arXiv subjects

Yves Henry

Publications and source records attributed to Yves Henry.

15 recordsLinked to original sources

arXiv2026

Micron-sized magnonic 3-port rectilinear circulator

The development of miniaturized non-reciprocal microwave technologies compatible with integrated circuit architectures remains a critical challenge for modern information technology. Here, we present the first experimental characterization of a micron-sized prototypical magnon circulator. Taking advantage of the chiral excitation of spin-waves via nanowire gratings, we propose an original design of a circulator involving three channels of rectilinear and unidirectional spin-wave beams. We demonstrate via a full 3-port spin-wave spectroscopy a genuine spin-wave circulation between the three ports. The narrow frequency band of operation can be tuned over a broad range of frequencies ($2$-$8$ GHz) with both an external field of up to $100$ mT, and the dimensions of the grating specifying the wavevectors. This proposed scheme opens up possibilities for new architectures of integrated and miniaturized non-reciprocal microwave devices.

cond-mat.mes-hall↗

arXiv2026

Spin-polarization of the electric current in half-metallic Co$_2$MnSi Heusler thin films

Using propagating spin wave spectroscopy we measure the spin wave Doppler shift in patterned MgO/Co$_2$MnSi/MgO thin films and determine the degree of spin-polarization of the electric current. Our measurements reveal that the current is fully spin-polarized in the devices. This shows that the half-metallic character of the electron band structure translates into a fully spin polarized current flowing across the patterned films. Additionally, we measure a current-induced change of the spin-wave attenuation from which we estimate the non-adiabatic spin-transfer-torque parameter.

cond-mat.mtrl-sci↗

arXiv2025

Spin wave resonance in yttrium iron garnet stripe domains

We study a thin film yttrium iron garnet sample that exhibits magnetic stripe domains due to a small perpendicular magnetic anisotropy. Using wide-field magneto-optic Kerr effect measurements we reveal the domain pattern evolution as a function of applied field and discuss the role of the cubic anisotropy in the domain formation. Rich magnon spectra are observed in the stripe domain states, with a range of excitation conditions providing distinct spectra. The measurements are interpreted using micromagnetic simulations to provide the spatial profiles of each resonance mode. We further simulate domain patterns and resonance spectra accounting for the cubic anisotropy,with good correlation to experiment. This study highlights how non-collinear magnetic domain structures can host complex resonant behaviour in a low-damping magnetic material, with potential use in future magnonic applications.

cond-mat.mtrl-sci↗

arXiv2024

Unraveling the temperature-dependent spin-polarized electron transport in iron via spin-wave Doppler shift

An electric current flowing in a ferromagnetic metal carries spin angular momentum, i.e. it is spin-polarized. Here, we measure the spin-wave Doppler shift induced by the transfer of angular momentum from the diffusive spin-polarized electric current onto coherent spin waves in epitaxial MgO/Fe/MgO thin films. We follow this Doppler shift as function of the temperature and determine that the degree of spin-polarization of the current increases from 77$\%$ to 86$\%$ when cooling the device from 303K down to 10K. Interpreting these measurements within the two-current model, we separate the contributions from electron-surface, electron-phonon and electron-magnon scatterings to the spin-dependent resistivity of Fe.

cond-mat.mtrl-sci↗

arXiv2024

Shaping non-reciprocal caustic spin-wave beams

A caustic is a mathematical concept describing the beam formation when the beam envelope is reflected or refracted by a manifold. While caustics are common in a wide range of physical systems, caustics typically exhibit a reciprocal wave propagation and are challenging to control. Here, we utilize the highly anisotropic dispersion and inherent non-reciprocity of a magnonic system to shape non-reciprocal emission of caustic-like spin wave beams in an extended 200 nm thick yttrium iron garnet (YIG) film from a nano-constricted rf waveguide. We introduce a near-field diffraction model to study spin-wave beamforming in homogeneous in-plane magnetized thin films, and reveal the propagation of non-reciprocal spin-wave beams directly emitted from the nanoconstriction by spatially resolved micro-focused Brillouin light spectroscopy (BLS). The experimental results agree well with both micromagnetic simulation, and the near-field diffraction model. The proposed method can be readily implemented to study spin-wave interference at the sub-micron scale, which is central to the development of wave-based computing applications and magnonic devices.

