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The effect of the stray field of Fe/Fe3O4 nanoparticles on the angular dependence of the microwave absorption derivative in CoFeB/Ta/CoFeB synthetic ferrimagnetic structures and CoFeB films with perpendicular anisotropy is analyzed, and its application for sensor technology is proposed. The effective field of the "platform-particles" system controlled by the magnetic dipole interaction of the CoFeB-Fe/Fe3O4 system decreased to zero in areas where the platform was magnetostatically coupled with nanoparticles. Micromagnetic modeling demonstrated the distribution of magnetization and resistance in local areas of CoFeB/Ta/CoFeB structures under the nanoparticles. The microwave absorption derivative can be used as an indicator of local magnetization switching of the giant magnetoresistance (GMR) structure under scattering fields of NPs or magnetically labeled cells. The limiting sensitivity of the detection method was 2.4 × 107 nanoparticles, which covered the spin-valve surface. We have proposed to combine the advantages of a GMR sensor with wireless technology of microwave reading of magnetoresistance for the detection of magnetically labeled cells.

The impact of plasmonic surface lattice resonances on the magneto-optical properties and energy absorption efficiency has been studied in arrays of [Co/Gd/Pt]

A method for subsurface visualization and characterization of hidden subsurface nano-structures based on Scanning Tuneling Microscopy/Spectroscopy (STM/STS) has been developed. The nano-objects buried under a metal surface up to several tens of nanometers can be visualized through the metal surface and characterized with STM without destroying the sample. This non-destructive method exploits quantum well (QW) states formed by partial electron confinement between the surface and buried nano-objects. The specificity of STM allows for nano-objects to be singled out and easily accessed. Then, their shape, size and burial depth can be determined by analyzing the spatial distribution and oscillatory behavior of the electron density at the surface of the sample. The proof of concept was demonstrated by fabricating argon nanoclusters embedded into a single-crystalline Cu matrix. Taking advantage of the specific electronic band structure Cu and inner electron focusing, we experimentally demonstrated that noble-gas nanoclusters of several nanometers large buried as deep as 80 nm can be detected, characterized and imaged. The ultime depth of this ability is estimated as 110 nm. This approach using QW states paves the way for an enhanced 3D characterization of nanostructures hidden well below a metallic surface., Accepted in Nanoscale Horizons Nanoscale Horiz., 2023, Accepted Manuscript https://doi-org.bases-doc.univ-lorraine.fr/10.1039/D3NH00052D

National audience; Portée par l’internet des objets et l’intelligence artificielle, la quantité de données générées et stockées augmente de manière exponentielle. A l’horizon 2030, 20 % de l’électricité mondiale sera utilisée pour le stockage et la gestion des données. Une très large majorité des données est stockée sur des surfaces magnétiques. Nous démontrons que nous pouvons retourner l’aimantation d’une couche ferromagnétique, donc écrire de l’information, grâce à un seul pulse laser femto-seconde.

International audience; Terahertz (THz) emission from magnetic films has recently become an important characterization tool of spintronic properties, particularly since no patterning is required. One such property of interest is the spin-current attenuation length. When separating a magnetic film from a spin-to-charge converter with a light metal, the emitted intensity reduces almost exponentially with the thickness of the spacer. However, the extracted characteristic length is more than an order of magnitude smaller than the spin diffusion length measured in equilibrium. In this work, we experimentally and theoretically demonstrate that most of the observed decay in the THz emission is of optical (THz) origin. We are able to estimate a spin current attenuation length for Cu of ∼50 nm in much closer agreement with spin diffusion length measurements. We conclude that THz emission remains a powerful characterization technique, but due to the high number of intricate conversion mechanisms, and most importantly, due to the high sensitivity to changes in the optical properties, extracting absolute numbers for spintronic phenomena remains extremely challenging.

