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On-line SPICE-SPIN+X Seminars

On-line Seminar: 12.06.2024 - 15:00 CEST

TBA

José J.Baldoví, University of Valencia


TBA

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 29.05.2024 - 15:00 CEST

Fluctuation-driven phenomena in the kagome-net magnets RMn_6Sn_6

Igor Mazin, George Mason University

I will discuss four different nontrivial manifestations of spin fluctuations in 166 materials:
1) Mn spin fluctuation in Y166 and Er166 generate (at finite temperature) topological Hall effect
2) Tb spin fluctuations in Tb166 trigger a spontaneous spin-reorientation transitions
3) Er spin fluctuations trigger a ferrimagnet-spiral transition
4) RE and Mn spin fluctuations modify the conventional scaling of the anomalous Hall effect.

This shows that spin fluctuations can have qualitatively diverse and nontrivial effects already on the mean field level, i.e. outside of the standard framework of suppressing the long-range order and triggering order from disorder transitions.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 27.03.2024 - 15:00 CET

Chiral spin textures on the racetrack

Stuart Parkin, MPI Halle

The simplest chiral spin texture is a one-dimensional Néel magnetic domain wall that separates two magnetic regions that are magnetized in opposite directions. Under the influence of spin orbit torques, that are derived from spin currents that carry angular momentum, these walls can be driven at high speeds exceeding 1 km/sec along magnetic nano-wires that, thereby, form “magnetic racetracks”. This is the basic principle of the magnetic racetrack memory that stores digital data in the form of the presence or absence of such chiral domain walls. We discuss recent developments including the scaling of racetrack to sub-100 nm widths and the first 3D racetrack memory devices. Chiral domain walls are, however, just one member of an ever-expanding family of chiral spin textures that are of great interest from both a fundamental as well as a technological perspective. Recently a zoology of complex 2D and 3D spin textures stabilized by volume or interface Dzyaloshinskii-Moriya vector exchange interactions have been discovered including, in our work, anti-skyrmions, elliptical Bloch skyrmion, two-dimensional Néel skyrmions and fractional antiskyrmions. Such nano-objects are potential candidates as magnetic storage bits on the racetrack. Another class of chiral spin textures are Kagome antiferromagnets: we have recently shown how their complex spin textures can be manipulated by a previously unobserved seeded spin orbit torque (SSOT) mechanism. These chiral spin textures become superconducting when placed in proximity to a conventional superconductor and support long range triplet supercurrents. Triplet supercurrents are highly interesting in that they can carry spin angular momentum, unlike conventional superconductors, and, therefore, could be used, in principle, to manipulate chiral spin textures at ultra-low temperatures. This is the basic principle of the SUPERTRACK memory device that I have recently proposed [1].
[1] European Research Council Advanced Grant– SUPERMINT awarded to Stuart S.P. Parkin April, 2022.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 24.04.2024 - 15:00 CEST

Exploring d-d Transition Dynamics in FePS3: A Journey through Magneto-Optical and Photoelectron Spectroscopy Investigations

Mirko Cinchetti, TU Dortmund University

Excitations between localized 3d states of transition metal ions within crystalline solids, commonly known as d-d transitions, play a pivotal role in diverse phenomena across solid-state physics, materials science, and chemistry. These transitions contribute significantly to the optical properties of transition metal oxides, catalytic activity on oxide surfaces, high-temperature superconductivity, and magnetic behaviors, facilitating spin-crossover transitions and linking optical excitation to quantized phenomena such as phonons and magnons. The discovery of unique effects in two-dimensional (2D) antiferromagnets, such as electron-phonon bound states, sub-terahertz (sub-THz) frequency magnon modes, and hybridized phonon-magnon modes, highlights the complex phenomenology driven by d-d transitions.
In this presentation, I will discuss our recent investigations into FePS3, selected for its promise as a scalable van der Waals antiferromagnetic semiconductor that retains magnetic order even at the 2D limit. We employed two complementary experimental approaches. Initially, pump-probe magneto-optical measurements were conducted to observe laser-driven lattice and spin dynamics. Pumping in resonance with a d-d transition within the Fe2+ multiplet induced a coherent phonon mode oscillating at 3.2 THz. Remarkably, this mode is excitable in a low optical absorption regime, safeguarding even single antiferromagnetic layers from damage. The mode's amplitude diminishes with increasing temperature, disappearing at the Néel temperature as the system transitions to a paramagnetic phase, thereby illustrating its connection to long-range magnetic order. Furthermore, in an external magnetic field, this 3.2 THz phonon mode hybridizes with a magnon mode, enabling optical excitation of the resultant phonon-magnon hybrid mode [1].
Additionally, we utilized angle-resolved photoelectron spectroscopy (ARPES) to probe the electronic structure in its ground state [2] and employed time-resolved ARPES to capture the ultrafast dynamics of selected spin-allowed and spin-forbidden d-d transitions in FePS3 [3]. The insights from magneto-optical experiments, juxtaposed with ARPES findings, shed light on the intricate quasiparticle dynamics underpinning d-d transitions in FePS3, offering a deeper understanding of their role in quantum material behaviors.