cond-mat.mes-hall↗

arXiv2023

Probing Spin Wave Diffraction Patterns of Curved Antennas

We report on the dependence of curvilinear shaped coplanar waveguides on the near-field diffraction patterns of spin waves propagating in perpendicularly magnetized thin films. Implementing the propagating spin waves spectroscopy techniques on either concentrically or eccentrically shaped antennas, we show how the link budget is directly affected by the spin wave interference, in good agreement with near-field diffraction simulations. This work demonstrates the feasibility to inductively probe a magnon interference pattern with a resolution down to 1$\mu$m$^2$, and provides a methodology for shaping spin wave beams from an antenna design. This methodology is successfully implemented in the case study of a spin wave Young's interference experiment.

cond-mat.mes-hall↗

arXiv2022

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

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

cond-mat.mtrl-sci↗

arXiv2022

Finite-element dynamic-matrix approach for propagating spin waves: Extension to mono- and multilayers of arbitrary spacing and thickness

In our recent work [AIP Adv. 11, 095006], we presented an efficient numerical method to compute dispersions and spatial mode profiles of spin waves propagating in waveguides with translationally invariant equilibrium magnetization. Using a finite-element method (FEM) allowed to model two-dimensional waveguide cross sections of arbitrary shape but only finite size. Here, we extend our FEM propagating-wave dynamic-matrix approach from finite waveguides to the important practical cases of infinitely-extended mono- and multilayers of arbitrary spacing and thickness. To obtain the mode profiles and frequencies, the linearized equation of motion of magnetization is solved as an eigenvalue problem only on a one-dimensional line-trace mesh, defined along the normal direction of the layers. Being an important contribution in multilayer systems, we introduce interlayer-exchange interaction into our FEM approach. With the calculation of dynamic dipolar fields being the main focus of this paper, we also extend the previously presented plane-wave Fredkin-Koehler method to calculate the dipolar potential of spin waves in infinite layers. The major benefit of this method is that it avoids the discretization of any non-magnetic material, such as non-magnetic spacers in multilayers. Therefore, the computational effort becomes completely independent on the spacer thicknesses. Furthermore, it keeps the resulting discretized eigenvalue problem sparse, which therefore, inherits a comparably low arithmetic complexity. As a validation of our method (implemented into the open-source finite-element micromagnetic package TetraX), we present results for various systems and compare them with theoretical predictions as well as with established finite-difference numerical methods. We believe this method offers an efficient and versatile tool to calculate spin-wave dispersions in layered magnetic systems.

cond-mat.mes-hall↗

arXiv2021

Higgs and Goldstone spin-wave modes in striped magnetic texture

Spontaneous symmetry breaking is ubiquitous in physics. Its spectroscopic signature consists in the softening of a specific mode upon approaching the transition from the high symmetry side and its subsequent splitting into a zero-frequency "Goldstone" mode and a non-zero-frequency "Higgs" mode. Although they determine the whole system dynamics, these features are difficult to address in practice because of their vanishing coupling to most experimental probes and/or their strong interaction with other fluctuations. In this work, we consider a periodic magnetic modulation occurring in a ferromagnetic film with perpendicular-to-plane magnetic anisotropy and directly observe its Goldstone and Higgs spin-wave modes at room temperature using microwave and optical techniques. This simple system constitutes a particularly convenient platform for further exploring the dynamics of symmetry breaking.

cond-mat.mes-hall↗

arXiv2019

Slow-wave based magnonic diode

Spin waves, the collective excitations of the magnetic order parameter, and magnons, the associated quasiparticles, are envisioned as possible data carriers in future wave-based computing architectures. On the road towards spin-wave computing, the development of a diode-like device capable of transmitting spin waves in only one direction, thus allowing controlled signal routing, is an essential step. Here, we report on the design and experimental realization of a microstructured magnonic diode in a ferromagnetic bilayer system. Effective unidirectional propagation of spin waves is achieved by taking advantage of nonreciprocities produced by dynamic dipolar interactions in transversally magnetized media, which lack symmetry about their horizontal midplane. More specifically, dipolar-induced nonreciprocities are used to engineer the spin-wave dispersion relation of the bilayer system so that the group velocity is reduced to very low values for one direction of propagation, and not for the other, thus producing unidirectional slow spin waves. Brillouin light scattering and propagating spin-wave spectroscopy are used to demonstrate the diode-like behavior of the device, the composition of which was previously optimized through micromagnetic simulations. simulations.