We use ab initio real-time time-dependent density functional theory to investigate the effect of optical and extreme ultraviolet (XUV) circularly polarized femtosecond pulses on the magnetization dynamics of ferromagnetic materials. We demonstrate that the light induces a helicity-dependent reduction of the magnitude of the magnetization. In the XUV regime, where the 3p semicore states are involved, a larger helicity dependence persisting even after the passage of light is exhibited. Finally, we were able to separate the part of the helicity-dependent dynamics due to the absorption from the part due to the inverse Faraday effect. Doing so, we show that the former has, overall, a greater impact on the magnetization than the latter, especially after the pulse and in the XUV regime. This work hints at the yet experimentally unexplored territory of the XUV light-induced helicity-dependent dynamics, which, according to our prediction, could magnify the helicity-dependent dynamics already exhibited in the optical regime.

International audience; All optical switching (AOS) of magnetization exhibits a high potential for ultrafast and energy-efficient memory applications. Many works have been carried out in the area of AOS, including its observation in a wide variety of ferromagnetic or ferrimagnetic materials, and the exploration of the parameters for the achievements of AOS such as the laser fluence and helicity, and duration of laser pulses. A large majority of all optical helicity-independent single-shot switching (AO-HIS) has been observed in Gd-based rare-earth transition-metal ferrimagnets. It is then necessary to explore the unique role of Gd in AO-HIS mechanism, compared with other rare-earth elements. Here, we engineered Gd 1−x−y Tb y Co x alloys and investigated the influence of the Tb concentration on the magnetization dynamics via static Kerr microscope and time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. The ultrafast demagnetization time at low fluence is found to be independent of Tb concentration, while both the range of laser fluence and pulse duration allowing for AO-HIS becomes narrower with increasing the Tb concentration. The TR-MOKE signal K / K_sat ∼ 10 ps after the laser pulse excitation decreases with increasing either the Tb concentration or the pulse duration. The fact that AO-HIS is prohibited by increasing the Tb content is explained by considering a larger damping for Tb than Gd in atomistic simulations. Our results are well explained by the fact that angular momentum can be transferred from Gd to Co resulting in the magnetization switching, whereas for Tb it is dissipated through the lattice due to the large spin-orbit coupling, instead of being transferred between Tb and Co.

The development of approaches that can efficiently control the magnetization of magnetic materials is central to the creation of fast and low-power spintronic devices. Spin transfer torque can be used to electrically manipulate magnetic order in devices, but is typically limited to nanosecond timescales. Alternatively, spin–orbit torque can be employed, and switching with current pulses down to ~200 ps has been demonstrated. However, the upper limit to magnetization switching speed remains unestablished. Here, we show that photoconductive switches can be used to apply 6-ps-wide electrical pulses and deterministically switch the out-of-plane magnetization of a common thin cobalt film via spin–orbit torque. We probe the ultrafast magnetization dynamics due to spin–orbit torques with sub-picosecond resolution using the time-resolved magneto-optical Kerr effect (MOKE). We also estimate that the magnetization switching consumes less than 50 pJ in micrometre-sized devices. The magnetization of a cobalt thin film can be reversed by spin–orbit torques using picosecond electrical pulses that are generated by photoconductive switches.

The magnetization reversal of the MgO/CoFeB/Ta/CoFeB/MgO/Ta/GaAs heterostructures and the ultrathin MgO/CoFeB/MgO/Ta/GaAs films with a perpendicular anisotropy in the magnetic field of clusters of Fe/Fe3O4 nanoparticles is experimentally observed. The stray magnetic field of Fe/Fe3O4 nanoparticles increases the field of switching the magnetization of spin valves and monolayer platforms. The size of the magnetization reversal region of the ferromagnetic platform under Fe/Fe3O4 nanoparticles as a function of the cluster size was determined by atomic force and magnetic force microscopy. The size of the magnetization reversal region is found to be larger than the particle cluster size, which is caused by the stray field of a cluster of Fe/Fe3O4 nanoparticles. The local magnetization orientations in the CoFeB layers under clusters of nanoparticles and the magnetization reversal region diameter are determined as functions of the magnetic moment and the size of the cluster using micromagnetic simulation.

