On-line SPICE-SPIN+X Seminars

On-line Seminar: 15.03.2023 - 15:00 German Time

Hidden magnetoelectric order

Nicola Spaldin, ETH Zurich

Most magnetic materials, phenomena and devices are well described in terms of magnetic dipoles of either spin or orbital origin. There is mounting evidence, however, that the existence and ordering of higher-order magnetic multipoles can lead to intriguing magnetic behaviors, which are often attributed to "hidden order" since they are difficult to characterize with conventional probes. In this talk I will discuss the relevance of the so-called magnetoelectric multipoles, which form the next-order term, after the magnetic dipole, in the multipolar expansion of the energy of a magnetization energy in a magnetic field. First I will describe how magnetoelectric multipoles underlie multiferroic behavior and in particular how they determine the magnetic response to applied electric fields. Then I will discuss signatures of hidden magnetoelectric multipolar order, how it can be unearthed using density functional calculations and possibilities for its direct measurement. Finally, I will show that the bulk magnetoelectric multipolization manifests at surfaces as a magnetization, and explore an analogy with the bulk electric polarization and its associated surface charge.
 

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 22.02.2023 - 15:00 German Time

Exploring spintronics at unconventional hybrid interfaces

Angela Wittmann, JGU

Controlled manipulation of a system allows for systematic investigation of the underlying interactions and phenomena. Simultaneously, tunability also enables the development of novel materials systems and devices customized for specific applications. Here, we will focus on materials systems that conventionally have not been used as active components in spintronic devices. We will explore the impact of strain on the antiferromagnetic domain structure via magneto-elastic coupling [1]. Furthermore, we will delve into hybrid molecule-magnetic interfaces. Molecules offer a unique way of controlling and varying the structure at the interface making it possible to precisely tune the spin injection and diffusion by molecular design [2]. In particular, chirality has gained recent interest in the context of the chiral-induced spin selectivity effect [3]. Here, we will explore signatures of spin filtering at a non-magnetic chiral molecule-metal interface paving the path toward novel hybrid spintronics.

[1] Wittmann, A. et al. Role of substrate clamping on anisotropy and domain structure in the canted antiferromagnet a-Fe2O3. Phys. Rev. B 106, 224419 (2022).
[2] Wittmann, A. et al. Tuning Spin Current Injection at Ferromagnet-Nonmagnet Interfaces by Molecular Design. Phys. Rev. Lett. 124, 027204 (2020).
[3] Naaman, R., Paltiel, Y. & Waldeck, D. H. Chiral molecules and the electron spin. Nat. Rev. Chem. 3, 250–260 (2019).

 

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 01.03.2023 - 15:00 German Time

Coherent manipulation of spins in diamond via spin-wave mixing

Toeno van der Sar, TU Delft

Coherent manipulation of spins in diamond via spin-wave mixing Magnetic imaging based on nitrogen-vacancy (NV) spins in diamond enables probing condensed matter systems with nanoscale resolution[1]. In this talk I will introduce NV magnetometry as a tool for imaging spin waves – the wave-like spin excitations of magnetic materials. Using the NV sensitivity to microwave magnetic fields, we can map coherent spin waves[2] and incoherent magnon gases[3] and provide insight into their interaction and damping[4]. By using a single NV in a scanning diamond tip we gain access to spin-wave scattering at the nanoscale[5]. I will highlight how we can use spin-wave mixing to generate frequency combs that enable high-fidelity, coherent control of the NV spins even when the applied microwave drive fields are far detuned from the NV spin resonance frequency 6 (Fig. 1). These results form a basis for developing NV magnetometry into a tool for characterizing spin-wave devices and expand the control and sensing capabilities of NV spins.

[1] Casola, F., Van Der Sar, T. & Yacoby, A. Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond. Nat. Rev. Mater. 3, 17088 (2018).
[2] Bertelli, I. et al. Magnetic resonance imaging of spin-wave transport and interference in a magnetic insulator. Sci. Adv. 6, eabd3556 (2020).
[3] Simon, B. G. et al. Directional Excitation of a High-Density Magnon Gas Using Coherently Driven Spin Waves. Nano Lett. 21, 8213–8219 (2021).
[4] Bertelli, I. et al. Imaging Spin‐Wave Damping Underneath Metals Using Electron Spins in Diamond. Adv. Quantum Technol. 4, 2100094 (2021).
[5] Simon, B. G. et al. Filtering and imaging of frequency-degenerate spin waves using nanopositioning of a single-spin sensor. Nano Lett. 22, 9198 (2022).
[6] Carmiggelt, J. J. et al. Broadband microwave detection using electron spins in a hybrid diamondmagnet sensor chip. Nat. Commun. 14, 490 (2022)

 

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 29.03.2023 - 15:00 German Time

Probabilistic spintronics – Computing and Device Physics

Shunsuke Fukami, Tohoku University

Probabilistic behavior of physical system is mostly regarded as a nuisance in conventional electronics. Contrary to this perception, here I show that properly designed probabilistic systems is even useful for unconventional computers that address complex problems more efficiently than conventional computing hardware, and spintronic systems can be a prime candidate on that front, opening a new paradigm, probabilistic spintronics.
In this seminar, I will show some proof-of-concepts of the spintronic probabilistic computers and describe how the computers can be constructed from probabilistic spintronic devices and how it solves computationally hard problems [1-4]. I will also discuss the physics governing the probabilistic behavior of spintronics devices and strategy to develop the devices for high-performance probabilistic computers [5-9].

