) 0.7 Pb 0.3 Mn 1− x Cu x O 3 ( x = 0 , 0.02) perovskites. It was found that with Cu addition the Curie temperature decreased from 326 K for x =0 to 300 K for x = 0.0 2 composition. The x = 0 sample underwent a metallic–insulator transition at ∼130 K, whereas the x = 0.0 2 sample with higher resistivity exhibited an insulating behavior as a whole. It was furthermore found that asymmetrical ESR signals at low temperatures became Lorentzian at high temperatures above T min . The temperature dependence of the linewidth, Δ H ( T ) , at T > T min fits well to the one-phonon model, Δ H ( T ) = AT + B . The activation energy E a , determined from the ESR intensity with respect to temperature, are 0.16 and 0.14 eV for x = 0 and 0.02 compositions, respectively. In terms of our experimental results, it is reasonable to conclude that the Cu addition led to a suppression of the ferromagnetism and conductivity of the parent compound ( x = 0 ).

Magnetic entropy change above 300 K, which is larger than that of gadolinium (Phys. Rev. B 57 (1998) 3478), has been observed in a Cu-doped manganites of La0.7Sr0.3Mn1−xCuxO3 ( x = 0.05 , 0.1 ). The large magnetic entropy change originated from a sharp magnetization jump is associated with a first-order crystallographic phase transition of the sample near the Curie temperature. These results suggest that the present Cu-doped manganites are suitable candidate materials for magnetic refrigerants in the room temperature magnetic-refrigeration technology.

We present the results of an investigation on the magnetocaloric effect in the perovskites of La{sub 0.845}Sr{sub 0.155}Mn{sub 1-x}M{sub x}O{sub 3} (M = Mn, Cu, Co). It is found that there was a large magnetic entropy change, i.e. a large magneto-caloric effect, in all these samples. Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu-doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology. The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic-paramagnetic transition temperature (T{sub C}) - which is experimentally verified by electron paramagnetic resonance study. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Structural, magnetic, magnetocaloric and magnetoresistance (MR) studies on La0.7Sr0.3Mn0.95Cu0.05O3 (No. 1) and La0.7Sr0.3Mn0.9Cu0.1O3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermomagnetic measurements for both compositions at low field indicate that a spin–glass-like state (or cluster glass) occurs at low temperatures and a very sharp change of magnetization around the phase-transition point. The Curie temperature, TC, does almost not depend on the content of Cu substitution. A maximum magnetic-entropy change, ΔSmax, of 1.96 and 2.07 J/kg K at 13.5 kOe and 350 K is observed for sample No. 1 and No. 2, respectively. Therefore, they can be considered as active magnetic refrigerant materials for room-temperature applications. Electrical-resistance measurements show that both samples are metallic conductor for T TC; moreover, the MR is maximal around TC.

La 1− x Pb x MnO 3 ( x =0.1, 0.2, 0.3, 0.4, and 0.5) perovskites were prepared by a solid-state reaction. Except for x =0.5 (cubic) and x =0.4 (rhombohedral), the structure of the other compositions was pseudo-rhombohedral with P1 symmetry. The particle size of the grains is depending on the Pb content of the samples. The Curie temperature T c increases from 235 K for x =0.1–310 K for x =0.2 and is almost constant (about 360 K) for x ⩾0.3. The field-cooled and zero-field-cooled thermomagnetic curves measured at low field show a split below a so-called irreversibility temperature T r , which is somewhat smaller than T c except for x =0.1, where it is 270 K. From a series of magnetic isotherms the magnetic entropy changes Δ S ( T ) were determined for a field step of 500 Oe. The maximum value of Δ S max increases with increasing x till x =0.3 and then decreases with further increasing x . The conductivity of perovskites is metallic at low temperatures and semiconducting at high temperatures. Magnetoresistance measurements have been performed.

Conference on International Magnetics (INTERMAG), Taipei, TAIWAN, APR 25-29, 2011; International audience; The structure and optical properties of artificial opal thin films, which were synthesized from silica spheres by a modified self-assembly protocol, in the absence and under the applied magnetic field were studied. The surface characterization showed a homogeneous well-ordered face centered cubic structure of silica balls at average size 305 +/- 5 nm. The reflection measurements showed the main reflection plane (1 1 1) besides a minor secondary (2 0 0) plane. The applied field (up to 1000 Oe) induced a systematical splitting of several lines which showed an increase in intensity according to the increase in applied field and thickness of substrate coating MnO(2) layer.

Influence of Mn partial substitution for Fe on the magnetic and magnetoimpedance properties of Fe 73.5-x Mn x Si 13.5 B 9 Nb 3 Cu 1 ( x = 1, 3, and 5) nanocomposite ribbons were investigated. The results indicated that the Mn addition led to an improved exchange coupling between grains and hence in the magnetic softness. Consequently, the giant magnetoimpedance (GMI) effect was significantly enhanced in these nanocomposites. In the frequency range of 0.1-10 Mhz, the GMI ratio reached the highest values of 83%, 94%, and 130% at the frequency of 2 MHz for x = 1, 3, and 5 compositions, respectively. The corresponding field sensitivity of GMI reached the highest values of 6, 7, and 16 %/Oe, respectively. These indicate that Fe 73.5-x Mn x Si 13.5 B 9 Nb 3 Cu 1 ( x = 1, 3, and 5) nanocomposites are potential candidate materials for making GMI sensors.