Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe_4N, and Half-Metallic Ferromagnet: A Systematic Analysis

We theoretically analyze the anisotropic magnetoresistance (AMR) effects of bcc Fe (+), fcc Co (+), fcc Ni (+), Fe$_4$N (-), and a half-metallic ferromagnet (-). The sign in each ( ) represents the sign of the AMR ratio observed experimentally. We here use the two-current model for a system consisting of a spin-polarized conduction state and localized d states with spin--orbit interaction. From the model, we first derive a general expression of the AMR ratio. The expression consists of a resistivity of the conduction state of the $\sigma$ spin ($\sigma=\uparrow$ or $\downarrow$), $\rho_{s \sigma}$, and resistivities due to s--d scattering processes from the conduction state to the localized d states. On the basis of this expression, we next find a relation between the sign of the AMR ratio and the s--d scattering process. In addition, we obtain expressions of the AMR ratios appropriate to the respective materials. Using the expressions, we evaluate their AMR ratios, where the expressions take into account the values of $\rho_{s \downarrow}/\rho_{s \uparrow}$ of the respective materials. The evaluated AMR ratios correspond well to the experimental results.Comment: 17 pages, 12 figures, to be published in J. Phys. Soc. Jpn, minor mistakes corrected, final versio

Study of the transition from oxidation to nitriding in a single N2–H2–O2 post-discharge

International audienceThe nitriding (understood here as the reduction of native oxide present on iron samples followed by the diffusion of nitrogen in the solid) or the oxidation of a 25-μm-thick iron foil is performed in a N2–0.5 vol.% H2–0.012 vol.% O2 post-discharge by simply varying the temperature from 673 up to 773 K. The -Fe2N1−x phase is obtained at 773 K whereas the Fe3O4 phase is clearly identified at 673 K. At 723 K, either an oxide or a nitride phase is synthesized, depending on the leakage in the reactor. The measurement of the intensity of the first positive system of nitrogen indicates that the time evolution of this signal could be correlated with the growth of the oxide layer at low temperature and with the nitrogen uptake by solid diffusion at high temperature

Effects of the substrate temperature on the deposition of thin SiOx films by atmospheric pressure microwave plasma torch (TIA)

International audienceThe effect of surface temperature on the deposition of silicon oxide (SiOx) films with a non-thermal microwave axial injection torch (TIA) was investigated in an open air reactor. Argon was used as plasma gas and hexamethyldisiloxane (Si2O2C6H18) as silicon precursor. The parametric study reported here focuses on the influence of the substrate temperature on the morphological and chemical properties of the films deposited in the interval [0 °C-130 °C]. A similar effect of low and high surface temperature on the deposition process and on the microstructure of the deposited films was highlighted. Macroscopically, particles were promptly produced in the gas phase and incorporated to the film, which generates high surface roughness. Microscopically, FTIR results have shown a high carbon contamination of the deposited films at low and high temperatures, resulting in understoichiometric SiOx films. They have also demonstrated that an optimum growth window for smooth and particle free SiOx was to keep the surface temperature between 30 and 60 °C. Simple reaction mechanisms for powder formation and continuous silicon oxide thin films growth are suggested for each temperature ranges

Stoichiometric SiO2 thin films deposited by reactive sputtering

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