Spin wave propagation and spin polarized electron transport in single crystal iron films

The technique of propagating spin wave spectroscopy is applied to a 20 nm thick Fe/MgO (001) film. The magnetic parameters extracted from the position of the resonance peaks are very close to those tabulated for bulk iron. From the propagating waveforms, a group velocity of 4 km/s and an attenuation length of about 6 micrometers are extracted for 1.6 micrometers-wavelength spin-wave at 18 GHz. From the measured current-induced spin-wave Doppler shift, we also extract a surprisingly high degree of spin-polarization of the current of 83%. This set of results makes single-crystalline iron a promising candidate for building devices utilizing high frequency spin-waves and spin-polarized currents.Comment: 5 figures, submitted to Phys. Rev.

Spin wave study of magnetic perpendicular surface anisotropy in single crystalline MgO/\text{/}Fe/\text{/}MgO films

Broadband ferromagnetic resonance is measured in single crystalline Fe films of varying thickness sandwiched between MgO layers. An exhaustive magnetic characterization of the films (exchange constant, cubic, uniaxial and surface anisotropies) is enabled by the study of the uniform and the first perpendicular standing spin wave modes as a function of applied magnetic field and film thickness. Additional measurements of non-reciprocal spin wave propagation allow us to separate each of the two interface contributions to the total surface anisotropy. The results are consistent with the model of a quasi-bulk film interior and two magnetically different top and bottom interfaces, a difference ascribed to different oxidation states

Propagation des ondes de spin et sa modification par un courant électrique dans des systèmes permalloy/Al2O3, permalloy/platine et fer/MgO

Propagating spin wave measurements were realised to characterize two spin-orbit related phenomena, as well as spin dependent electrical transport. The effects of spin-orbit coupling have been studied in nickel-iron/platinum bilayers. It has been shown that in these films the frequencies of two counter-propagating spin waves are not the same, which is attributed to the combined effects of a chiral magnetic interaction named Dzyaloshinskii-Moriya interaction and an asymmetry of the magnetic properties across the film thickness. By applying an electrical current in such system we have observed a modification of the spin wave relaxation rate due to the spin transfer torque induced by spin Hall effect. On the other hand, from the study of spin wave propagation in thin epitaxial iron films at room temperature, a degree of spin polarization of the electrical current of 83% was extracted, which is attributed to a significant spin-asymmetry of the electron-phonon coupling.Des mesures d’ondes de spin propagatives ont été réalisées pour caractériser deux effets de l’interaction spin-orbite ainsi que le transport électrique dépendant du spin. Les effets du couplage spin-orbite ont été étudiés dans des bicouches nickel-fer/platine. Dans ces films, les fréquences de deux ondes de spin contre-propageantes ne sont pas les mêmes, ce qui est attribué à l’effet combiné d’une interaction magnétique chirale appelée interaction Dzyaloshinskii-Moriya et d’une asymétrie dans l’épaisseur du film magnétique. En appliquant le courant électrique dans ce système nous avons observé une modification du taux de relaxation de l’onde de spin qui est attribuée au transfert de spin induit par effet Hall de spin. D’autre part, les études de propagation d’ondes de spin dans une couche mince de fer épitaxié à température ambiante ont montré une polarisation en spin du courant électrique de 83%, ce qui est attribué à une forte asymétrie du couplage électron-phonon

Determining key spin-orbitronic parameters by means of propagating spin waves

We characterize spin wave propagation and its modification by an electrical current in Permalloy(Py)/Pt bilayers with Py thickness between 4 and 20 nm. First, we analyze the frequency non-reciprocity of surface spin waves and extract from it the interfacial Dzyaloshinskii-Moriya interaction constant $D_s$ accounting for an additional contribution due to asymmetric surface anisotropies. Second, we measure the spin-wave relaxation rate and deduce from it the Py/Pt spin mixing conductance $g^{\uparrow\downarrow}_{eff}$. Last, applying a \textit{dc} electrical current, we extract the spin Hall conductivity $\sigma_{SH}$ from the change of spin wave relaxation rate due to the spin-Hall spin transfer torque. We obtain a consistent picture of the spin wave propagation data for different film thicknesses using a single set of parameters $D_s=0.25$ pJ/m, $g^{\uparrow\downarrow}_{eff} = 3.2\times 10^{19}$ m$^{-2}$ and $\sigma_{SH}=4\times10^{5}$ S/m

Spin pumping as a generic probe for linear spin fluctuations: demonstration with ferromagnetic and antiferromagnetic orders, metallic and insulating electrical states

International audienceWe investigated spin injection by spin pumping from a spin-injector(NiFe) into a spin-sink to detect spin fluctuations in the spin-sink. By scanning the ordering-temperature of several magnetic transitions, we found that enhanced spin pumping due to spin fluctuations applies with several ordering states: ferromagnetic(Tb) and antiferromagnetic(NiO, NiFeOx, BiFeO3, exchange-biased and unbiased IrMn). Results also represent systematic experimental investigation supporting that the effect is independent of the metallic and insulating nature of the spin-sink, and is observed whether the spin current probe involves electronic or magnonic transport, facilitating advances in material characterization and engineering for spintronic applications

Cluster Approach To Model Titanium Dioxide as Isolated or Organic Dye Sensitized Nanoobjects

International audienceThis paper proposes the cluster approach methodology to simulate electronic properties of semiconducting isolated nanocrystalline materials as well as functionalized by organic dye molecules. The proposed cluster approach considers the nanoobject construction with the crystal structure in the internal part while the surface is modified according to the environmental interaction. In this aim, the (TiO2)n clusters with n = 2-140, indoline dye molecule D102, and their hybrid composites were investigated. The electronic properties of (TiO2)n were computed thanks to different DFT potentials, considering the nanobject sizes evaluation, their environmental surface modification and saturation, and the interface effects occurring between the cluster and sensitizer. The studies prove that the electronic features of (TiO2)n nanoparticles with surface being altered by the external environment may be coherently computed using DFT methodology with LC-BLYP potential by modifying the long-range separation parameter μ. The values of μ depend on the composition of the investigated system, whereas the surface saturation of the studied clusters possessing suitable size did not have any critical impact on their electronic properties. It is shown that the developed methodology is also relevant to characterize the charge transfer involved in the hybrid forms associating dye molecules and (TiO2)n clusters. The mentioned process is crucial in the efficiency of photovoltaic devices based on the hybrid systems