The purpose of the work is to find the dependence of growth rate of magnetization centers of various types on their surrounding by other nucleation centers in a synthetic Pt/Co/Ir/Co/Pt ferrimagnet with perpendicular magnetic anisotropy. The following four types of nucleation centers exist in a sample with two ferromagnetic layers of different thicknesses: P+ centers correspond to the regions where the magnetizations of the thick and thin Co layers are directed along an applied field (↑↑); P– centers are the regions where the magnetizations of the layers are opposite to an applied field (↓↓); and AP+ and AP– centers correspond to the regions where the magnetizations of the thick and thin Co layers are opposite to each other and the total magnetic moment is along (↑↓) or opposite to (↓↑) an applied field, respectively. P– nucleation centers are found to be surrounded by AP+ regions in any field and exhibit a monotonic field dependence of their boundary. The field dependence of the growth rate of AP– nucleation centers is nonmonotonic since, as the field increases, they are surrounded by AP+ nucleation centers, AP+ and P– regions, and only P– nucleation centers in strong fields.

International audience; Irradiation of the heterostructure glass/Ta/Pt/GdFeCo/IrMn/Pt by 50 fs ultra-short laser pulses causes local thinning of the film down to~12-30 nm depth. These pits are distinguished by Atomic Force Microscopy (AFM), while their stray magnetic fields were detected by Magnetic Force Microscopy (MFM). The crater was formed due to layer-by-layer evaporation of the material. No sign of melting was found in the vicinity of the crater at subthreshold laser fluence below 12-15 mJ/cm 2 , but exceeding of the threshold caused destruction of the layers. Energy-dispersive X-ray spectroscopy (EDX) revealed depletion of Gd, Fe and Co, responsible for magnetic properties of the subthreshold crater. The amplitude of the local MOKE signal decreased down to 1.7 times in the irradiated area, while thinning of the ferromagnetic layer was 1.1 times. No proportional change of magneti-zation was caused by bias effect of IrMn layer. Decreased elastic modulus was found inside the subthreshold crater in the irradiated areas. Laser engineering of the surface of GdFeCo thin films opens the way for local control of energy balance between magnetic anisotropy, exchange coupling and Zeeman energy and creation of separated sectors for capture, storage and analysis of the ferromagnetic nanoparticles.

A 5 nm thick ferrimagnetic film made of amorphous rare-earth transition-metal alloys Gdx(Fe90Co10)1-x was grown by physical vapor deposition. Its magnetic properties (coercivity, perpendicular magnetic anisotropy, and compensation composition at room temperature) were investigated for various buffer and capping layers in contact with a ferrimagnetic thin film. While Gdx(Fe90Co10)1-x appears to be amorphous for all the samples, it appears that (111) textured Cu is the best material to promote perpendicular magnetization. The large compensation composition change as a function of the magnetic film interface at room temperature is analyzed in terms of polarizability of the surrounding buffer and capping materials.

Here, we study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on magnetic nuclei expansion in Pt/Co/Ir/Co/Pt perpendicular synthetic ferrimagnets. Magnetization reversal is explored as a response to the DMI, affecting the expansion of the magnetic nuclei. We report a nontrivial inverted dependence of the velocity of the double domain wall on the in-plane (IP) magnetic field. This effect is due to competition of the DMI contributions, resulting in effective fields of different signs in the two Co layers. We report a macroscopic manifestation of the DMI as magnetization reversal accelerated by the applied IP magnetic field. Accelerated magnetic relaxation is provided by the DMI-induced ellipticity of the magnetic nuclei, the spreading of which is accompanied by an enhanced number of nuclei contacts in comparison with round nuclei in the absence of an IP field. The obtained results clarify how the DMI contributes to macroscopic magnetic relaxation in the presence of the interlayer Heisenberg exchange interaction in synthetic ferrimagnets with perpendicular anisotropy.

