Search

Ir and Pt thickness dependences of the interfacial Dzyaloshinskii-Moriya interaction (iDMI), the perpendicular magnetic anisotropy (PMA), and the damping in Co-based systems grown by sputtering on Si substrates, using Ir or Pt under or overlayer of variable thickness ($0\ensuremath{\le}{t}_{\mathrm{Pt}}\ensuremath{\le}3.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ and $0\ensuremath{\le}{t}_{\mathrm{Ir}}\ensuremath{\le}1.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$), were investigated using Brillouin light scattering. Vibrating sample magnetometry measurements revealed a significant decrease of the areal magnetic moment at saturation as the thickness ${t}_{\mathrm{Pt}}$ or ${t}_{\mathrm{Ir}}$ of the overlayer increases, most likely due to the increasing intermixing. The intermixing, found to be negligible for Ir and Pt underlayers, is stronger for Ir than Pt overlayers. Damping measurements for Pt-based systems allowed us to conclude with the strong spin-pumping contribution. The analysis of the ${t}_{\mathrm{Pt}}$ dependence of damping, within the spin-pumping model, allowed us to determine the spin-diffusion length of Pt, found to be greater when Pt is used as an underlayer. The ${t}_{\mathrm{Pt}}$ dependence of the effective PMA and iDMI constants, for which similar trends to that of damping were observed, were qualitatively analyzed to separate the contribution of each interface with Co. It was found that these constants are stronger when Co is grown on Pt, most probably due to weaker intermixing at the Pt/Co interface. Linear dependence of damping vs the PMA effective constant was evidenced, confirming their relationship with spin-orbit coupling (SOC). A linear variation of the PMA effective constant vs the iDMI constant was observed in systems using Pt underlayer, whereas quadratic or linear correlations are possible when Pt is used as an overlayer, probably due to change of the interface SOC by the strong intermixing at the Co/Pt interface. The qualitative analysis of the Ir thickness dependence of iDMI and PMA constants revealed a significant (weak) contribution of the Ir/Co interface to PMA (iDMI). The surface iDMI constant of the Co/Ir interface was estimated to be 0.4 \ifmmode\pm\else\textpm\fi{} 0.1 pJ/m, which confirms the similar iDMI sign of Co/Ir and Co/Pt interfaces.

Vibrating sample magnetometery (VSM) combined with Brillouin light scattering (BLS) were used to investigate the Dzyaloshinskii-Moriya interaction (iDMI), the perpendicular magnetic anisotropy (PMA) and the damping in ${\mathrm{Co}}_{0.5}{\mathrm{Fe}}_{0.5}$-based systems grown by sputtering on $\mathrm{Si}/{\mathrm{SiO}}_{2}$ substrates, using Pt or Cu buffer layers and Hf capping layer of variable thickness $(0\ensuremath{\le}{t}_{\mathrm{Hf}}\ensuremath{\le}2\phantom{\rule{0.28em}{0ex}}\mathrm{nm})$. VSM measurements revealed a significant decrease of the areal magnetic moment at saturation as ${t}_{\mathrm{Hf}}$ increases, most likely due to the increase of the magnetic dead layer thickness at CoFe/Hf interface up to $0.73\ifmmode\pm\else\textpm\fi{}0.06\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for ${t}_{\mathrm{Hf}}=2\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$. Damping measurements allowed concluding to the weaker spin pumping contribution by the CoFe/Hf interface compared to Pt/CoFe. The analysis of the ${t}_{\mathrm{Hf}}$ dependence of damping within a model considering the contribution of each interface allowed us to determine the spin diffusion length of Hf, found to be 1.7 nm. The Hf thickness dependence of iDMI and PMA constants revealed significant (weak) contribution of the CoFe/Hf interface to PMA (iDMI). The surface iDMI constant of CoFe/Hf interface was estimated to be $(\ensuremath{-}0.37\ifmmode\pm\else\textpm\fi{}0.12)\ifmmode\times\else\texttimes\fi{}{10}^{--7}\phantom{\rule{0.28em}{0ex}}\mathrm{erg}/\mathrm{cm}$. This suggests that the iDMI sign of Hf and Pt are opposite, and an additive behavior can be obtained when they are placed in opposite sides of the CoFe layer, allowing thus to strengthen the iDMI, needed for some applications. Quadratic correlations between PMA and iDMI constants and linear dependence of damping versus PMA constant were obtained confirming their relationship with the spin-orbit coupling.

Ab initio calculations of voltage-controlled perpendicular magnetic anisotropy predict that the adjunction of Pt at the top of Co/MgO interface in Pt/Co/MgO ultrathin structures would enhance the perpendicular anisotropy and its electric field ( $E$ -field) variation rate. Following these theoretical expectations, using the magnetron-sputtering technique, we first designed and elaborated magnetic multilayered samples which have subsequently been patterned by UV lithography in magnetotransport devices. The as-deposited samples show perpendicular magnetization configuration whose $E$ -field modulation has been studied by anomalous Hall effect magnetometry experiments under applied $E$ -field in patterned devices. The measured voltage anisotropy modulation effect is found to be asymmetric with respect to the $E$ -field polarity, in qualitative agreement with theoretical predictions.

Microstrip line ferromagnetic resonance (MS-FMR) and Brillouin light scattering (BLS) in the Damon-Eshbach geometry were used to investigate the perpendicular magnetic anisotropy (PMA), the damping and the interfacial Dzyaloshinskii-Moriya (iDMI) interaction in ferromagnetic $(\mathrm{FM})/\mathrm{Ta}{\mathrm{O}}_{x}\text{\ensuremath{-}}\mathrm{based}$ systems as a function of the ferromagnetic ($\mathrm{FM}=\mathrm{Co}$ or ${\mathrm{Co}}_{8}{\mathrm{Fe}}_{72}{\mathrm{B}}_{20}$) and the $\mathrm{Ta}{\mathrm{O}}_{x}$ thicknesses (oxidation level). The analysis of the experimental FMR and BLS data has shown that the effective magnetization, the Gilbert damping parameter \ensuremath{\alpha} and the iDMI are inversely proportional to the CoFeB and the Co films thickness. The BLS investigation of the iDMI variation versus the $\mathrm{Ta}{\mathrm{O}}_{x}$ thickness and oxidation level reveals a contribution of $\mathrm{FM}/\mathrm{Ta}{\mathrm{O}}_{x}$ mediated by the presence of a Rashba field at this interface. Finally, we evidenced a correlation between iDMI and PMA by varying the Cu spacer thickness in the $\mathrm{Pt}/\mathrm{Cu}/\mathrm{Co}/\mathrm{Ta}{\mathrm{O}}_{x}$ system and we showed that both PMA and iDMI are localized at the first atomic monolayers of the Pt/Co interface. The observed non-linear dependence of PMA versus iDMI constant is attributed to similar interface orbital hybridizations involved in both quantities.