[1] K. Camsari et al., Phys. Rev. X 7, 031014 (2017).
[2] W. A. Borders et al., Nature 573, 390 (2019).
[3] J. Kaiser et al., Phys. Rev. Appl. 17, 014016 (2022).
[4] A. Grimardi et al., IEEE IEDM 2022, 22.4 (2022).
[5] S. Kanai et al., Phys. Rev. B 103, 094423 (2021).
[6] K. Hayakawa et al., Phys. Rev. Lett. 126, 117202 (2021).
[7] K. Kobayashi et al., Appl. Phys. Lett. 119, 132406 (2021).
[8] T. Funatsu et al., Nat. Comm. 13, 4079 (2022).
[9] K. Kobayashi et al., Phys. Rev. Appl. 18, 054085 (2022).

 

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 15.02.2023 - 15:00 German Time

A stride down the quantum materials roadmap

Alberta Bonanni, Johannes Kepler University

Lately, condensed matter physics has witnessed the emergence of material systems in which quantum effects persist over a wide range of energy and length scales [1]. Such quantum materials include, among others, topological insulators, topological crystalline insulators, magnetically doped topological quantum materials, superconductors, 2-dimensional (2D). van der Waals, Kitaev and spin-orbit systems [2]. Here, the striking properties of quantum materials will be highlighted through a collection of relevant examples overarching the Rashba spin-orbit coupling in wurtzite n-GaN:Si [3,4] and the intriguing electronic properties of the magnetically doped topological crystalline insulator SnTe [5] and of the intrinsic ferromagnetic topological insulator MnSb2Te4. Striding further down the quantum materials road, the emergence of quantum chiral anomaly in 2D Weyl semimetal Td-WTe2with a record temperature of 100 K will be addressed [6]. Moreover, a bosonic island percolation model for Fe-doped superconducting NbN thin films will be presented [7]. Finally, an outlook of emergent phenomena in hybrid quantum structures with particular attention to topology, symmetry, spin-orbit coupling and superconductivity will be provided.

[1] B. Keimar et al. Nat. Phys. 13, 1045 (2017)
[2] F. Giustino et al. J. Phys. Mater. 3, 042006 (2020)
[3] W. Stefanowicz et al. Phys. Rev. B 89, 205201 (2014)
[4] R. Adhikari et al. Phys. Rev. B 94, 085205 (2016)
[5] R. Adhikari et al. Phys. Rev. B 100, 134422 (2019)
[6] R. Adhikari et al. Nanomaterials 11, 2755 (2021)
[7] R. Adhikari et al. Nanomaterials 12, 3105 (2022)

 

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 25.01.2023 - 15:00 German Time

Developments in ultrafast electron microscopy

Claus Ropers, MPI for Biophysical Chemistry and University of Göttingen

Providing the most detailed views of atomic-scale structure and composition, Transmission Electron Microscopy (TEM) serves as an indispensable tool for structural biology and materials science. The combination of electron microscopy with pulsed electrical or optical stimuli allows for the study of transient phenomena, involving magnetization dynamics, strain evolution and structural phase transformations. Ultrafast transmission electron microscopy (UTEM) is a pump-probe technique, in which non-equilibrium processes can be tracked with simultaneous femtosecond temporal and nanometer to atomic-scale spatial resolutions.
This talk will cover recent methodical developments and applications in UTEM based on laser-triggered field emitters, including real-space imaging [1] and ultrafast nanobeam diffraction [2] of a structural phase transition. Moreover, the mechanisms involved in free-electron beams interacting with optical fields at photonic structures will be discussed, emphasizing quantum effects. In particular, recent progress in the coupling of electron beams to whispering gallery modes [3] and integrated photonic resonators [4] will be presented. Finally, using event-based electron spectroscopy, electron-energy loss measured in coincidence with cathodoluminescence is used to demonstrate the preparation and characterization of electron-photon pair states [5].