We present analysis of the effect of Dzyaloshinskii–Moriya interaction (DMI) on spin wave nonreciprocity and bubble expansion asymmetry in Pt/Co/Ir/Co/Pt synthetic ferrimagnets with perpendicular magnetic anisotropy. We propose analysis of the DMI by Brillouin light scattering technique (BLS) and Kerr microscopy (MOKE) in the presence of interlayer exchange coupling strongly changing spin wave dispersion law and field dependences of domain wall velocity in comparison with those observed earlier in Ir/Co/Pt structures with a single Co layer. We have determined DMI values of each Co layer from unusually inverted dependence of velocity of the domain wall on in-plane magnetic field. Opposite signs of effective fields and DMI fields in the two Co layers invert field dependence of the domain wall velocity. DMI energy determined from BLS is higher than values, determined by bubble expansion.

International audience; We review the phenomenology of light-induced ultrafast magnetization dynamics, with emphasis on metallic compounds. The interaction of femtosecond laser pulses with magnetic thin films induces a wide range of out of equilibrium phenomena, leading to an ultrafast demagnetization, and a subsequent magnetization dynamics. The latter can lead to a deterministic reversal of the magnetization or allow for the controlled motion of domain walls. Those light-induced magnetization manipulations have potential application for ultrafast and energy efficient spintronic. The review summarizes experimental results and theoretical approaches on demagnetization and the all-optical helicity-dependent switching of the magnetization, whose underlying mechanism(s) are still heavily debated, even after 25 years of intensive research.

Switching of perpendicular magnetization via spin–orbit torque (SOT) is of particular interest in the development of non-volatile magnetic random access memory (MRAM) devices. We studied current-induced magnetization switching of Ir/GdFeCo/Cu/Pt heterostructures in a Hall cross geometry as a function of the in-plane applied magnetic field. Remarkably, magnetization switching is observed at zero applied field. This is shown to result from the competition between SOT, the Oersted field generated by the charge current, and the material's coercivity. Our results show a means of achieving zero-field switching that can impact the design of future spintronics devices, such as SOT-MRAM.

Ultrafast magnetization switching induced by a single femtosecond laser pulse, under no applied magnetic field has attracted a lot of attention in the last 10 years because of its high potential for low-energy and ultrafast memory applications. Single-pulse helicity-independent switching has mostly been demonstrated for $\mathrm{Gd}$-based materials. It is now necessary to optimize the pulse duration and the energy needed to switch a $\mathrm{Gd}$-$\mathrm{Fe}$-$\mathrm{Co}$ magnet depending on the alloy thickness and composition. Here we experimentally report state diagrams showing the magnetic state obtained after one single pulse depending on the laser pulse duration and fluence for various $\mathrm{Gd}$-$\mathrm{Fe}$-$\mathrm{Co}$ thin films with different compositions and thicknesses. We demonstrate that these state diagrams share similar characteristics: the fluence window for switching narrows for longer pulse duration and for the considered pulse-duration range the critical fluence for single-pulse switching increases linearly as a function of the pulse duration while the critical fluence required for creating a multidomain state remains almost constant. Calculations based on the atomistic spin model qualitatively reproduce the experimental state diagrams and their evolution. By studying the effect of the composition and the thickness on the state diagram, we demonstrate that the best energy efficiency and the longest pulse duration for switching are obtained for composition around the magnetic compensation.

The Dzyaloshinskii-Moriya interaction (DMI) in magnetic systems stabilizes spin textures with preferred chirality, applicable to next-generation memory and computing architectures. In perpendicularly magnetized heavy-metal/ferromagnet films, the interfacial DMI originating from structural inversion asymmetry and strong spin-orbit coupling favors chiral N\'eel-type domain walls (DWs) whose energetics and mobility remain at issue. Here, we characterize a new effect in which domains expand unidirectionally in response to a combination of out-of-plane and in-plane magnetic fields, with the growth direction controlled by the in-plane field strength. These growth directionalities and symmetries with applied fields cannot be understood from static treatments alone. We theoretically demonstrate that perpendicular field torques stabilize steady-state magnetization profiles highly asymmetric in elastic energy, resulting in a dynamic symmetry breaking consistent with the experimental findings. This phenomenon sheds light on the mechanisms governing the dynamics of N\'eel-type DWs and expands the utility of field-driven DW motion to probe and control chiral DWs., Comment: 20 pages, 4 figures, 10 supplementary figures