The perpendicular magnetic anisotropy (PMA) and the interfacial Dzyaloshinskii-Moriya interaction (iDMI) are investigated in as grown and 300 °C annealed Co-based ultrathin systems. For this, Co films of various thicknesses (0.8 nm ⩽ t Co ⩽ 5.7 nm) were deposited by magnetron sputtering on thermally oxidized Si substrates using Pt, W, Ir, Ti, Ru and MgO buffer or/and capping layers. X-ray diffraction was used to investigate their structural properties and vibrating sample magnetometry (VSM) was used to determine the magnetic dead layer thickness and the magnetization at saturation (M s). VSM revealed that the M s for the Pt and the Ir buffered and capped films is the largest. Microstrip line ferromagnetic resonance (MS-FMR), used to extract the gyromagnetic ratio of the thicker Co films, revealed the existence of a second order PMA term, which is thickness dependent. Brillouin light scattering (BLS) in the Damon-Eshbach configuration was used to investigate the thickness dependence of the iDMI effective constant from the spin wave vector dependence of the frequency difference between Stokes and anti-Stokes lines. BLS and MS-FMR techniques were combined to measure the spin wave frequency variation as a function of the in-plane applied magnetic field (where the second order PMA contribution vanishes). The thickness dependence of the effective magnetization was then deduced and used to investigate PMA. For all the systems, PMA results from interface and volume contributions that we determined. The largest interface PMA constants were obtained for Pt- and Ir-based systems due to the electron hybridization of Co with these heavy metals having high spin orbit coupling. Annealing at 300 °C increases both the interface PMA and iDMI for the Pt/Co/MgO most probably due to de-mixing of interpenetrating oxygen atoms from the Co layer and the formation of a sharp Co/O interface.

International audience

Epitaxial magnetic heterostructures of $\mathrm{Mg}\mathrm{O}(001)//\mathrm{Pd}/{\mathrm{Co}}_{2}\mathrm{Fe}\mathrm{Al}/\mathrm{Mg}\mathrm{O}$ are grown by magnetron sputtering and the current-induced spin-orbit torques are quantified using harmonic Hall measurements. We demonstrate efficient current-induced spin-orbit-torque switching in perpendicularly magnetized samples. The advantage of such heterostructures for spin-orbit-torque magnetic random-access memory devices is that they allow a combination of critical ingredients: (i) the low resistivity required for reduced electric energy consumption during writing, (ii) the compatibility with a high tunnel magnetoresistive ratio required for efficient reading, and (iii) strong perpendicular magnetic anisotropy for increased thermal stability.

Co20Fe60B20 thin films of various thicknesses (3 nm $\le t_{\text {CFB}} \le 14$ nm) have been sputtered on thermally oxidized Si substrates and capped with 8 nm-thick Ir or Ru layers and then annealed at 400 °C. A vibrating sample magnetometer has been used to measure the CoFeB thickness dependence of the saturation magnetic moment per unit area in order to straightforwardly determine the magnetization at saturation and the magnetic dead layer thickness, found to be 1115 ± 50 emu/cm3 (930 ± 50 emu/cm3) and 1.53 nm (0.76 nm) for the as-deposited CoFeB/Ir (CoFeB/Ru) sytems, respectively. These values change to 1185 ± 50 emu/cm3 (1110±50 emu/cm3) and 2.93 nm (1.62 nm) for CoFeB/Ir (CoFeB/Ru) films annealed at 400 °C. Microstrip ferromagnetic resonance (MS-FMR) was used to investigate the Gilbert damping parameter and the magnetic anisotropy as a function of the CoFeB thickness. While the in-plane anisotropy field for the as-deposited films does not show a regular behavior versus the CoFeB thickness, a clear linear behavior of this field versus the reciprocal CoFeB effective thickness can be observed for the annealed samples. Moreover, the effective magnetization varies linearly with the inverse effective thickness of CoFeB due to the perpendicular interface anisotropy. This surface anisotropy constant, which was estimated to be 0.84 and 0.89 erg/cm2 for the as-deposited CoFeB films capped with Ir or Ru, respectively, reinforces the perpendicular easy axis. The corresponding anisotropy constants for the annealed Ir and Ru capped films are found to be 1.07 and 0.57 erg/cm2, respectively. Moreover, MS-FMR results revealed that the damping constant increases linearly with the reciprocal effective thickness of CoFeB, most probably due to spin pumping. The effective spin mixing conductance of the as-deposited (annealed) CoFeB/Ru and CoFeB/Ir has been estimated to be 12.93 nm−2 (22.4 nm−2) and 29.3 nm−2 (43.85 nm−2), respectively.

Brillouin light scattering (BLS) combined with vibrating sample magnetometry (VSM) have been used to investigate the Dzyaloshinskii–Moriya interaction (DMI) in Pt-buffered Co2FeAl0.5Si0.5 ultrathin films of various thicknesses. VSM measurements of the Co2FeAl0.5Si0.5 (CFAS) thickness dependence of the saturation magnetic moment per unit area revealed a magnetization at saturation of 1286 emu/cm3 and 0.31 nm magnetic dead layer. Furthermore, thickest films ( $t_{{\text {CFAS}}} >1$ nm) are in-plane magnetized, while the thinner ones are perpendicular magnetized. BLS measurements, in the Damon–Eshbach geometry, under an in-plane applied magnetic field revealed the non-reciprocity of the spin waves (SWs) propagating in opposite directions (Stokes and anti-Stokes lines) due to the Pt-induced DMI. Stokes and anti-Stokes lines’ frequency mismatch varies linearly as function of the SW vector allowing the determination of the effective DMI constant. Its thickness dependence leads to determine a value of −0.42 pJ/m for the DMI interface constant, which is significantly lower than that of Pt/Co/AlO x films. Moreover, BLS measurements revealed that the effective magnetization varies linearly with the reciprocal effective CFAS thickness due to the perpendicular interface anisotropy, estimated to be 0.49 mJ/m2, which reinforces the perpendicular magnetization easy axis.

