arXiv subjects

Abdelmadjid Anane

Publications and source records attributed to Abdelmadjid Anane.

30 records · Page 2Linked to original sources

arXiv2017

Electrical properties of single crystal Yttrium Iron Garnet ultra-thin films at high temperatures

We report a study on the electrical properties of 19 nm thick Yttrium Iron Garnet (YIG) films grown by liquid phase epitaxy. The electrical conductivity and Hall coefficient are measured in the high temperature range [300,400]~K using a Van der Pauw four-point probe technique. We find that the electrical resistivity decreases exponentially with increasing temperature following an activated behavior corresponding to a band-gap of $E_g\approx 2$ eV, indicating that epitaxial YIG ultra-thin films behave as large gap semiconductor, and not as electrical insulator. The resistivity drops to about $5\times 10^3$~$Ω\cdot \text{cm}$ at $T=400$ K. We also infer the Hall mobility, which is found to be positive ($p$-type) at 5 cm$^2$/(V$\cdot$sec) and about independent of temperature. We discuss the consequence for non-local transport experiments performed on YIG at room temperature. These electrical properties are responsible for an offset voltage (independent of the in-plane field direction) whose amplitude, odd in current, grows exponentially with current due to Joule heating. These electrical properties also induce a sensitivity to the perpendicular component of the magnetic field through the Hall effect. In our lateral device, a thermoelectric offset voltage is produced by a temperature gradient along the wire direction proportional to the perpendicular component of the magnetic field (Righi-Leduc effects).

cond-mat.mtrl-sci↗

arXiv2017

Spin conductance of YIG thin films driven from thermal to subthermal magnons regime by large spin-orbit torque

We report a study on spin conductance in ultra-thin films of Yttrium Iron Garnet (YIG), where spin transport is provided by propagating spin waves, that are generated and detected by direct and inverse spin Hall effects in two Pt wires deposited on top. While at low current the spin conductance is dominated by transport of thermal magnons, at high current, the spin conductance is dominated by low-damping non-equilibrium magnons thermalized near the spectral bottom by magnon-magnon interaction, with consequent a sensitivity to the applied magnetic field and a longer decay length. This picture is supported by microfocus Brillouin Light Scattering spectroscopy.

cond-mat.mtrl-sci↗

arXiv2017

Chirality-mediated bistability and strong frequency downshifting of the gyrotropic resonance of a dynamically de-stiffened magnetic vortex

We demonstrate an enhanced, bidirectional, in-plane magnetic field tuning of the gyrotropic resonance frequency of a magnetic vortex within a disk by introducing a flat edge. When the core is in its vicinity, the flat edge locally reduces the core's directional dynamic stiffness for movement parallel to the edge. This strongly reduces the net dynamic core stiffness, leading to the gyrotropic frequency being significantly less than when the core is centered (or located near the round edge). This leads to the measurable range of gyrotropic frequencies being more than doubled and also results in a clear chirality-mediated bistability of the gyrotropic resonance frequency due to what is effectively a chirality-dependence of the core's confining potential.

cond-mat.mes-hall↗

arXiv2016

Spin to charge conversion in MoS$_{2}$ monolayer with spin pumping

Layered transition-metal dichalcogenides (TMDs) family are gaining increasing importance due to their unique electronic band structures, promising interplay among light, valley (pseudospin), charge and spin degrees of freedom. They possess large intrinsic spin-orbit interaction which make them most relevant for the emerging field of spin-orbitronics. Here we report on the conversion of spin current to charge current in MoS2 monolayer. Using spin pumping from a ferromagnetic layer (10 nm of cobalt) we find that the spin to charge conversion is highly efficient. Analysis in the frame of the inverse Rashba-Edelstein (RE) effect yields a RE length in excess of 4 nm at room temperature. Furthermore, owing to the semiconducting nature of MoS$_{2}$, it is found that back-gating allows electrical field control of the spin-relaxation rate of the MoS$_{2}$-metallic stack.

cond-mat.mes-hall↗

arXiv2016

Electrical measurement of magnetic-field-impeded polarity switching of a ferromagnetic vortex core

Vortex core polarity switching in NiFe disks has been evidenced using an all-electrical rectification scheme. Both simulation and experiments yield a consistent loss of the rectified signal when driving the core at high powers near its gyrotropic resonant frequency. The frequency range over which the loss occurs grows and shifts with increasing signal power, consistent with non-linear core dynamics and periodic switching of the core polarity induced by the core attaining its critical velocity. We demonstrate that core polarity switching can be impeded by displacing the core towards the disk's edge where an increased core stiffness reduces the maximum attainable core velocity.

cond-mat.mes-hall↗

arXiv2015

Resonant translational, breathing and twisting modes of pinned transverse magnetic domain walls

We study translational, breathing and twisting resonant modes of transverse magnetic domain walls pinned at notches in ferromagnetic nanostrips. We demonstrate that a mode's sensitivity to notches depends strongly on the characteristics of that particular resonance. For example, the frequencies of modes involving lateral motion of the wall are the ones which are most sensitive to changes in the notch intrusion depth (especially at the narrower, more strongly confined end of the domain wall). In contrast, the breathing mode, whose dynamics are concentrated away from the notches is relatively insensitive to changes in the notches' sizes. We also demonstrate a sharp drop in the translational mode's frequency towards zero when approaching depinning which is found, using a harmonic oscillator model, to be consistent with a reduction in the local slope of the notch-induced confining potential at its edge.