International audience; In this paper, we investigate the magnetic, optical, and lattice responses of a Pt/Cu/Bi 1 Y 2 Fe 5 O 12 /Gd 3 Ga 5 O 12 heterostructure to femtosecond laser excitation of the opaque Pt/Cu metallic bilayer. The electronic excitation generates coherent and incoherent phonons, which trigger high-frequency standing spin waves (SWs) in the dielectric Bi 1 Y 2 Fe 5 O 12 layer via a phonon-induced change of magnetic anisotropy. We find that the incoherent phonons (heat) can induce a fast (1000 ps) decrease of the magnetic order by different spin-phonon interaction scenarios. These results open perspectives for generating high-frequency SWs in buried magnetic garnets.

Spintronics exploits spin-orbit coupling (SOC) to generate spin currents, spin torques, and, in the absence of inversion symmetry, Rashba, and Dzyaloshinskii-Moriya interactions (DMI). The widely used magnetic materials, based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this shortcoming, the common practice has been to utilize the large SOC of nonmagnetic layers of 5d heavy metals (HMs), such as Pt, to generate spin currents by Spin Hall Effect (SHE) and, in turn, exert spin torques on the magnetic layers. Here, we introduce a new class of material architectures, excluding nonmagnetic 5d HMs, for high-performance spintronics operations. We demonstrate very strong current-induced torques exerted on single GdFeCo layers due to the combination of large SOC of the Gd 5d states, and inversion symmetry breaking mainly engineered by interfaces. These "self-torques" are enhanced around the magnetization compensation temperature (close to room temperature) and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In other measurements, we determine the very large emission of spin current from GdFeCo. This material platform opens new perspectives to exert "self-torques" on single magnetic layers as well as to generate spin currents from a magnetic layer., Comment: 26 pages, 4 figures plus 5 pages of sup. information

We present an experimental investigation of the magnetic and magnetocaloric properties of sputtered epitaxial and amorphous Tb thin films. We grew epitaxial Nb (50-nm)/Tb (100-nm) bilayer thin films on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(11\overline{2}0$) substrate using DC magnetron sputtering at high temperature, with excellent crystalline quality of the hcp Tb(0001) layer. While the amorphous Tb thin film exhibits more isotropic magnetocaloric properties, we show that the epitaxial Tb thin film displays large anisotropic magnetocaloric properties, with a large maximum magnetic entropy change of $6.27\phantom{\rule{0.28em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at the N\'eel temperature as well as a large relative cooling power of $225\phantom{\rule{0.28em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$ with a magnetic field change $\mathrm{\ensuremath{\Delta}}H=20\phantom{\rule{0.28em}{0ex}}\mathrm{kOe}$ applied along the in-plane direction. These large and anisotropic magnetocaloric properties are much larger than those measured for the amorphous Tb thin film, or previously reported for Tb-based thin-film structures. Our findings highlight the opportunities for growing epitaxial rare-earth thin films using sputtering techniques and demonstrate the importance of crystallographic control on the magnetocaloric effect in Tb thin films.

International audience; Since it was recently demonstrated in a spin-valve structure, magnetization reversal of a ferromagnetic layer using a single ultrashort optical pulse has attracted attention for future ultrafast and energy-efficient magnetic storage or memory devices. However, the mechanism and the role of the magnetic properties of the ferromagnet as well as the time scale of the magnetization switching are not understood. Here, we investigate single-shot all-optical magnetization switching in a GdFeCo/Cu/[Co x Ni 1−x /Pt] spinvalve structure. We demonstrate that the threshold fluence for switching both the GdFeCo and the ferromagnetic layer depends on the laser pulse duration and the thickness and the Curie temperature of the ferromagnetic layer. We are able to explain most of the experimental results using a phenomenological model. This work provides a way to engineer ferromagnetic materials for energy efficient single-shot all-optical magnetization switching.