This paper describes the synthesis and characterization of YBa2Cu3O7−x (YBCO) nanoparticles obtained through an environmentally friendly chemistry approach. Y-, Cu- acetates and Ba trifluoroacetate were used for the synthesis of the precursor gel. Moreover, sucrose and pectin reagents were added as chelating agents inducing the formation of small size oxide nanoparticles. The thermal decomposition process of the precursor powder was investigated by thermal analysis correlated with mass spectrometry. The chemical nature, structure and morphology of the particles were investigated by X-Ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy. According to XRD analysis the nanoparticles have an orthorhombic structure and the average diameter between 18–30 nm, additionally confirmed by TEM measurements. The superparamagnetic behavior at room temperature of the YBCO nanoparticles has been clearly evidenced by magnetization measurements. Furthermore, the effect of the annealing atmosphere on the magnetic properties has been studied.

This paper presents a comparative study regarding the preparation of Fe-based amorphous alloys via mechanical alloying (MA) and rapid quenching (RQ). The obtained samples (powders and ribbons) were characterised by X-ray diffraction (XRD), in-situ high-temperature X-ray diffraction (HT-XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) and vibrating sample magnetometry (VSM). By using elemental powders of Fe, Si and B, it was found that amorphisation cannot be achieved by dry MA or RQ. Wet MA using benzene as process control agent (PCA) led to the alloy amorphisation after 20 h of milling. It was proved that the amorphisation via wet MA is possible due to the extra amount of C atoms provided by the PCA decomposition. Using powders obtained by wet MA or a mixture of Fe, Si, B and C elemental powder, amorphous ribbons were obtained by RQ. During the amorphous samples crystallisation, a mixture of α-Fe(Si) and Fe borides is formed. The magnetic measurements showed that the magnetic characteristics of the samples are strongly influenced by the technique used for their preparation.

Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a key ingredient for the development of electrically controlled spintronic devices. Due to their relatively large spin-polarization, high Curie temperature and low Gilbert damping the Co-based full Heusler alloys are of special importance from a scientific and applications point of view. Here, we study the mechanisms responsible for the PMA in Pt/Co-based full Heusler alloy/MgO thin films structures. We show that the ultrathin Heusler films exhibit strong PMA even in the absence of magnetic annealing. By means of ferromagnetic resonance experiments, we demonstrate that the effective magnetization shows a two-regime behavior depending on the thickness of the Heusler layers. Using Auger spectroscopy measurements, we evidence interdiffusion at the underlayer/Heusler interface and the formation of an interfacial CoFe-rich layer which causes the two-regime behavior. In the case of the ultrathin films, the interfacial CoFe-rich layer promotes the strong PMA through the electronic hybridization of the metal alloy and oxygen orbitals across the ferromagnet/MgO interface. In addition, the interfacial CoFe-rich layer it is also generating an increase of the Gilbert damping for the ultrathin films beyond the spin-pumping effect. Our results illustrate that the strong PMA is not an intrinsic property of the Heusler/MgO interface but it is actively influenced by the interdiffusion, which can be tuned by a proper choice of the underlayer material, as we show for the case of the Pt, Ta and Cr underlayers., 23 pages, 9 figures

The paper presents the design and characterization of multilayered spin valve structures to be used as magnetic field sensor. To enhance the performance of the sensor and to reduce the density of magnetic domain formation, two geometries of the magnetoresistive element are investigated. A meander structure element and a yoke configuration are designed with different parameters such as the width of the stripe (4 µm ÷ 8 µm), length and number of segments on a 10 mm x 20 mm mask. UV photolithography is used for micrometric patterning of the geometric shapes. The response of the as obtained devices is characterized in terms of the magnetoresistive ratio by measuring the variation curves of the electrical resistance when applying an external magnetic field.

We demonstrate room-temperature stabilization of dipolar magnetic skyrmions with diameters in the range of $100$ nm in a single ultrathin layer of the Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy magnetometer operating in the photoluminescence quenching mode. We first demonstrate skyrmion nucleation by spin-orbit torque and show that its efficiency can be significantly improved using tilted magnetic fields, an effect which is not specific to Heusler alloys and could be advantageous for future skyrmion-based devices. We then show that current-induced skyrmion motion remains limited by strong pinning effects, even though CFA is a magnetic material with a low magnetic damping parameter., 5 pages, 4 figures

25 nm to 50 nm Co2FeAl (CFA) thick wire arrays with varying widths and spacing have been patterned from continuous CFA films deposited on MgO(001) using e-beam lithography and Ar ion milling. Magneto-optical Kerr effect, transverse bias initial inverse susceptibility and torque measurements reveal that the in-plane magnetic anisotropy of the wires is dominantly monitored by a uniaxial term, in contrast with the continuous films where it is governed by the superposition of a fourfold term and of a smaller uniaxial term. The microstrip ferromagnetic resonance spectra performed using a magnetic field H, applied in the plane of the studied sample along various directions, or perpendicularly to this plane, gave us access to various quantized modes originating from the patterning. In addition, Brillouin light scattering also exhibits quantized modes. A large part of the experimental observations can be quantitatively interpreted as resulting from the demagnetizing terms induced by the geometrical patterning. However, the presented model, simply built on the effect of the demagnetizing field, is not able to give account of all the quantized modes present in the resonance spectra. When H is parallel to the wires, a more complete description is used: it considers the wave-vector quantization induced by the patterning. For the magnetic modes concerned by both approaches, the correspondence between the 2 models is easily established. When H is not parallel to the wires quantitative descriptions of the behavior of the field dependence of the observed modes still can often be performed. Finally, in all the studied patterned samples, the uniform magnetic mode, termed “film mode”, relative to the parent continuous film is observed by ferromagnetic resonance: such a behavior, which has been reported previously, remains to be completely interpreted.

This study presents the preparation and characterisation of soft magnetic composites (SMCs) in which the powders, that are generally used as the ferromagnetic phase, are replaced by short and thin Fe fibres. The Fe fibres (length of 3–7 mm and thickness of 70–110 μm) were coated with a layer of polymer that represents 1 wt% of the total weight of the fibres. To prepare the toroidal cores, three different mould filling techniques were used with the aim of orienting the fibres with their long axis parallel to the magnetising field. The compaction pressure for the preparation of all compacts was 700 MPa. The fibres used in this study were characterised via scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The degree of fibres orientation inside the composite compacts was analysed via energy-dispersive X-ray spectroscopy (EDX). The fibres based composite compacts were analysed in static (DC) and dynamic (AC) magnetisation regime up to the frequency of 10 kHz. The DC and AC magnetisation measurements highlighted that the magnetic characteristics of the compacts increase upon increasing the degree of fibres orientation. A comparison of AC and DC magnetic characteristics of a fibres-based composite and a powder-based composite (prepared in identical conditions) is presented and discussed.

