arXiv subjects

Hugo Merbouche

Publications and source records attributed to Hugo Merbouche.

12 recordsLinked to original sources

arXiv2026

Hyperchaos in a Magnetic Nanodisk Driven by Ferromagnetic Resonance

We investigate the chaotic dynamics driven in the nonlinear regime of ferromagnetic resonance of an out-of-plane magnetized nanodisk in detail. By combining extensive micromagnetic simulations with time-series analysis across the control parameter space, we map the topological transitions from stable periodic orbits to strange attractors and quantify the dynamical complexity. Despite the simplicity of our nanoscale system, we evidence that it can exhibit hyperchaotic dynamics with up to three positive Lyapunov exponents in vast regions of the control plane accessible to experimental studies. Using a mode projection technique, we unveil that the generated complexity is related to the number of quantized spin-wave modes participating in the dynamics. Our findings establish magnon-spintronic nanodevices as versatile entropy sources for unconventional processing of information.

cond-mat.mes-hall↗

arXiv2026

Nonlinear interaction theory for parametrically-excited spin-wave modes in confined micromagnetic systems

We present a general theoretical approach for the quantitative description of parametric excitation of spin-wave modes in confined micromagnetic systems. This type of problem belongs to a broader class of nonlinear modal dynamics that arise across many areas of physics and engineering. The ferromagnetic sample is driven by parallel pumping with an external applied magnetic field having two tones at different frequencies, which are able to trigger parametric instability of two resonant modes. The two excited spin-wave modes interact in a strongly nonlinear fashion giving rise to quasiperiodicity, hysteresis and non-commutativity of steady-state oscillation regimes. To disentangle such a complex variety of dynamics, we develop a reduced-order model based on magnetization normal modes that is amenable of appropriate analytical treatment, leading to quantitative description of parametric instability thresholds, post-instability steady-state amplitude saturation and complete determination of phase diagrams for steady-state oscillation regimes. We have performed validation of the theory using numerical simulations. The phase diagrams allow to predict and explain all the features of the nonlinear interaction between the parametrically-excited spin-wave modes and can be directly compared with experimental results.

cond-mat.mes-hall↗

arXiv2026

Nonlinear mode interactions under parametric excitation in a YIG microdisk

A pair of quantized spin-wave modes is driven by two-tone parallel pumping in a YIG microdisk. The nonlinear dynamics is experimentally investigated by probing the resulting steady state, which is found to critically depend on the chosen pair of modes, the detuning between the pump frequencies and the modes parametric resonance, as well as the temporal sequence of the two rf tones. A general theory of parametric excitation in confined structures based on magnetization normal modes is developed and quantitatively accounts for the observed dependence and non-commutative behaviors, which emerge from the interplay between the self and mutual nonlinear frequency shifts of the spin-wave modes. Owing to its high degree of external controllability and scalability to larger sets of modes, this dynamical system provides a model platform for exploring nonlinear phenomena and a promising route toward rf driven state mapping relevant to neuromorphic and unconventional computing.

cond-mat.mes-hall↗

arXiv2025

Self-modulation instability in high power ferromagnetic resonance of BiYIG nanodisks

We study the high power ferromagnetic resonance (FMR) of perpendicularly magnetized BiYIG nanodisks where the uniaxial anisotropy almost compensates the shape anisotropy. We observe a strong saturation of the averaged magnetization upon moderately increasing the amplitude of the rf field and a broadening of the FMR line towards lower and higher magnetic field. Full micromagnetic simulations reveal that a self-modulation of the dynamic magnetization is responsible of this behavior. To get more insight into this unstable dynamics, it is analysed in terms of normal modes. The number of modes involved is found to rapidly increase above the critical threshold. Still, a normal modes model taking into account only a few of them and their mutual nonlinear couplings allows us to qualitatively reproduce the observed phenomenon. The normal modes analysis and micromagnetic simulations also predict a Suhl-like instability at larger excitation power when it is slowly increased from low values, and bistability. Using two-tone spectroscopy, we directly measure the self-modulation spectrum and provide experimental evidence of bistable dynamics. These findings open some perspectives of using high dimensional dynamics in magnetic nanostructures for unconventional information processing.