cond-mat.mes-hall↗

arXiv2015

Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque

Spin-orbit effects [1-4] have the potential of radically changing the field of spintronics by allowing transfer of spin angular momentum to a whole new class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed that by depositing Platinum (Pt, a normal metal) on top of a 1.3 $μ$m thick Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer spin angular momentum through the interface between these two different materials. The outstanding feature was the detection of auto-oscillation of the YIG when enough dc current was passed in the Pt. This finding has created a great excitement in the community for two reasons: first, one could control electronically the damping of insulators, which can offer improved properties compared to metals, and here YIG has the lowest damping known in nature; second, the damping compensation could be achieved on very large objects, a particularly relevant point for the field of magnonics [6,7] whose aim is to use spin-waves as carriers of information. However, the degree of coherence of the observed auto-oscillations has not been addressed in ref. [5]. In this work, we emphasize the key role of quasi-degenerate spin-wave modes, which increase the threshold current. This requires to reduce both the thickness and lateral size in order to reach full damping compensation [8] , and we show clear evidence of coherent spin-orbit torque induced auto-oscillation in micron-sized YIG discs of thickness 20 nm.

cond-mat.mtrl-sci↗

arXiv2014

Graphene-Passivated Nickel as an Oxidation-Resistant Electrode for Spintronics

We report on graphene-passivated ferromagnetic electrodes (GPFE) for spin devices. GPFE are shown to act as spin-polarized oxidation-resistant electrodes. The direct coating of nickel with few layer graphene through a readily scalable chemical vapour deposition (CVD) process allows the preservation of an unoxidized nickel surface upon air exposure. Fabrication and measurement of complete reference tunneling spin valve structures demonstrates that the GPFE is maintained as a spin polarizer and also that the presence of the graphene coating leads to a specific sign reversal of the magneto-resistance. Hence, this work highlights a novel oxidation-resistant spin source which further unlocks low cost wet chemistry processes for spintronics devices.

cond-mat.mtrl-sci↗

arXiv2014

Spintronics with graphene

Because of its fascinating electronic properties, graphene is expected to produce breakthroughs in many areas of nanoelectronics. For spintronics, its key advantage is the expected long spin lifetime, combined with its large electron velocity. In this article, we review recent theoretical and experimental results showing that graphene could be the long-awaited platform for spintronics. A critical parameter for both characterization and devices is the resistance of the contact between the electrodes and the graphene, which must be large enough to prevent quenching of the induced spin polarization but small enough to allow for the detection of this polarization. Spin diffusion lengths in the 100-μm range, much longer than those in conventional metals and semiconductors, have been observed. This could be a unique advantage for several concepts of spintronic devices, particularly for the implementation of complex architectures or logic circuits in which information is coded by pure spin currents.

cond-mat.mtrl-sci↗

arXiv2014

Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt

We report on an experimental study on the spin-waves relaxation rate in two series of nanodisks of diameter $ϕ=$300, 500 and 700~nm, patterned out of two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance force microscope, we measure precisely the ferromagnetic resonance linewidth of each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth in the nanostructure is sensibly smaller than the one measured in the extended film. Analysis of the frequency dependence of the spectral linewidth indicates that the improvement is principally due to the suppression of the inhomogeneous part of the broadening due to geometrical confinement, suggesting that only the homogeneous broadening contributes to the linewidth of the nanostructure. For the bare YIG nano-disks, the broadening is associated to a damping constant $α= 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for the series with Pt cap layer, attributed to the spin pumping effect. The measured enhancement allows to extract the spin mixing conductance found to be $G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ Ω^{-1}\text{m}^{-2}$ for our YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the design of YIG based nanostructures with optimized magnetic losses.

cond-mat.mtrl-sci↗

arXiv2013

Highly efficient spin transport in epitaxial graphene on SiC

Spin information processing is a possible new paradigm for post-CMOS (complementary metal-oxide semiconductor) electronics and efficient spin propagation over long distances is fundamental to this vision. However, despite several decades of intense research, a suitable platform is still wanting. We report here on highly efficient spin transport in two-terminal polarizer/analyser devices based on high-mobility epitaxial graphene grown on silicon carbide. Taking advantage of high-impedance injecting/detecting tunnel junctions, we show spin transport efficiencies up to 75%, spin signals in the mega-ohm range and spin diffusion lengths exceeding 100 μm. This enables spintronics in complex structures: devices and network architectures relying on spin information processing, well beyond present spintronics applications, can now be foreseen.

cond-mat.mtrl-sci↗

arXiv2012

Magnetic domain wall motion by spin transfer

The discovery that a spin polarized current can exert a large torque on a ferromagnet through a transfusion of spin angular momentum, offers a new way to control a magnetization by simple current injection, without the help of an applied external field. Spin transfer can be used to induce magnetization reversals and oscillations, or to control the position of a magnetic domain wall. In this review, we focus on this last mechanism, which is today the subject of an extensive research, both because the microscopic details for its origin are still debated, but also because promising applications are at stake for non-volatile magnetic memories.

cond-mat.mtrl-sci↗