Correlation between interfacial Dzyaloshinskii–Moriya interaction (iDMI), perpendicular magnetic anisotropy (PMA) and spin pumping-induced damping was investigated in CoFeB-based systems grown by sputtering on Si substrates, using Pt, Ta, Cu, W and MgO capping layers. Vibrating sample magnetometer, Brillouin light scattering (BLS) and broadband ferromagnetic resonance techniques were combined for this aim. The CoFeB thickness dependence of iDMI and PMA constants, in CoFeB/X (where X = Pt, Cu/Pt, Ta/Pt or W/Al), revealed that only the CoFeB/Pt system presents a measurable iDMI and that the interfacial PMA is mostly similar except for the Ta/CoFeB/Ta/Pt system. Therefore, no clear correlation between the above-mentioned interfacially-driven and spin-orbit coupling related quantities was observed due to their different origins in our systems. An efficient sample design involving various spacer layers of variable thicknesses in Ta/CoFeB(1.5 nm)/Y/Pt (where Y = Cu, Ta, MgO) allowed evidence of a linear correlation between iDMI, PMA constants and the effective spin mixing conductance. The linear dependence, which could result from the narrow variation range of PMA and/or iDMI, is attributed to the similar interface orbital hybridizations involved in PMA, iDMI and spin pumping-induced damping.

The interfacial Dzyaloshinskii-Moriya interaction (IDMI) is investigated in Co2FeAl (CFA) ultrathin films of various thicknesses (0.8 nm ≤ tCFA ≤ 2nm) grown by sputtering on Si substrates, using Pt, W, Ir, and MgO buffer or/and capping layers. Vibrating sample magnetometry reveals that the magnetization at saturation (Ms) for the Pt- and Ir-buffered films is higher than the usual Ms of CFA due to the proximity-induced magnetization (PIM) in Ir and Pt estimated to be 19% and 27%, respectively. The presence of PIM in these materials is confirmed using x-ray resonant magnetic reflectivity. Moreover, while no PIM is induced in W, higher PIM is obtained with Pt when it is used as a buffer layer rather than a capping layer. Brillouin light scattering in the Damon-Eshbach geometry is used to investigate the thickness dependences of the IDMI constants from the spin-wave nonreciprocity and the perpendicular anisotropy field versus the annealing temperature. The IDMI sign is found to be negative for Pt / CFA and Ir / CFA, while it is positive for W / CFA. The thickness dependence of the effective IDMI constant for stacks involving Pt and W shows the existence of two regimes similar to that of the perpendicular anisotropy constant due to the degradation of the interfaces as the CFA thickness approaches a critical thickness. The surface IDMI and anisotropy constants of each stack are determined for the thickest samples where a linear thickness dependence of the effective IDMI constant and the effective magnetization are observed. The interface anisotropy and IDMI constants investigated for the Pt / CFA / MgO system show different trends with the annealing temperature. The decrease of the IDMI constant with increasing annealing temperature is probably due to the electronic structure changes at the interfaces, while the increase of the interface anisotropy constant is coherent with the interface quality and disorder enhancement.

$\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}$ (CFA) ultrathin films, of various thicknesses $(0.9\phantom{\rule{0.28em}{0ex}}\mathrm{nm}\ensuremath{\le}{t}_{\mathrm{CFA}}\ensuremath{\le}1.8\phantom{\rule{4pt}{0ex}}\mathrm{nm})$, have been grown by sputtering on Si substrates, using Ir as a buffer layer. The magnetic properties of these structures have been studied by vibrating sample magnetometry (VSM), miscrostrip ferromagnetic resonance (MS-FMR), and Brillouin light scattering (BLS) in the Damon-Eshbach geometry. VSM characterizations show that films are mostly in-plane magnetized and the saturating field perpendicular to the film plane increases with decreasing CFA thickness suggesting the existence of a perpendicular interface anisotropy. The presence of a magnetic dead layer of 0.44 nm has been detected by VSM. The MS-FMR with the magnetic field applied perpendicularly to the film plane has been used to determine the gyromagnetic factor. The BLS measurements reveal a pronounced nonreciprocal spin wave propagation, due to the interfacial Dzyaloshinskii-Moriya interaction (DMI) induced by the Ir interface with CFA, which increases with decreasing CFA thickness. The DMI sign has been found to be the same (negative) as that of Pt/Co, in contrast to the ab initio calculation on Ir/Co, where it is found to be positive. The thickness dependence of the effective DMI constant shows the existence of two regimes similarly to that of the perpendicular anisotropy constant. The surface DMI constant ${D}_{s}$ was estimated to be $\ensuremath{-}0.37\phantom{\rule{0.16em}{0ex}}\mathrm{pJ}/\mathrm{m}$ for the thickest samples, where a linear thickness dependence of the effective DMI constant has been observed.

Co2FeAl (CFA) thin films of various thicknesses (1 nm $\le d \le 10$ nm) have been grown on (001) MgO single-crystal substrates and annealed at different temperatures ( $T_{a}$ ). Their magnetic properties have been studied by vibrating sample magnetometry, broadband microstrip ferromagnetic resonance (MS-FMR), and Brillouin light scattering (BLS). The effective magnetization, deduced from the fit of MS-FMR and BLS measurements, linearly decreases with the inverse thickness ( $1/d$ ) for all the annealing temperatures. This allows quantifying perpendicular surface anisotropy constants of 1.46, 1.71, and 1.29 erg/cm2 for $T_{a} = 215$ °C, 265 °C, and 315 °C, respectively. The perpendicular magnetization is achieved for the CFA films below a critical thickness that increases with increasing $T_{a}$ . Moreover, the fourfold anisotropy fields, measured in the in-plane magnetized films, increase with $T_{a}$ and decrease with respect to the CFA inverse thickness.

We report a detailed study of the temperature dependence of the magnetic anisotropy in Ta/Co2FeAl/MgO structures by means of Anomalous Hall Effect measurements. The volume magnetic anisotropy, although negligible at room temperature, shows a non-negligible value at low temperatures and favors an in-plane easy magnetization axis. The surface magnetic anisotropy, which promotes the perpendicular magnetic easy axis, shows an increase from 0.76 ± 0.05 erg / cm 2 at 300 K, up to 1.08 ± 0.04 erg / cm 2 at 5 K, attributed to the evolution of the Co2FeAl layer saturation magnetization with temperature.

