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10.10.2023 – Terahertz Spintronics: toward Terahertz Spin-based Devices

Terahertz Spintronics: toward Terahertz Spin-based Devices

THz spintronics is a novel research field that combines magnetism and spintronic with ultrafast optics. Although ultrafast demagnetization of ferromagnetic materials at picosecond timescale has been first observed already three decades ago, recent years have seen the rapid development of THz spintronic devices stemming from ground breaking studies. Many studies pushed the GHz limits of standard spintronic devices to the THz range by investigating new materials and spin-orbit interactions at ultrafast time scale. Especially, the development of broadband and high power spintronic THz emitters based on simple nanometer thin ferromagnetic / heavy metal bilayers holds the prospect to extend the THz field and widen its applications that has long while been limited to niches for astronomers and spectroscopists.

In the last years, the numerous improvements made in material research (such as on topological insulators and antiferromagnetic materials), interface quality and device engineering have been central to both explore spin-based physics at THz frequencies and investigate to new concepts of spin based THz devices. These cover the full THz block chain (broad and narrowband THz generation and detection, together with control of radiation properties such as polarization and ellipticity) as well as new approaches for THz imaging and encoding THz information. The widespread interest and progress in spin-based THz physics and devices continues to accelerate requiring joint efforts from magnetism, optics and engineering research communities. This workshop will bring together world-leading scientists from these broad range of communities, generating further collaborations and developmentsin this emerging field.

For videos of the talks and further information, please visit the workshop home page.

25.07.2023 – Young Research Leaders Group Workshop: Recent advances in non-equilibrium and magnetic phenomena

Young Research Leaders Group Workshop: Recent advances in non-equilibrium and magnetic phenomena

In nature, all the most interesting phenomena are non-equilibrium processes, whether it be star explosions, hurricanes or electrons flowing in metals. In recent decades, the invention of new theoretical tools combined with considerable gains in computational power have enabled physicists to investigate and understand increasingly sophisticated non-equilibrium systems.
Magnetic systems provide an excellent playground for investigating non-equilibrium phenomena. Spins couple effectively to temperature gradients, oscillating magnetic fields, charge and heat currents, or laser pulses. This gives rise to phenomena like magnon BEC, the ultrafast switching of magnetic domains, novel types of phase transitions, or rapidly moving magnetic skyrmions and domain walls.
At the same time, the language of quantum magnetism can also be used to describe completely different kinds of systems, for example ultracold atoms in cavities or the qubits of quantum computers. These systems provide new ideas and challenges to the field of non-equilibrium magnetism, e.g., on the role of dissipation, measurement and entanglement.

By bringing together young researchers from both magnetism and more broad non-equilibrium topics with theoretical and experimental backgrounds we hope to learn about each others’ areas of expertise and build future collaborations to advance these fields. Science benefits from diversity, open communication, and different perspectives, and special care has been taken to make this event inclusive and gender-balanced.

For videos of the talks and further information, please visit the workshop home page.

27.06.2023 – Non-equilibrium Quantum Materials Design

Non-equilibrium Quantum Materials Design

Quantum materials driven out of equilibrium by strong electric fields exhibit phenomena that challenge our physical understanding of solids and could be implemented in future device technologies. Examples include photo- and current-induced transitions to metastable hidden phases, the ultrafast optical manipulation of ferroelectricity and magnetism, light-induced superconductivity, and the creation of photon-dressed topological states. While much progress has been made in characterizing these effects, turning them into real-world functionalities requires stabilizing them at high temperature, on long time scales, and with minimal input power. These challenges are inherently of a materials nature. The focus of this workshop is to bring together experts in quantum materials synthesis (single crystals, thin films, vdW heterostructures) with experimentalists and theorists investigating non-equilibrium phenomena to spark a new generation of non-equilibrium quantum materials design – that is, to create quantum materials that are specifically designed for their out-of-equilibrium response to optical and electrical perturbations. The long-term goal is to create a feedback loop between materials synthesis, experimental characterization and theory for non-equilibrium physics, similar to the successful strategies employed in equilibrium quantum materials design.

For videos of the talks and further information, please visit the workshop home page.