Magnetocaloric effect (MCE) in an antiferromagnetic holmium (Ho) film is studied near the spin reorientation temperatures. A series of magnetization isotherms from 60 to 150 K around the N\'eel temperature, ${T}_{N}\ensuremath{\approx}130\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ were recorded for both in-plane and out-of-plane magnetic field orientations. A change in entropy, $\mathrm{\ensuremath{\Delta}}{S}_{M}$ of $\text{--}5\phantom{\rule{0.28em}{0ex}}\mathrm{J}/\mathrm{kg}\mathrm{K}$ was found near ${T}_{N}$ for an in-plane field orientation. A large change in $\mathrm{\ensuremath{\Delta}}{S}_{M}$ of \ensuremath{-}11.8 J/kg K due to a fan-helix spin transition at $T=90\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is observed for an in-plane field orientation. Spin transition at both ${T}_{N}$ and at the fan-helix transition exhibit larger MCE in the in-plane field orientations in comparison with the perpendicular orientation. The value of the refrigerant capacity extracted from the temperature dependence of $\mathrm{\ensuremath{\Delta}}{S}_{M}(T)$ is found to be larger for the ``in- plane'' orientation by a factor of two.

International audience; Current induced magnetization switching is of particular interest to develop non-volatile magnetic memories (MRAM). We studied spinorbit torque (SOT) switching in a Pt/ferromagnet/antiferromagnet Pt/[Co/Ni]2/PtMn Hall cross. For the as-deposited sample, which showed no exchange bias effect, SOT switching is observed only under an in-plane applied field. In this case, when the in-plane applied field tends to zero, the current switching required diverges and the Hall voltage signal generated by the switching tends to zero. However, the same sample is annealed perpendicular to the plane and then in an in-plane applied field, which demonstrated not only square Hall voltage vs current hysteresis loops but also a moderate switching current in zero magnetic field. This procedure induces an out-of-plane exchange bias with strengthened perpendicular magnetic anisotropy and an in-plane exchange bias, which induces zero field SOT switching. The study of the SOT switching for both annealing procedures as a function of the injected current and the in-plane field is shown. These results could impact the design of future spintronics devices such as SOT-MRAM.

We report the generation of skyrmions under the combined influence of applied perpendicular magnetic fields and electrical currents in Pt/Co/Os/Pt thin films. Under no electrical current, skyrmions are found to nucleate at specific defect sites distributed throughout the film and remain pinned at these sites for small dc electrical currents $(l0.05\mathrm{MA}/\mathrm{c}{\mathrm{m}}^{2})$ . For larger currents $(l0.05\mathrm{MA}/\mathrm{c}{\mathrm{m}}^{2})$, skyrmions can either move or elongate in the direction of the current flow to form stripe domains. We further observed the current-induced generation of skyrmions through two specific processes: (i) stripe domains depinning from defect sites and collapsing into skyrmions, or (ii) skyrmions breaking off from pinned stripes; the rate of these stripe-to-skyrmion creation phenomena is proportional to the applied current density. Additionally, we observe a sudden increase in the skyrmion population immediately after the applied current is removed----a behavior attributed to stripe domains previously elongated by the electrical current collapsing back into skyrmions.

Summary Modulation of electronic properties in spintronic interfaces (spinterfaces) can give rise to the optimization and even emergence of abundant spintronic effects. However, a proof-of-concept demonstration of such a strategy has rarely been achieved. In this paper, we study the interlayer exchange coupling effect in a synthetic magnetic multilayer system [Pt/Co]2/VO2/[Co/Pt]2, where atomically thin phase-change material VO2 is adopted as a spinterface with reversible metal-to-insulator transition. Repeatable switching from antiferromagnetic coupling through insulating spinterface to ferromagnetic coupling through metallic spinterface is observed in this multilayer system. Further analyses indicate that such an evolution originates from two distinct coupling mechanisms of spin-dependent tunneling and Rudermann-Kittel-Kasuya-Yosida interaction determined by the electronic states of VO2. As an experimental demonstration of VO2-tailored interlayer exchange coupling effect, this work highlights the great potential of spinterface as a magic building block in beyond-CMOS electronic devices.