This study investigates chemically decorated surfaces as tools for the improvement of transport properties in superconducting YBa 2 Cu 3 O 7-x films. This approach, still to be thoroughly investigated, makes use of low-cost easily tunable chemical methods to obtain self-assembled oxide nanostructures on a substrate that will serve, in a second step, for the deposition of the superconducting film itself. The structures are supposed to produce in the superconducting matrix a specific amount of strain, which is generally held responsible for the increased transport capacity of variously doped samples. For the growth of the nanostructures, two different methods have been employed: polymer-assisted deposition and metal-organic decomposition (MOD). The main advantages and disadvantages of these two routes are discussed. The oxide chosen for the deposition is one commonly used for artificial pinning in YBa 2 Cu 3 O 7-x , namely Ba 2 YNbO 6 , together with the less common but highly interesting ferromagnetic compound La 0,77 Sr 0,33 MnO 3 . We also show how the density of these nanostructures can be easily controlled, and the necessary requirements for the growth of nanostructures are determined. A variety of crystalline substrates were tested for the deposition of the nanoparticles, such as SrTiO 3 , YSZ, MgO. YBa 2 Cu 3 O 7-x films have been deposited on selected samples via standard low-fluorine MOD and characterized scanning electron microscopy (SEM), x-ray diffraction (XRD), vibrating sample magnetometer (VSM), direct current (DC) resistivity, and critical current measurements. The presence of the nanostructures results, in this case, in a slight increased value of J c , which can be ascribed to the relatively low density of nanoparticles.

International audience

Interface Dzyaloshinskii-Moriya interactions (iDMIs) in interlayer exchange coupled (IEC) Pt/${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$(1.12 nm)/Ru/${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$(1.12 nm) systems have been studied theoretically and experimentally. A vibrating sample magnetometer has been used to measure their magnetization at saturation and their interlayer exchange coupling constants. The latter are found to be of an antiferromagnetic nature for the investigated Ru range thickness ($0.5\text{--}1\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$). Their dynamic magnetic properties were studied using the Brillouin light scattering (BLS) technique. The BLS measurements reveal pronounced nonreciprocal spin-wave propagation. In contrast to the calculations for symmetrical IEC CoFeB layers, this experimental nonreciprocity is Ru thickness and thus coupling strength dependent. Therefore, to explain the experimental behavior, a theoretical model based on the perpendicular interface anisotropy difference between the bottom and top CoFeB layers has been developed. We show that the Ru thickness dependence of the spin-wave nonreciprocity is well reproduced by considering a constant iDMI and different perpendicular interfacial anisotropy fields between the top and bottom CoFeB layers. This anisotropy difference has been confirmed by the investigation of the CoFeB thickness dependence of the effective magnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linear behavior has been observed.

Zn 1− x Co x O ( x ==0.05, 0.10, 0.15) nanoparticles have been synthesized by an alternative wet-chemical synthesis route using the SimAdd technique. The as-obtained powders were investigated by FT-IR spectroscopy, X-ray diffraction and thermal analysis correlated with evolved gas analysis (TG–DTA–FT-IR) in order to determine their chemical nature, crystalline structure and to establish the decomposition sequences. The precipitates are generally amorphous, but low-intensity reflection peaks assigned both to the zinc oxalate dihydrate, and zinc hydroxide can be observed in the recorded patterns, indicating that hydroxy-oxalate precipitates were obtained. The structure, morphology and magnetic properties of the thermally treated samples have been investigated by X-ray diffraction, FT-IR, HRTEM, SAED, UV–vis and EPR. XRD studies reveal a hexagonal wurtzite-type structure for all Zn 1− x Co x O samples. TEM investigations show particle size between 28 and 37 nm, with spherical and polyhedral shapes and with tendency to form aggregates. The presence of a Co 3 O 4 secondary phase was evidenced by XRD, UV–vis and EPR for the Zn 0.85 Co 0.15 O sample. The ferromagnetic behavior of the samples was revealed. The paper highlights that by varying the cobalt concentration it is possible to modulate the structural, morphological, optical and magnetic properties.

Equipe 101 : Nanomagnétisme et électronique de spin; International audience; We report on spin polarization reduction by incoherent tunneling in single crystal Co2FeAl/MgO/Co50Fe50 magnetic tunnel junctions (MTJs). A large density of misfit dislocations in the Heusler based MTJs has been provided by a thick MgO barrier and its 3.8% lattice mismatch with the Co2FeAl electrode. Our analysis implicates a correlated structural-transport approach. The crystallographic coherence in the real space has been investigated by High Resolution Transmission Electron Microscopy phase analysis. The electronic transport experiments in variable temperature, fitted with a theoretical extended-Glazman-Matveev model, address different levels of the tunneling mechanisms from direct to multi-center hopping. We demonstrate a double impact of dislocations, as extended defects, on the tunneling polarization. Firstly, the breaking of the crystal symmetry destroys the longitudinal and lateral coherence of the propagating Bloch functions. This affects the symmetry filtering efficiency of the Delta(1) states across the (001) MgO barriers and reduces the associated effective tunneling polarization. Secondly, dislocations provide localized states within the MgO gap. This determines temperature activated spin-conserving inelastic tunneling through chains of defects which are responsible for the one order of magnitude drop of the tunnel magnetoresistance from low to room temperature.

ZnO nanoparticles were synthesized by the precipitation method, with and without tetraethylammonium hydroxide (TEAH) addition. FTIR analysis was performed for the characterization of ZnO precursors. The as-obtained ZnO nanoparticles were analyzed by X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM/TEMs) in order to observe the structural and morphological properties of the samples. The ZnO sample, obtained from the precursor containing TEAH, thermally treated at 700 °C for 2 h, shows a compact structure with polygonal particles, having crystallites size around 42 nm. The correlation between morpho-structural characteristics and the optical properties of the as-obtained samples was mainly investigated.

Undoped and holmium-doped ZnO thin films were obtained, using the sol-gel method. The films were characterized by scanning electron microscopy (SEM), Hall effect measurements, electron paramagnetic resonance (EPR) spectroscopy and superconducting quantum interference device vibrating sample magnetometry (SQUID-VSM). The Hall effect measurements have indicated a n-type conduction with a resistivity of about 3.2 Ω.cm for the undoped ZnO and of about 4.5 Ω.cm for the 5 at. % Ho-doped ZnO thin films. The EPR measurements have indicated the presence of interstitial zinc in the undoped ZnO and the presence of zinc vacancies in 5 at. % Ho-doped ZnO. Ho (5 at. %)-doped ZnO films exhibit superparamagnetism at 5 K, while a low paramagnetic behavior was observed at room temperature.