13.06.2023 – Quantum Spinoptics

Quantum Spinoptics

The conference aims at the interdisciplinary experiment of bringing together experts from solid state and quantum optics, in order to foster dialogue at the interface of the two communities. The goal is to plant the seed of a novel hybrid research area, where solid state systems are treated on the same footing as AMO driven-dissipative platforms, and, viceversa, where quantum optics can be reshaped by using concepts from spintronics, magnetism and the physics of correlated materials.We invite and encourage the contribution of selected speakers advancing the frontiers of any of the following fields:(i) dynamical phase transitions in driven-dissipative atomic or spin ensembles, ranging from traditional AMO platforms to spintronics and solid state devices;
(ii) quantum optics-inspired pumping schemes applied to condensed matter models;
(iii) correlated emission and dissipative engineering to build entangled states, and shape novel sub- and superradiant phenomena;
(iv) noise sensing and engineering in light-matter interfaces and NV/color centers.

For videos of the talks and further information, please visit the workshop home page.

09.05.2023 – Altermagnetism: Emerging Opportunities in a New Magnetic Phase

Altermagnetism: Emerging Opportunities in a New Magnetic Phase

This workshop focuses on the emerging magnetic material class of altermagnets. This recently discovered magnetic phase is separate from the ferromagnetic and antiferromagnetic phases that we are used to. The new altermagnetic class shows compensated magnetic ordering and alternating spin-polarization in both the direct and momentum space, with a d-wave (or higher even-parity wave) symmetry. Altermagnets span a large range of materials from insulators to superconductors, and exhibit properties characteristic of ferromagnetism, antiferromagnetism, and other unique properties that neither of the two previously known classes have.

The novel properties of altermagnets have links to many fields of research, such as spintronics, ultra-fast photo-magnetism, neuromorphics, multiferroics, magnonics, topological matter, or superconductivity. The workshop brings together junior and senior scientists from diverse research fields to explore this fascinating newly discovered magnetic phase.

For videos of the talks and further information, please visit the workshop home page.

On-line SPICE-SPIN+X Seminars

On-line Seminar: 28.02.2024 - 15:00 CET

Towards magnonic memory: reversal of nanomagnets on yttrium iron garnet by propagating spin waves

Dirk Grundler, EPFL

D. GRUNDLER1,2

1Institute of Materials (IMX), Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
2Institute of Electrical and Micro Engineering (IEM), EPFL, 1015 Lausanne, Switzerland

Magnonics based computing has regained increasing interest when micromagnetic simulations showed that ferromagnetic nanoelements control the interference of spin waves (magnons) in low-damping yttrium iron garnet (YIG) and give rise to a neural network [1]. Magnonics-based in-memory computation would be even more promising if nonvolatile magnetic bits could store directly magnon signals. I will report on our experiments which show that magnons with wavelengths down to 99 nm in YIG induce the reversal of bistable nanomagnets assisted by a small bias field [2]. We combine broadband spin-wave spectroscopy, micro-focus Brillouin light scattering and magnetic force microscopy and study the magnon-induced reversal depending on the YIG thickness, interface properties, nanomagnet shape, the magnon amplitude and their propagation length over 100 m. The magnon-induced reversal is found to be a robust effect [2] and contributes to the progress of on-chip devices which combine the concept of a neural network with an embedded magnonic memory. The work was supported by SNSF via grant 197360.

References:
[1] Papp A., Porod W., Csaba G. (2021). Nat. Commun. 12, 6422.
[2] Baumgaertl K., Grundler D. (2023). Nat. Commun. 14, 1490; Joglekar S. et al. (2023). https://arxiv.org/abs/2312.09177; Mucchietto A. et al. (2023). https://arxiv.org/abs/2312.15107 .

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 07.02.2024 - 15:00 CET

Magnon-exciton coupling in a magnetic semiconductor

Youn Jue Bae, Cornell

While magnons and excitons are energetically mismatched by orders of magnitude, their coupling can lead to efficient optical access to spin information. The ability to overcome energy mismatch between magnon and exciton combined with optical excitation and detection renders 2D magnetic semiconductors attractive candidates in quantum transducers. In this presentation, I will discuss strong magneto-electronic and magnetoelastic coupling and the implications of these couplings in the 2D van der Waals antiferromagnetic semiconductor, CrSBr. Because of both magnetic and semiconducting properties in CrSBr, excitons are highly sensitive to spin environments. Optical excitation of coherent spin waves can dynamically modulate the dielectric environment and we can probe excitons to obtain spin information. I will also discuss strong magnetoelastic coupling in CrSBr that induces transient strain fields to selectively launch a narrow range of wavevector and frequency of both coherent magnons and acoustic phonons.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 14.02.2024 - 15:00 CET