New methods to induce magnetization switching in a thin ferromagnetic material using femtosecond laser pulses without the assistance of an applied external magnetic field have recently attracted a lot of interest. It has been shown that by optically triggering the reversal of the magnetization in a GdFeCo layer, the magnetization of a nearby ferromagnetic thin film can also be reversed via spin currents originating in the GdFeCo layer. Here, using a similar structure, it is shown that the magnetization reversal of the GdFeCo is not required in order to reverse the magnetization of the ferromagnetic thin film. This switching is attributed to the ultrafast spin current and can be generated by the GdFeCo demagnetization. A larger energy efficiency of the ferromagnetic layer single pulse switching is obtained for a GdFeCo with a larger Gd concentration. Those ultrafast and energy efficient switchings observed in such spintronic devices open a new path toward ultrafast and energy efficient magnetic memories., In GdFeCo/Cu/[Co/Pt] spin valve, the ultrafast demagnetization of the ferrimagnetic GdFeCo alloy, generated by a single femtosecond laser pulse, is shown to generate enough spin current to switch the magnetization of the ferromagnetic Co/Pt multilayer. By increasing the Gd concentration, the Co/Pt switching is found to be more energy efficient.

et al., Spintronic devices exploit the spin, as well as the charge, of electrons and could bring new capabilities to the microelectronics industry. However, in order for spintronic devices to meet the ever-increasing demands of the industry, innovation in terms of materials, processes and circuits are required. Here, we review recent developments in spintronics that could soon have an impact on the microelectronics and information technology industry. We highlight and explore four key areas: magnetic memories, magnetic sensors, radio-frequency and microwave devices, and logic and non-Boolean devices. We also discuss the challenges—at both the device and the system level—that need be addressed in order to integrate spintronic materials and functionalities into mainstream microelectronic platforms.

International audience; Spin-transfer-driven oscillations of a transverse domain wall confined to a perpendicular spin-valve structure are investigated using a one-dimensional model. The stack consists of a polarizer, nonmagnetic spacer, soft free layer, and pinned magnetic layer. It is found that the domain-wall oscillation frequency is a nonmonotonic, highly asymmetrical function of applied electric current, showing a strong dependence on the current direction and the relative strengths of the interfacial and bulk spin-transfer torques. Micromagnetic analysis reveals that the surprising and atypical oscillator response is due to an interplay between the interfacial spin-transfer torque, the bulk spin-transfer torque, the exchange torque, and the damping torque. The underlying physical and material responses are examined, including the important role of the domain-wall twist. The competitions between the involved torques under different operating conditions suggest that the oscillator could serve as a model system to investigate magnetic and spintronic phenomena at the nanoscale. The observed current-dependent twisting of the free-layer magnetization about the axis of precession may further be found interesting for investigations of the interaction between spin-polarized current and chiral spin structures.

We have measured the hot-electron induced demagnetization of a [Co/Pt]2 multilayer in M(x nm)/Cu(100 nm)/[Co(0.6 nm)/Pt(1.1 nm)]2 samples depending on the nature of the capping layer M and its thickness x. We found out that a Pt layer is more efficient than [Co/Pt]X, Cu or MgO layers in converting IR photon pulses into hot-electron pulses at a given laser power. We also found out that the maximum relative demagnetization amplitude is reached for M(x) = Pt (7 nm). Our experimental results show qualitative agreement with numerical simulations based on the superdiffusive spin transport model. We concluded that the maximum relative demagnetization amplitude, which corresponds to the highest photon conversion into hot-electrons, is an interplay between the IR penetration depth and the hot-electron inelastic mean free path within the capping layer., Comment: 10 pages, 3 figures

Fe/Fe3O4 nanoparticles have been deposited on the surfaces of ultrathin CoFeB film and CoFeB/Ta/CoFeB hetero-structure to be detected due to the stray field generated by one particle or a cluster of particles. Exchange biased Fe/Fe3O4 core-shell nanoparticles have been used to stabilize the particles magnetization. Comparison between the Atomic Force and Magnetic Force Microscope images and subtraction of corresponding phase contrasts allows visualization of the film magnetization affected by the particles. Spectra of Ferromagnetic Resonance of the ultrathin films with deposited particles allow one to estimate particle/film dipolar interaction. The results will be useful for the development of lab-on-chip sensors of magnetically labeled cells. Estimation of particles number by magnetic response of the CoFeB heterostructure is demonstrated.