$\mathrm{C}{\mathrm{o}}_{0.5}\mathrm{F}{\mathrm{e}}_{0.5}$ (CoFe) ultrathin films of various thicknesses $(0.8\phantom{\rule{0.16em}{0ex}}\mathrm{nm}\ensuremath{\le}{t}_{\mathrm{CoFe}}\ensuremath{\le}1.6\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$ have been grown by sputtering on (001) MgO single crystal or Si/${\mathrm{SiO}}_{2}$ substrates, using Pt as capping or buffer layers, respectively. The x-ray diffraction revealed an in-plane epitaxial (isotropic) growth of Pt on MgO (Si). Their magnetic properties have been studied by vibrating sample magnetometry and Brillouin light scattering (BLS) in the Damon-Eshbach geometry. Vibrating sample magnetometry characterizations show that films grown on MgO are in-plane magnetized, while films deposited on Si are perpendicularly magnetized for CoFe thickness below 1.4 nm. The BLS measurements reveal a pronounced nonreciprocal spin waves propagation, which increases with decreasing CoFe thickness. This nonreciprocity was attributed to an interfacial Dzyaloshinskii-Moriya interaction (DMI) induced by Pt interface with CoFe. Moreover, the DMI sign has been found to depend on the stacks order: it is positive (negative) for CoFe/Pt (Pt/CoFe). The effective thickness dependence of the DMI effective constant shows two regimes due to the degradation of the interfaces as the CoFe thickness decreases. We thus show that the magnetic dead layer should be taken into account to precisely determine the surface DMI constant ${D}_{\mathrm{s}}$. Therefore, for the thickest samples, the surface DMI constants are nearly opposite: $\ensuremath{-}1.27$ and $1.32\phantom{\rule{0.16em}{0ex}}\mathrm{pJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$ for Pt/CoFe and its reversed system, respectively.

Co ultrathin films, of various thicknesses (0.8 nm ≤ tCo ≤ 2.5 nm), have been grown by sputtering on Si substrates, using Pt buffer layers and different capping layers (Cu, Ir, MgO and Pt). The x-ray diffraction revealed that our films have a (1 1 1) out-of-plane texture with various degrees of strains. Their magnetic properties have been studied by vibrating sample magnetometry (VSM) and Brillouin light scattering (BLS) in the Damon–Eshbach geometry. VSM characterizations revealed that films with Co thickness below (above) the spin reorientation transition thickness, which is capping layer dependent, are perpendicularly (in-plane) magnetized, suggesting the existence of an interface anisotropy. The surface anisotropy constant was found to be 1.42 ± 0.02 erg cm−2 and of 1.33 ± 0.02 erg cm−2 for the Pt/Co/Cu and Pt/Co/Ir samples, respectively, suggesting that it is due to the Pt/Co interface and that the top Co/Cu, Co/Pt or Co/Ir interfaces have a minor contribution. A lower value of 1.07 ± 0.02 erg cm−2 has been obtained for Pt/Co/MgO most probably due to over-oxidation of Co at the Co/MgO interface. The BLS measurements revealed a pronounced nonreciprocal spin waves propagation, due to the interfacial Dzyaloshinskii–Moriya interaction (iDMI) induced by Pt interface with Co, which increases with decreasing Co thickness. The magnetic dead layer has been taken into account to precisely determine the surface iDMI constant Ds estimated at −0.8 pJ m−1, −1.05 pJ m−1 and −0.95 pJ m−1, respectively for Pt/Co/Ir, Pt/Co/Cu and Pt/Co/MgO for sample thicknesses where a linear thickness dependence of the effective iDMI constant has been observed.

Co20Fe60B20/Pt systems with variable thicknesses of Co20Fe60B20 and of Pt have been sputtered and then annealed at various temperatures (Ta) up to 300 °C. Microstrip line ferromagnetic resonance (MS-FMR) has been used to investigate Co20Fe60B20 and Pt thickness dependencies of the magnetic damping enhancement due to the spin pumping. Using diffusion and ballistic models for spin pumping, the spin mixing conductance and the spin diffusion length have been deduced from the Co20Fe60B20 and the Pt thickness dependencies of the Gilbert damping parameter α of the Co20Fe60B20/Pt heterostructures, respectively. Within the ballistic simple model, both the spin mixing conductance at the CoFeB/Pt interface and the spin-diffusion length of Pt increase with the increasing annealing temperature and show a strong enhancement at 300 °C annealing temperature. In contrast, the spin mixing conductance, which increases with Ta, shows a different trend to the spin diffusion length when using the diffusion model. Moreover, MS-...

Zinc oxide with a hexagonal wurzite type structure is an unique material that exhibits semiconducting, piezoelectric and pyroelectric properties. These properties play a key role for applications in optoelectronic devices. In the present work Al-doped and undoped ZnO films were obtained by soft chemistry starting with zinc acetate dihydrate and Al(III) isopropoxide in absolute ethyl alcohol. Trietanolamine was used as chelating agent. The films were deposited by dip coating technique on the silicon substrate and thermally treated at 500?C for one hour. The morphological characteristics of the films were investigated by Atomic Force Microscopy (AFM). Optical constants, such as refractive index (n) and extinction coefficient (k), were established by Spectroellipsometry measurements. Electrical conductivity of the studied films was determined in the 20-500?C temperature range by 'the four point method'. The morphology of the films is influenced by the starting sol composition, as found from AFM. According to the ellipsometric spectral data, more porous and thinner films, with smaller refractive index were obtained in the case of Al-doped ZnO films as compared with ZnO films. Both ZnO and Al-doped ZnO films presented high electrical receptivity. .

The structural and chemical order are the most important parameters governing the physical properties of the Heusler compounds. Here, we give a comprehensive overview of the correlations between structural and chemical order, electronic transport (longitudinal and transverse) and magnetic (static and dynamic) properties of ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ Heusler alloy epitaxial thin films grown on MgO(001) single-crystal substrates. X-ray diffraction measurements indicated that depending on the annealing temperature the films show $B2$ or $L{2}_{1}$ chemical ordering. Longitudinal magnetoresistivity experiments revealed that for the best $L{2}_{1}$ ordered film, at temperatures bellow $125\phantom{\rule{4pt}{0ex}}\text{K}$, the magnon assisted electronic scattering is quenched indicating the appearance of half-metallicity. The presence of quantum correction in resistivity, whose strength is dependent on the structural ordering, was evidenced at low temperatures. Anomalous Hall experiments indicated that the intrinsic band structure contribution has an opposite sign and that is dominant over the extrinsic skew scattering mechanism. The presence of a small uniaxial magnetic anisotropy contribution superimposed on a larger biaxial one was evidenced via ferromagnetic resonance microstrip line measurements. The biaxial term is well correlated with chemical ordering, having a minimum value for the optimum $L{2}_{1}$ ordered film. The damping parameter was evaluated from ferromagnetic resonance linewidth measurements, and a coefficient as low as $1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ was found for the $L{2}_{1}$ phase.