[1] "Ultrafast nanoimaging of the order parameter in a structural phase transition”, T. Danz, T. Domröse, C. Ropers, Science 371, 6527 (2022)
[2] "Light-induced hexatic state in a layered quantum material", T. Domröse et al., arXiv:2207.05571(2022)
[3] "Controlling free electrons with optical whispering-gallery modes", O. Kfir et al., Nature 582, 46 (2020)
[4] "Integrated photonics enables continuous-beam electron phase modulation", J.-W. Henke et al., Nature 600, 653 (2021)
[5] A. Feist et al., “Cavity-mediated electron-photon pairs”, Science 377, 777 (2022)

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 07.12.2022 - 15:00 German Time

Light-driven phonomagnetism

Dmytro Afanasiev, Radboud University

Light in the form of ultrashort pulses made it possible to control magnetism at the ultimate time and length scales where traditional excitation with magnetic fields fails. In particular, it has opened a novel pathway to highly efficient control antiferromagnets – materials that do not possess any net magnetization and thus are notoriously known to be insensitive to magnetic fields. One of the latest breakthroughs in the optical control of magnetism is the resonant driving of elementary lattice excitations - phonons. While phonons are intuitively associated with heating, which only destroys magnetism, recent experiments have shown that when driven by the light the phonons can be used to control and even induce magnetic order.
Here I will show you how light-driven phonons can lead to a net distortion of the crystalline lattice, able to switch between various symmetry antiferromagnetic phases and even induce a net magnetization in initially not magnetized media, all on the ultrafast timescale.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 16.11.2022 - 15:00 German Time

Towards a "complete" picture of ultrafast dynamics in the 2D ferromagnet FGT

Yoav William Windsor, FH Institute of the MPS and TU Berlin

Two dimensional materials have been the focus of intense study in recent years, with extensive effort invested in transition metal dichalcogenides. A recent addition to this is the study of 2D magnetic materials. Here we focus on one such ferromagnetic material: Fe3GeTe2. We present an overview of its ultrafast response to photoexcitation using three time-resolved probes: angle resolved photoemission (ARPES), X-ray magnetic circular dichroism (XMCD), and ultrafast electron diffraction (UED). These reflect the response of different material degrees of freedom, namely the carriers, the spins and the phonons. I will then focus primarily on the study of lattice dynamics using UED.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 30.11.2022 - 15:00 German Time

Multilayer spintronic neural networks with radio-frequency connections

Alice Mizrahi, CNRS-Thales

The combination of the two key effects of spintronics, magnetization dynamics and magneto-resistive effects, allows the realization of nano-neurons and nano-synapses with high computational capabilities. However, multilayer spintronic neural networks have never been realized with these nanodevices because there is no way to connect them that can work on a large scale. I will show that it is possible to exploit the two key effects of spintronics to connect together magnetic tunnel junctions that implement both neurons and synapses of a multilayer network. The magnetic tunnel junctions perform neural operations on DC signals and output the result as RF, operate synaptic operations on RF signals and output the result as DC thus giving rise to multilayer networks based on successive, clean, and fast conversions from RF to DC and from DC to RF. I will give a proof of concept with a two-layer neural network composed of nine interconnected magnetic tunnel junctions functioning as both synapses and neurons and experimentally demonstrate its ability to solve non-linear tasks with high performance. I will show that with junctions downscaled to 20 nm, such a network would consume 10fJ per synaptic operation and 100fJ per neuronal operation, several orders of magnitude less than current software neural network implementations. Finally, I will show through physical simulations that these networks, which can process DC data, can also natively classify RF inputs, achieving state-of-the-art drone identification from their RF transmissions. This study lays the foundation for deep spintronic neural networks at the nanoscale.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 14.12.2022 - 15:00 German Time

Skyrmions in chiral magnetic multilayers

Christopher Marrows, University of Leeds

Magnetic skyrmions are topologically-nontrivial spin textures with particle-like properties [1]. Their size, topological stability, and mobility suggest their use in future generations of spintronic devices, the prototype of which is the skyrmion racetrack [2]. To realise a racetrack requires three basic operations: the nucleation (writing), propagation (manipulation), and detection (reading) of a skyrmion, all by electrical means. Here we show that all three are experimental feasible at room temperature in Pt/Co/Ir or Pt/CoB/Ir multilayers in which the different heavy metals above and below the magnetic layer break inversion symmetry and induce chirality by means of the Dzyaloshinskii-Moriya interaction, defining the structure of Néel skyrmion spin textures [3]. We show deterministic nucleation on nanosecond timescales using an electrical point contact on top of the multilayer [4] (Figure 1), current-driven propagation along a wire in which the skyrmions are channelled by defects in the multilayer [5], and their detection by means of the Hall effect (Figure 2) that reveals an unexpectedly large contribution to the Hall signal that correlates with the topological winding number [6].

[1] N. Nagaosa & Y. Tokura, Nat. Nanotech. 8, 899 (2013)
[2] A. Fert et al. Nature Nanotech. 8, 152 (2013)
[3] K. Zeissler et al. Sci. Rep. 7, 15125 (2017)
[4] S. Finizio et al., Nano Lett. 19, 7246 (2019)
[5] K. Zeissler et al., Nature Comm. 11, 428 (2020)
[6] K. Zeissler et al. Nature Nanotech. 13, 1161 (2018)

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