Energy, geometry, and topology of collective magnetic dynamics

Yaroslav Tserkovnyak, UCLA

I will review our recent work on transport phenomena engendered by large-angle magnetic dynamics, combining insights from differential geometry, topology, and overarching thermodynamic considerations. As a specific illustrative case, we study the transport of vorticity on curved dynamical two-dimensional magnetic membranes. We find that topological transport can be controlled by geometrically reducing symmetries, which enables processes that are not present in flat magnetic systems. To this end, we construct a vorticity 3-current obeying a continuity equation, which is immune to arbitrary local disturbances of the magnetic texture as well as spatiotemporal fluctuations of the membrane. We show how electric current can manipulate vortex transport in geometrically nontrivial magnetic systems. As an example, we propose a minimal setup that realizes an experimentally feasible energy storage device and discuss its thermodynamic efficiency in terms of a vorticity-transport counterpart of the thermoelectric "ZT" figure of merit.

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PDF file of the talk available here

On-line SPICE-SPIN+X Seminars

On-line Seminar: 13.03.2024 - 15:00 CET

Spin-Orbit torque driven antiferromagnetic oscillator

Joerg Wunderlich, University of Regensburg

P. K. Rout1, J. Godinho1, F. Vilsmeier2, R. Salikhov3, Z. Soban4, R. M. Otxoa5, C. Back2, O. Hellwig3,6, J. Wunderlich1,4

Antiferromagnetic materials have unique properties due to their alternating exchange-coupled magnetic moment arrangements, leading to exchange-field enhanced fast and complex spin dynamics. Most intriguingly, excitation in antiferromagnets with locally broken inversion symmetry can be realized by current-induced spin-orbit torque (SOT), and complex self-oscillation modes near the critical spin-flop transition have been predicted when excited by antidamping SOT.
In this work, we realize an antiferromagnetic oscillator within a nanoconstriction patterned from a synthetic antiferromagnetic (SAF) multilayer. By exploiting the magnetic rectification effect (MRE), we first identify spin-orbit torque-driven excitations of optical and acoustic antiferromagnetic modes. Then, by adding a DC current to our radiofrequency excitation, we identify damping and anti-damping like SOT contributions by both MRE and Brillouin light scattering (BLS). Using spatially and temporally resolved magneto-optical Kerr effect (tr-MOKE) measurements, we observe pi-phase shifted current-induced oscillations of the Néel order in individual reversed antiferromagnetic domains at zero applied magnetic field. Finally we find first indications of self-oscillations near the critical spin-flop transition by MRE measurements, which appear only for DC currents above a critical current density.

1 University of Regensburg (Germany)
2 Technical University of Munich (Germany)
3 Helmholtz-Zentrum Dresden-Rossendorf (Germany)
4 Institute of Physics, Czech Academy of Sciences, Prague, (Czech Republic)
5 Hitachi Cambridge Labyoratory, Cambridge (United Kingdom)
6 Chemnitz University of Technology (Germany)

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 31.01.2024 - 15:00 CET

Terahertz spinorbitronics - driving and probing spin and orbital currents at highest frequencies

Tom Seifert, FU Berlin

Launching terahertz (THz) angular-momentum currents from a magnet into a nearby material can be accomplished by laser-induced ultrafast magnetization quenching. Two channels for those ultrafast currents can be distinguished: spin and orbital angular momentum, i.e, S and L, respectively. In my talk, I will focus on the generation, propagation and detection of such laser-induced THz S and L currents in prototypical thin-film heterostructures. In detail, I will show how THz emission spectroscopy led to the development of efficient spintronic terahertz emitters relying on the spin degree of freedom [1,2]. Recently, an inversion of this emitter principle allowed for a broadband spintronic terahertz detection [3]. Finally, I will show how this experimental technique helped revealing THz L currents with a giant decay length in tungsten [4], and enabled us to measure THz spin conductances of antiferromagnetic insulators.

[1] Seifert, Tom, et al. "Efficient metallic spintronic emitters of ultrabroadband terahertz radiation." Nature photonics 10 (2016).
[2] Seifert, Tom S., et al. "Spintronic sources of ultrashort terahertz electromagnetic pulses." Applied Physics Letters 120 (2022).
[3] Chekhov, A. L., et al. "Broadband spintronic detection of the absolute field strength of terahertz electromagnetic pulses." Physical Review Applied 20 (2023).
[4] Seifert, Tom S., et al. "Time-domain observation of ballistic orbital-angular-momentum currents with giant relaxation length in tungsten." Nature Nanotechnology 18 (2023).

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PDF file of the talk available here