Perpendicular magnetic anisotropy (PMA) is considered as one of the highly desirable properties of magnetic thin films for modern spintronic devices. In fact, the integration of materials with PMA reduces the critical current densities and enhances the thermal stability [1] in spin transfer torque based magnetic random access memories (STT-MRAM). Moreover, the large anisotropy values in such materials yields narrow domain walls making them good candidates for high-density STT-MRAM involving the propagation of magnetic domain walls. Co/Pt and Co/Pd mutilayers have been recognized many years ago as perpendicularly magnetized materials [2]. However, their application as electrodes in magnetic tunnel junctions (TMJ) and in giant magnetoresistance (GMR) devices has been limited by the reduced magnetoresitsance (TMR or GMR) values [2] and the high Gilbert damping parameter due to the spin-orbit coupling (SOC) of the Pt or Pd. Recently, strong PMA in ferromagnetic thin films (FM), Co, CoFe, and CoFeB when interfaced with an oxide, has been demonstrated [3-5] due to the hybridization of the O 2p and the FM (e.g. Fe) 3d orbitals, together with a degeneracy lift induced by SOC. Therefore, designing heterostructures presenting this interface PMA and incorporating FM that combines high spin polarisation and low Gilbert damping such as Co 2 FeAl (CFA) full Heusler alloy would be an attractive step towards building suitable materials for the above-mentioned spintronic applications.

Microstrip line ferromagnetic resonance (MS-FMR) has been used to investigate the dependence of the magnetic damping enhancement on the thickness of Co20Fe60B20 and Pt due to spin pumping. Samples with variable thicknesses of Co20Fe60B20 (Pt) are used to determine the spin mixing conductance (spin diffusion length) via the thickness dependence of the Gilbert damping parameter α of Co20Fe60B20/Pt heterostructures. The results obtained from the analysis of the MS-FMR measurements reveal that α increases linearly with the inverse thickness of Co20Fe60B20 for films capped with a 10 nm thick Pt layer, while the variation of α versus the Pt thickness of the 4 nm thick Co20Fe60B20 layer has an exponential behaviour. The experimental data was analysed using a ballistic or a diffusive spin transport model for spin pumping, which includes the effective spin mixing conductance of the CoFeB/Pt interface and the spin-diffusion length of Pt. The estimated values are 37.5 nm−2 (spin mixing conductance) and 1.7 nm when the ballistic transport model is used, and 56.75 nm−2 and 2.2 nm when the experimental data are analysed using a more realistic model based on a diffusive transport. Moreover, MS-FMR measurements reveal that the effective magnetization varies linearly with the Co20Fe60B20 inverse thickness due to the perpendicular interface anisotropy. This anisotropy, estimated to be 1.31 erg cm−2, reinforces the perpendicular magnetization easy axis.

The occurrence of both interlayer exchange coupling and perpendicular magnetic anisotropy is evidenced in Pt/Co/Ir/Co/Pt magnetron sputtered structures. We point out the effect of lattice strains on stabilizing the perpendicular magnetic anisotropy. The surface magnetic anisotropy constant is around 1.76 erg cm−2 and around 1.5 erg cm−2 for the Co layers, depending on their positioning within the stack. We demonstrate a relatively high interlayer exchange constant of −2.5 erg cm−2 at the first antiferromagnetic coupling maximum corresponding to an exchange field larger than 12 kOe. The interlayer exchange coupling shows remarkable annealing endurance being preserved for annealing temperatures up to 400 °C.

We have studied the magnetomechanical properties of thin films deposited on polyimide substrate. Particularly, we studied the effect of annealing in the accessible temperature range (0–375 °C) allowed by the polymer substrate. Complementary techniques have been used to characterize the elastic, magnetic and magnetoelastic properties of annealed samples (Brillouin light scattering and tensile tests combined with in situ ferromagnetic resonance). Below 200 °C, no significant evolutions of the properties have been found excepted the magnetic damping parameter. In contrast, above 200 °C, strong variations are observed (+15% for Young's modulus, for magnetostriction coefficient and +500% for the uniaxial magnetic anisotropy field). This is in correlation with the x-ray diffraction peak sharpening observed in the studied thin films. This is most probably due to exceeding of the glass transition temperature of the thin film. The complete data analysis allowed an estimation of the thermal stability of alloy thin films.

10 nm and 50 nm thick Co 2 FeAl (CFA) thin films have been deposited on thermally oxidized Si(001) substrates by magnetron sputtering using a Tantalum cap layer and were then ex-situ annealed at 415°C, 515°C and 615°C during 15 minutes in vacuum. X-rays diffraction indicates that films CFA are polycrystalline and exhibit an in-plane isotropy growth. Ferromagnetic resonance measurements, using a microstrip line (MS-FMR), reveal a huge interfacial perpendicular magnetic anisotropy and small in-plane uniaxial anisotropy both annealing temperature-dependent. The MS-FMR data also allow concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with annealing temperature. Finally, the FMR linewidth decreases with increasing annealing temperature due to the enhancement of the chemical order, and allow deriving a very low intrinsic damping parameter (1.3×10 −3 at 615°C).

The correlation between magnetic and structural properties of Co_{2} FeAl (CFA) thin films of different thickness (10 nm, Comment: 5 pages, 4 figures, submitted to J. Mag. Mag. Mat

In the present paper, we analyze the role of in situ grown BaZrO3 (BZO) inclusions in YBa2Cu3O7−x (YBCO) thin films prepared by chemical solution deposition using a low fluorine coating solution, on the field angle dependence of the critical current density, J c (𝜃), data using the vortex path model. In order to form a coherent picture on the BZO doping influence on the pinning properties of the YBCO matrix, detailed structural analyses performed by X-ray diffraction techniques and microstructural evaluation by transmission electron microscopy are also presented. The evaluation of different contributions to the overall, J c , permitted us to prove the effectiveness of the BZO inclusions acting as isotropic pinning centers, reflected in a uniform component of high relative value with respect to other components. For the studied 10 mol % BZO doping concentration, a threefold increase in the critical current density, J c , of the YBCO host is measured, in self-field at 77 K, corresponding to a value of J c =2.9MA/cm2, whereas a factor 10 is measured at 1 T (J c =0.35 MA/cm2).