cond-mat.mes-hall↗

arXiv2024

Stimulated magnon scattering by non-degenerate parametric excitation

Parametric spin wave excitation allows studying a variety of nonlinear phenomena, such as magnon scattering. In patterned micro- and nanostructures the magnon spectra is discrete and translational symmetry is broken, which means allowable scattering channels differ from those in continuous films. An example is non-degenerate scattering by which high-power transverse field pumping creates two magnons with distinct frequencies around half the pumping frequency. Through micromagnetics simulations, we show under certain conditions that combining two pumping frequencies generates new magnon modes through a process of stimulated magnon scattering. Such processes are found to depend on the film geometry and sequence of the pumping fields.

cond-mat.mes-hall↗

arXiv2023

Degenerate and non-degenerate parametric excitation in YIG nanostructures

We study experimentally the processes of parametric excitation in microscopic magnetically saturated disks of nanometer-thick Yttrium Iron Garnet. We show that, depending on the relative orientation between the parametric pumping field and the static magnetization, excitation of either degenerate or non-degenerate magnon pairs is possible. In the latter case, which is particularly important for applications associated with the realization of computation in the reciprocal space, a single-frequency pumping can generate pairs of magnons whose frequencies correspond to different eigenmodes of the disk. We show that, depending on the size of the disk and the modes involved, the frequency difference in a pair can vary in the range 0.1-0.8 GHz. We demonstrate that in this system, one can easily realize a practically important situation where several magnon pairs share the same mode. We also observe the simultaneous generation of up to six different modes using a fixed-frequency monochromatic pumping. Our experimental findings are supported by numerical calculations that allow us to unambiguously identify the excited modes. Our results open new possibilities for the implementation of reciprocal-space computing making use of low damping magnetic insulators.

cond-mat.mes-hall↗

arXiv2023

True amplification of spin waves in magnonic nano-waveguides

Magnonic nano-devices exploit magnons -- quanta of spin waves -- to transmit and process information within a single integrated platform that has the potential to outperform traditional semiconductor-based electronics for low power applications. The main missing cornerstone of this information nanotechnology is an efficient scheme for the direct amplification of propagating spin waves. The recent discovery of spin-orbit torque provided an elegant mechanism for propagation losses compensation. While partial compensation of the spin-wave damping has allowed for spin-wave signal modulation, true amplification - the exponential increase in the spin-wave intensity during propagation - has so far remained elusive. Here we evidence the operating conditions to achieve unambiguous amplification using clocked nanoseconds-long spin-orbit torque pulses in sub-micrometer wide magnonic waveguides, where the effective magnetization has been engineered to be close to zero to suppress the detrimental magnon-magnon scattering. As a result, we achieve an exponential increase in the intensity of propagating spin waves up to 500 % at a propagation distance of several micrometers. These results pave the way towards the implementation of energy efficient, cascadable magnonic architectures for wave-based information processing and complex on-chip computation.

cond-mat.mes-hall↗

arXiv2023

Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning

Thin garnet films are becoming central for magnon-spintronics and spin-orbitronics devices as they show versatile magnetic properties together with low magnetic losses. These fields would benefit from materials in which heat does not affect the magnetization dynamics, an effect known as the non-linear thermal frequency shift. In this study, low damping Bi substituted Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser Deposition. Through a fine tuning of the growth parameters, the precise control of the perpendicular magnetic anisotropy allows to achieve a full compensation of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as the only tuning parameter induces the easy-axis to go from out-of-plane to in-plane. For films that are close to the dipolar compensation, Ferromagnetic Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$ that has almost no temperature dependence over a large temperature range (260 K to 400 K) resulting in an anisotropy temperature exponent of 2. These findings put Bi:YIG system among the very few materials in which the temperature dependence of the magnetic anisotropy varies at the same rate than the saturation magnetization. This interesting behavior is ascribed phenomenologically to the sizable orbital moment of $Bi^{3+}$.

cond-mat.mtrl-sci↗

arXiv2023

Complete identification of spin-wave eigenmodes excited by parametric pumping in YIG microdisks

We present the parametric excitation of spin-wave modes in YIG micro-disks via parallel pumping. Their spectroscopy is performed using magnetic resonance force microscopy (MRFM), while their spatial profiles are determined by micro-focus Brillouin light scattering (BLS). We observe that almost all the fundamental eigenmodes of an in-plane magnetized YIG micro-disk, calculated using a micromagnetic eigenmode solver, can be excited using the parallel pumping scheme, as opposed to the transverse one. The comparison between the MRFM and BLS data on one side, and the simulations on the other side, provides the complete spectroscopic labeling of over 40 parametrically excited modes. Our findings could be promising for spin-wave-based computation schemes, in which the amplitudes of a large number of spin-wave modes have to be controlled.