International audience; Optical methods for magnetism manipulation have been considered as a promising strategy for ultralow-power and ultrahigh-speed data storage and processing, which have become an emerging field of spintronics. However, a widely applicable and efficient method has rarely been demonstrated. Here, the strongly correlated electron material vanadium dioxide (VO 2) is used to realize the optically induced phase change for control of the magnetism in NiFe. The NiFe/VO 2 bilayer heterostructure features appreciable modulations of electrical conductivity (32%), coercivity (37.5%), and magnetic anisotropy (25%). Further analyses indicate that interfacial strain coupling plays a crucial role in the magnetic modulation. Utilizing this heterostructure, which can respond to both optical and magnetic stimuli, a phase change controlled anisotropic mag-netoresistance (AMR) device is fabricated, and reconfigurable Boolean logics are implemented. As a demonstration of phase change spintronics, this work may pave the way for next-generation opto-electronics in the post-Moore era.

Iridium is a very promising material for spintronic applications due to its interesting magnetic properties such as large RKKY exchange coupling as well as its large spin-orbit coupling value. Ir is for instance used as a spacer layer for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However, only a few studies of the spintronic parameters of this material have been reported. In this paper, we present inverse spin Hall effect - spin pumping ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the values of the effective spin Hall angle, the spin diffusion length within iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to have reliable results, we performed the same experiments on CoFeB/Pt bilayers, which behavior is well known due to numerous reported studies. Our experimental results show that the spin diffusion length within iridium is 1.3 nm for resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow \downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle of iridium has the same sign than the one of platinum and is evaluated at 26% of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt and 2% for Ir. These relevant parameters shall be useful to consider Ir in new concepts and devices combining spin-orbit torque and spin-transfer torque., Comment: 8 pages, 4 figures

International audience; Recently, a reversible and a giant rotating magnetocaloric effect has been pointed out in the multiferroic TbMn 2 O 5 single crystal, opening the way for new designs of low-temperature magnetic cooling. In this paper, we report a preliminary theoretical work with the aim of enlarging our understanding on the electronic, magnetic and accordingly magnetocaloric features of the TbMn 2 O 5 compound. Particularly, the TbMn 2 O 5 magnetic anisotropy is analyzed in terms of X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS) spectra.

Engineering of magnetic materials for developing better spintronic applications relies on the control of two key parameters: the spin polarization and the Gilbert damping, responsible for the spin angular momentum dissipation. Both of them are expected to affect the ultrafast magnetization dynamics occurring on the femtosecond timescale. Here, engineered Co

Reducing energy dissipation while increasing speed in computation and memory is a long-standing challenge for spintronics research. In the last 20 years, femtosecond lasers have emerged as a tool to control the magnetization in specific magnetic materials at the picosecond timescale. However, the use of ultrafast optics in integrated circuits and memories would require a major paradigm shift. An ultrafast electrical control of the magnetization is far preferable for integrated systems. Here we demonstrate reliable and deterministic control of the out-of-plane magnetization of a 1 nm-thick Co layer with single 6 ps-wide electrical pulses that induce spin-orbit torques on the magnetization. We can monitor the ultrafast magnetization dynamics due to the spin-orbit torques on sub-picosecond timescales, thus far accessible only by numerical simulations. Due to the short duration of our pulses, we enter a counter-intuitive regime of switching where heat dissipation assists the reversal. Moreover, we estimate a low energy cost to switch the magnetization, projecting to below 1fJ for a (20 nm)^3 cell. These experiments prove that spintronic phenomena can be exploited on picosecond time-scales for full magnetic control and should launch a new regime of ultrafast spin torque studies and applications., Includes article + supplementary information. Latest version uses full name of the first author. Nature Electronics (2020)