[1] F. Mertens, et al. Advanced Materials (2023).https://doi.org/10.1002/adma.202208355
[2] J.E. Nitschke, et al. Materials Today Electronics (2023). https://doi.org/10.1016/j.mtelec.2023.100061
[3] J.E. Nitschke, et al. arXiv (2024). arXiv:2402.03018

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 10.04.2024 - 15:00 CEST

Mapping and controlling topological textures
in 3D magnetic systems

Claire Donnelly, MPI CPfS

Three dimensional magnetic systems promise significant opportunities for applications, for example providing higher density devices and new functionalities associated with complex topology and greater degrees of freedom [1,2]. Extending to three dimensions allows for the formation of new topologies of spin textures, for example containing defects in 3D such as Bloch point singularities, or truly three-dimensional topological structures such as magnetic torons or hopfions.
In this talk, I will address two main questions: first, can we observe and understand such three-dimensional topological magnetic textures, and second, can we control them?
For the observation and understanding of these three-dimensional textures, we have developed magnetic X-ray tomographic techniques, that open the possibility to map both the three-dimensional magnetic structure [3], and its dynamical response to external excitations [4,5]. In this way, we have observed 3D magnetic solitons which we identify as nanoscale magnetic vortex rings, as well as torons that contain Bloch point singularities [6,7].
However, while X-ray magnetic tomography is now a relatively well-established technique, high resolution imaging of extended magnetic systems has so far been limited to rare-earth containing materials. To this end, I will present recent results of soft X-ray dichroic ptychography where the phase dichroism offers a route to imaging magnetic systems that until now have not been accessible [8].
As well as naturally existing within the bulk, 3D spin textures can be introduced and controlled via the patterning of 3D curvilinear geometries [9]. I will discuss how, in this way, not only can new states be realized [10], but the energy landscape of topological defects can be designed through the local patterning of curvature induced chirality [11].
This new understanding and control of topological textures in 3D magnetic systems paves the way not only for enhanced understanding of these systems, but also towards the next generation of technological devices.

[1] Fernández-Pacheco et al., Nature Communications 8, 15756 (2017).
[2] C. Donnelly and V. Scagnoli, J. Phys. D: Cond. Matt. 32, 213001 (2020).
[3] C. Donnelly et al., Nature 547, 328 (2017).
[4] C. Donnelly et al., Nature Nanotechnology 15, 356 (2020).
[5] S. Finizio et al., Nano Letters (2022)
[6] C. Donnelly et al., Nat. Phys. 17, 316 (2021)
[7] N. Cooper, PRL. 82, 1554 (1999).
[8] Neethirajan et al., arXiv:2309.14969 [cond-mat.mes-hall]

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 03.04.2024 - 15:00 CEST

Magnetic hopfion rings

Nikolai Kiselev, FZ Juelich

Magnetic solitons are localized magnetization field configurations in crystals that exhibit properties similar to ordinary particles. For example, under different external stimuli such as magnetic fields, temperature gradients, or electric currents, magnetic solitons can move and interact with one another. These characteristics make magnetic solitons promising candidates for applications in information transfer and data storage. The most well-known example of magnetic solitons is skyrmions in chiral magnets. Skyrmions in 2D materials and skyrmion strings in bulk samples represent quasi-two-dimensional configurations. The three-dimensional magnetic solitons, also known as hopfions, were theoretically predicted in several magnetic systems. Hopfions can be conceptualized as closed twisted skyrmion strings. In the simplest scenario, hopfions form toroidal or ring-like structures localized within a small volume of the magnetic sample. We present the first experimental observation of 3D topological magnetic solitons in magnetic crystals, particularly hopfions linked to skyrmion strings in B20-type FeGe, through high-resolution transmission electron microscopy. I will discuss various aspects of hopfion rings, including a highly reproducible protocol for hopfion ring nucleation, the diversity of configurations of hopfion rings linked with one or a few skyrmion strings, hopfion ring zero modes, etc.

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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.

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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.

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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.

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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.

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