physics.app-ph↗

arXiv2022

Non-local magnon transconductance in extended magnetic insulating films.\\ Part I: spin diode effect

This review provides a comprehensive study of the nonlinear transport properties of magnons, which are electrically emitted or absorbed inside extended YIG films by spin transfer effects via a YIG$\vert$Pt interface. Our purpose is to experimentally elucidate the pertinent picture behind the asymmetric electrical variation of the magnon transconductance analogous to an electric diode. The feature is rooted in the variation of the density of low-lying spin excitations via an electrical shift of the magnon chemical potential. As the intensity of the spin transfer increases in the forward direction (regime of magnon emission), the transport properties of low-energy magnon go through 3 distinct regimes: \textit{i)} at low currents, where the spin current is a linear function of the electrical current, the spin transport is ballistic and set by the film thickness; \textit{ii)} for amplitudes of the order of the damping compensation threshold, it switches to a highly correlated regime limited by magnon-magnon relaxation process and marked by a saturation of the magnon transconductance. Here the main bias, that controls the magnon density, are thermal fluctuations beneath the emitter. \textit{iii)} As the temperature under the emitter approaches the Curie temperature, scattering with high-energy magnons dominates, leading to diffusive transport. We note that such sequence of transport regimes bears analogy with electron hydrodynamic transport in ultra-pure media predicted by Radii Gurzhi. This study restricted to low energy part of the magnon manifold complements part II of this review\cite{kohno_2F}, which concentrates instead on the whole spectrum of propagating magnons.

cond-mat.mes-hall↗

arXiv2022

Non-local magnon transconductance in extended magnetic insulating films.\\Part II: two-fluid behavior

This review presents a comprehensive study of the spatial dispersion of propagating magnons electrically emitted in extended yttrium-iron garnet (YIG) films by the spin transfer effects across a YIG$\vert$Pt interface. Our goal is to provide a generic framework to describe the magnon transconductance inside magnetic films. We experimentally elucidate the relevant spectral contributions by studying the lateral decay of the magnon signal. While most of the injected magnons do not reach the collector, the propagating magnons can be split into two-fluids: \textit{i)} a large fraction of high-energy magnons carrying energy of about $k_B T_0$, where $T_0$ is the lattice temperature, with a characteristic decay length in the sub-micrometer range, and \textit{ii)} a small fraction of low-energy magnons, which are particles carrying energy of about $\hbar \omega_K$, where $\omega_K/(2 \pi)$ is the Kittel frequency, with a characteristic decay length in the micrometer range. Taking advantage of their different physical properties, the low-energy magnons can become the dominant fluid \textit{i)} at large spin transfer rates for the bias causing the emission of magnons, \textit{ii)} at large distance from the emitter, \textit{iii)} at small film thickness, or \textit{iv)} for reduced band mismatch between the YIG below the emitter and the bulk due to variation of the magnon concentration. This broader picture complements part I \cite{kohno_SD}, which focuses solely on the nonlinear transport properties of low-energy magnons.

cond-mat.mes-hall↗

arXiv2021

Voltage-Controlled Reconfigurable Magnonic Crystal at the Submicron Scale

Multiferroics offer an elegant means to implement voltage-control and on the fly reconfigurability in microscopic, nanoscaled systems based on ferromagnetic materials. These properties are particularly interesting for the field of magnonics, where spin waves are used to perform advanced logical or analogue functions. Recently, the emergence of nano-magnonics {\color{black} is expected to} eventually lead to the large-scale integration of magnonic devices. However, a compact voltage-controlled, on demand reconfigurable magnonic system has yet to be shown. Here, we introduce the combination of multiferroics with ferromagnets in a fully epitaxial heterostructure to achieve such voltage-controlled and reconfigurable magnonic systems. Imprinting a remnant electrical polarization in thin multiferroic $\mathrm{BiFeO_3}$ with a periodicity of $500\,\mathrm{nm}$ yields a modulation of the effective magnetic field in the micron-scale, ferromagnetic $\mathrm{La_{2/3}Sr_{1/3}MnO_3}$ magnonic waveguide. We evidence the magneto-electrical coupling by characterizing the spin wave propagation spectrum in this artificial, voltage induced, magnonic crystal and demonstrate the occurrence of a robust magnonic bandgap with $>20 \,\mathrm{dB}$ rejection.

cond-mat.mes-hall↗