Bending effect on the magnetic anisotropy in 20 nm Co$_{2}$FeAl Heusler thin film grown on Kapton\textregistered{} has been studied by ferromagnetic resonance and glued on curved sample carrier with various radii. The results reported in this letter show that the magnetic anisotropy is drastically changed in this system by bending the thin films. This effect is attributed to the interfacial strain transmission from the substrate to the film and to the magnetoelastic behavior of the Co$_{2}$FeAl film. Moreover two approaches to determine the in-plane magnetostriction coefficient of the film, leading to a value that is close to $\lambda^{CFA}=14\times10^{-6}$, have been proposed., Comment: 4 pages, 4 figures

Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have been deposited on MgO(001) substrates by magnetron sputtering and then capped by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA axis is normal to the substrate and that all the CFA films exhibit full epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$ phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer measurements show that, depending on the field orientation, one or two-step switchings occur. Moreover, the films present a quadratic MOKE signal increasing with the CFA thickness, due to the increasing chemical order. Ferromagnetic resonance, MOKE transverse bias initial inverse susceptibility and torque (TBIIST) measurements reveal that the in-plane anisotropy results from the superposition of a uniaxial and of a fourfold symmetry term. The fourfold anisotropy is in accord with the crystal structure of the samples and is correlated to the biaxial strain and to the chemical order present in the films. In addition, a large negative perpendicular uniaxial anisotropy is observed. Frequency and angular dependences of the FMR linewidth show two magnon scattering and mosaicity contributions, which depend on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found., 11 pages, 11 figures, to appear in Phys. Rev B

The ability of metallic nanostructures to support surface plasmon excitations is widely exploited nowadays for developing new technologies and applications in many fields, like communications, medicine or environment. It is known that the plasmonic response of a nanostructure is strongly dependent on its size and shape, and thus a fine control of these features is required for developing applications. In this paper uniaxial colloidal crystal arrays are prepared by convective self-assembly on DVD surfaces. These are then used as template/mask for metal film deposition, in order to obtain two original kinds of metallic nanostructures with controllable morphology: (i) linear arrays of metal half-shells (LAMHSs) and (ii) arrays of periodically serrated plasmonic strips (PSPSs). Angle-resolved optical transmittance measurements reveal the presence of several surface plasmon resonances, while polarized light transmission demonstrates the anisotropic plasmonic response of both LAMHSs and PSPSs. FDTD simulations support the experimental observations and help in the assignments of observed plasmon modes. The proposed linear metallic nanostructures can prove useful for the design of plasmonic components.

Magnetization switching by current induced spin–orbit torques (SOTs) in heavy metal/ferromagnetic metal/oxide structures is of great research interest due to its potential applications in the field of low power consumption spintronic devices. Here, we study the Slonczewski-like and the field-like SOT effective fields in β-W/Co2FeAl/MgO structures showing perpendicular magnetic anisotropy (PMA). We characterize the SOT effective fields using harmonic Hall voltage measurements and we point out the essential role of the planar Hall effect corrections. We estimate that for bulk β-W an effective spin Hall angle as large as 0.3 ± 0.03 and a spin diffusion length of 2.2 ± 0.3 nm. Moreover, we demonstrate SOT-induced magnetization switching for charge current densities of the order of 106 A cm−2.

In this paper a unique expression of the anisotropy field induced by any multiaxial stress state in a magnetic thin film and probed by ferromagnetic resonance is derived. This analytical development has been made using the uniaxial equivalent stress concept, for which correspondances between definitions given by different authors in the literature is found. The proposed model for the anisotropy field has been applied to thin films (25 nm) stressed both by piezoelectric actuation (non-equi-biaxial) or by bending tests (uniaxial) and measured with a broadband ferromagnetic resonance technique. The overall exprimental data can be easily plotted on a unique graph from which the magnetostriction coefficient has been estimated.

Magneto-stress coupling has been studied in Co20Fe60B20 thin films of varying thicknesses (10, 20 and 250 nm) deposited onto flexible substrate. It has been investigated by measuring the magnetic resonance under uniaxial (tensile or compressive) applied stresses in situ. The benchmark state, in terms of elastic and magnetic properties, was studied by combining Brillouin light scattering experiments and magnetic resonance experiments on flat samples. The deduced parameters are thickness-independent and close to the ones obtained using rigid substrates. A large uniaxial anisotropy proportional to the applied uniaxial stress is found, which is well fitted by considering an isotropic saturation magnetostriction coefficient. Finally, the angular dependence of the resonance field with in-plane biaxial stresses is probed and explained using a simple analytical model.

International audience; This paper presents our results regarding oxygen incorporation effects in epitaxial La(1-x)SrxMnO3 thin films, deposited on SrTiO3 (001) single crystal substrates, by annealing in different gas mixtures of argon and oxygen. A particular emphasis is placed on the correlation of structural properties with the magnetic properties of the films, Curie temperature, and coercive field. In this sense, we demonstrate that the evolution of the diffuse part of the ω-scans performed on the films are due to oxygen excess in the film lattice, which creates cationic vacancies within the films. Also, we show that two regimes of oxygen incorporation in the films exist, one in which the films evolve toward a single phase and oxygen stoichiometry is recovered, and a second one dominated by oxygen over-doping effects. In order to support our study, XPS measurements were performed, from which we have evaluated the Mn3+/Mn4+ ionic ratio

Our paper presents the study of exchange coupling between two ferromagnetic layers, separated by a non‐magnetic one. As a non‐magnetic spacer layer we have chosen a metal, ruthenium, and an insulator, magnesium oxide. Two types of structures were elaborated. One consists of a Co/Ru/Co multilayer, deposited by means of e‐beam evaporation, and the other of a Fe/MgO/Fe multilayer obtained through MBE. The morphological properties of the as deposited structures were determined by means of atomic force microscopy, while the study of the magnetic properties was carried out using vibrating sample magnetometry and magnetoresistance measurements. A maximum in the exchange coupling strength was obtained for a Ru thickness of 0.8nm and for an MgO layer of 0.6 nm, respectively. The utility of the coupled structure as an artificial antiferrimagnet was exploited in the development of two types of spin valves, one for each coupled multilayer, each one exhibiting good giant magnetoresistive response.

Microstripline ferromagnetic resonance technique has been used to study the indirect magnetoelectric coupling occurring in an artificial magnetoelectric heterostructure consisting of a magnetostrictive thin film cemented onto a piezoelectric actuator. Two different modes (sweep-field and sweep-frequency modes) of this technique have been employed to quantitatively probe the indirect magnetoelectric coupling and to observe a voltage induced magnetization rotation (of 90°). This latter has been validated by the experimental frequency variation of the uniform mode and by the amplitude of the sweep-frequency spectra.