Showing papers by "Michel Viret published in 2020"

Spin Insulatronics

Abstract: Spin insulatronics covers efforts to generate, detect, control, and utilize high-fidelity pure spin currents and excitations inside magnetic insulators. Ultimately, the new findings may open doors for pure spin-based information and communication technologies. The aim is to replace moving charges with dynamical entities that utilize low-dissipation coherent and incoherent spin excitations in antiferromagnetic and ferromagnetic insulators. The ambition is that the new pure spin-based system will suffer reduced energy losses and operate at high frequencies. In magnetic insulators, there are no mobile charge carriers that can dissipate energy. Integration with conventional electronics is possible via interface exchange interactions and spin-orbit couplings. In this way, the free electrons in the metals couple to the localized spins in the magnetic insulators. In turn, these links facilitate spin-transfer torques and spin-orbit torques across metal-insulator interfaces and the associated phenomena of spin-pumping and charge-pumping. The interface couplings also connect the electron motion inside the metals with the spin fluctuations inside the magnetic insulators. These features imply that the system can enable unprecedented control of correlations resulting from the electron-magnon interactions. We review recent developments to realize electric and thermal generation, manipulation, detection, and control of pure spin information in insulators.

Electric and antiferromagnetic chiral textures at multiferroic domain walls

Abstract: Chirality, a foundational concept throughout science, may arise at ferromagnetic domain walls 1 22 and in related objects such as skyrmions 2. However, chiral textures should also exist in other types 23 of ferroics such as antiferromagnets for which theory predicts that they should move faster for 24 lower power 3 , and ferroelectrics where they should be extremely small and possess unusual 25 topologies 4,5. Here we report the concomitant observation of antiferromagnetic and electric chiral 26 textures at domain walls in the room-temperature ferroelectric antiferromagnet BiFeO 3. 27 Combining reciprocal and real-space characterization techniques, we reveal the presence of 28 periodic chiral antiferromagnetic objects along the domain walls as well as a priori energetically 29 unfavorable chiral ferroelectric domain walls. We discuss the mechanisms underlying their 30 formation and their relevance for electrically controlled topological oxide electronics and 31 spintronics. 32 33 Metallic ferromagnets have been the elemental bricks of spintronics for the last three decades and 34 continue to hold promises on the basis of non-collinear chiral spin textures such as skyrmions. These 35 topologically protected objects are envisioned to be the future of magnetic data storage thanks to 36 their specific stability, dynamics, and scalability 2. In parallel, antiferromagnets (AFs) are emerging as a 37 new paradigm for spintronics 6. They are intrinsically stable (being insensitive to spurious magnetic 38 fields), scalable (no cross talk between neighbouring memory cells), and fast (switching frequencies 39 in the THz regime). The opportunity of gathering the best of these two worlds and realize 40 "antiferromagnetic skyrmions" is then tremendously appealing but faces at least two major 41 challenges. The first one is to achieve antiferromagnetic chirality and the second one is to identify 42 appropriate control stimuli to create, annihilate and move these chiral objects. 43 On one hand, chirality may naturally emerge at domain walls. The antiferromagnetic domain wall 44 structure is a virtually uncharted territory but this is where translational symmetry is broken and spin 45 rotation favoured. On the other hand, AF manipulation is hampered by the intrinsic lack of net 46 magnetization, which prevents a straightforward magnetic actuation. This fundamental issue may be 47

Antiferromagnetic textures in BiFeO 3 controlled by strain and electric field

Abstract: Antiferromagnetic thin films are currently generating considerable excitement for low dissipation magnonics and spintronics. However, while tuneable antiferromagnetic textures form the backbone of functional devices, they are virtually unknown at the submicron scale. Here we image a wide variety of antiferromagnetic spin textures in multiferroic BiFeO3 thin films that can be tuned by strain and manipulated by electric fields through room-temperature magnetoelectric coupling. Using piezoresponse force microscopy and scanning NV magnetometry in self-organized ferroelectric patterns of BiFeO3, we reveal how strain stabilizes different types of non-collinear antiferromagnetic states (bulk-like and exotic spin cycloids) as well as collinear antiferromagnetic textures. Beyond these local-scale observations, resonant elastic X-ray scattering confirms the existence of both types of spin cycloids. Finally, we show that electric-field control of the ferroelectric landscape induces transitions either between collinear and non-collinear states or between different cycloids, offering perspectives for the design of reconfigurable antiferromagnetic spin textures on demand.

Ultrafast antiferromagnetic switching in NiO induced by spin transfer torques

Abstract: NiO is a prototypical antiferromagnet with a characteristic resonance frequency in the THz range. Using the spin transfer torque mechanism, we describe antiferromagnetic switching at this frequency, thus opening the possibility to speed up current logic of electronic devices by several orders of magnitude. We use atomistic spin dynamics simulations taking into account the crystallographic structure of NiO and in particular using a magnetic anisotropy respecting its symmetry. Sub-picosecond S-domain switching between the six allowed stable spin directions is found for reasonably achievable spin currents. We thus describe a simple procedure for picosecond writing of a six state memory and comment on the consequences for a possible NiO based antiferromagnetic oscillator.

Ultrafast light-induced shear strain probed by time-resolved x-ray diffraction: Multiferroic BiFeO 3 as a case study

Abstract: Enabling the light control of complex systems on ultrashort timescales gives rise to rich physics with promising applications. Although crucial, the quantitative determination of both the longitudinal and the shear photoinduced strains still remains challenging. Here, by scrutinizing asymmetric Bragg peaks pairs $(\ifmmode\pm\else\textpm\fi{}h01)$ in ${\mathrm{BiFeO}}_{3}$ using picosecond time-resolved x-ray diffraction experiments, we simultaneously determine the longitudinal and shear strains. Importantly, we reveal a difference in the dynamical response of the longitudinal strain with respect to the shear one due to an interplay of quasilongitudinal and quasitransverse acoustic modes, well reproduced by our model. Finally, we show that the relative amplitude of those strains can be explained only if both thermal and nonthermal processes contribute to the acoustic phonon photogeneration process.

Origin of the magnetic properties of Fe-implanted 4H-SiC semiconductor

Abstract: p-doped 4H-SiC substrates were implanted with 57Fe ions at energies ranging from 30 to 160 keV and subjected to a rapid thermal annealing in order to produce a homogeneous Fe concentration inside a 100 nm-thick region in the semiconducting SiC material. Using 57Fe Conversion Electron Mossbauer Spectrometry and Superconducting Quantum Interference Device magnetometry, we give evidence that the ferromagnetism obtained in SiC implanted with a 57Fe atoms concentration close to 2% is not only due to the formation of some Fe–Si magnetic nanoparticles but also originates from magnetic Fe atoms diluted in the matrix of the semiconductor. So, values of Fe atoms magnetizations contained in nanoparticles and Fe atoms diluted in the matrix and the Curie temperatures associated with the nanoparticles and to the matrix have been determined.