physics.app-ph↗

arXiv2018

Unidirectional spin-wave channeling along magnetic domain walls of Bloch type

From the pioneering work of Winter [Phys. Rev. 124, 452 (1961)], a magnetic domain wall of Bloch type is known to host a special wall-bound spin-wave mode, which corresponds to spin-waves being channeled along the magnetic texture. Using micromagnetic simulations, we investigate spin-waves travelling inside Bloch walls formed in thin magnetic media with perpendicular-to-plane magnetic anisotropy and we show that their propagation is actually strongly nonreciprocal, as a result of dynamic dipolar interactions. We investigate spin-wave non-reciprocity effects in single Bloch walls, which allows us to clearly pinpoint their origin, as well as in arrays of parallel walls in stripe domain configurations. For such arrays, a complex domain-wall-bound spin-wave band structure develops, some aspects of which can be understood qualitatively from the single-wall picture by considering that a wall array consists of a sequence of up/down and down/up walls with opposite non-reciprocities. Circumstances are identified in which the non-reciprocity is so extreme that spin-wave propagation inside individual walls becomes unidirectional.

cond-mat.mes-hall↗

arXiv2017

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

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

cond-mat.mtrl-sci↗

arXiv2017

Conductance oscillations in graphene/nanoclusters hybrid material: towards large area single electron devices

Large assemblies of self-organized aluminum nanoclusters embedded in an oxide layer are formed on graphene templates and used to build tunnel-junction devices. Unexpectedly, single-electron-transport behavior with well-defined Coulomb oscillations is observed for a record junction area containing millions of metal islands. Such hybrid materials offer new prospects for single-electron electronics.

cond-mat.mes-hall↗

arXiv2016

Propagating spin-wave normal modes: A dynamic matrix approach using plane-wave demagnetizating tensors

We present a finite-difference micromagnetic approach for determining the normal modes of spin-waves propagating in extended magnetic films and strips, which is based on the linearized Landau-Lifshitz equation and uses the dynamic matrix method. The model takes into account both short range exchange interactions and long range dipole-dipole interactions. The latter are accounted for through plane-wave dynamic demagnetization factors, which depend not only on the geometry and relative positions of the magnetic cells, as usual demagnetization factors do, but also on the wave vector of the propagating waves. Such a numerical model is most relevant when the spin-wave medium is spatially inhomogeneous perpendicular to the direction of propagation, either in its magnetic properties or in its equilibrium magnetic configuration. We illustrate this point by studying surface spin-waves in magnetic bilayer films and spin-waves channelized along magnetic domain walls in perpendicularly magnetized strips. In both cases, dynamic dipolar interactions produce non-reciprocity effects, where counter-propagative spin-waves have different frequencies.

cond-mat.mes-hall↗

arXiv2011

Random barrier double-well model for resistive switching in tunnel barriers

The resistive switching phenomenon in MgO-based tunnel junctions is attributed to the effect of charged defects inside the barrier. The presence of electron traps in the MgO barrier, that can be filled and emptied, locally modifies the conductance of the barrier and leads to the resistive switching effects. A double-well model for trapped electrons in MgO is introduced to theoretically describe this phenomenon. Including the statistical distribution of potential barrier heights for these traps leads to a power-law dependence of the resistance as a function of time, under a constant bias voltage. This model also predicts a power-law relation of the hysteresis as a function of the voltage sweep frequency. Experimental transport results strongly support this model and in particular confirm the expected power laws dependencies of resistance. They moreover indicate that the exponent of these power laws varies with temperature as theoretically predicted.

cond-mat.mtrl-sci↗