On-line SPICE-SPIN+X Seminars

On-line Seminar: 19.02.2025 - 15:00 CET

New materials and interface effects in charge and spin transport in magnetic heterostructures

Günter Reiss, University of Bielefeld

Magnetic heterostructures are key devices for spinelectronics. Their preparation requires a combination of thin film deposition with sub-Å control, field-annealing and nanopatterning. If fully functional, they can help fundamental research on new materials and effects as well open applications in sensors, memories, logic and oscillators. An introduction will present examples for basic effects and their applications.
We then will discuss several novel materials and interface induced effects occurring in magnetic heterostructures:
- The growth of altermagnetic thin films and their integration in magnetic tunnel junctions using the example of RuO2. Such altermagnets are at present intensively investigated due to their potentially spin split band structure and related spin currents. The X-ray analysis reveals a high crystalline quality of the films with or without twinning depending on the choice of the substrate. When integrated with an MgO tunnel barrier and a ferromagnetic counter electrode, signatures of a tunneling magnetoresistance can be found that strongly depend on the bias voltage and are not yet fully understood. When integrated with ferromagnets (Ni80Fe20) or heavy metals (Pt), an analysis based on the 2ω method shows the presence of torques in accordance with a spin current at the interface.
- When replacing the alter- by a ferromagnet, the heavy metal can show a proximity induced ferro-magnetism at the interface that substantially influences the results of well-known phenomena such as the spin Seebeck, anomalous Nernst or anomalous Hall effect. Examples will be discussed using metallic as well as insulating ferro- or ferrimagnets and recipes for disentangling the zoo of effects will be given.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 12.03.2025 - 15:00 CET

Static and Dynamic Properties of Insulating Antiferromagnetic Cr2O3

Jing Shi, University of California

This talk explores two distinct aspects of insulating antiferromagnetic Cr2O3. First, we demonstrate the electrical detection of the Néel vector in single-domain Cr2O3. While previous Hall effect measurements have shown promise, signal cancellation due to multi domains can reduce the signal and therefore limit unambiguous Néel vector determination. By fabricating small Pt detectors, we isolate individual magnetic domains and observe a complete reversal of the anomalous Hall signal upon switching the Néel vector. Second, I will present our study of the spin Seebeck effect in bulk Cr2O3 coupled to a homoepitaxial Cr2O3 film. We observe a significant suppression of bulk magnon transport as the film thickness increases to 9 nm, indicating that point defects within the film impede antiferromagnetic magnon diffusion.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 23.04.2025 - 15:00 CEST

Chiral phononics

Dominik Juraschek, Eindhoven University of Technology

Chiral phononics is an emerging field that utilizes the angular momentum of circularly polarized lattice vibrations to manipulate the properties of quantum materials. When phonons are driven resonantly with an ultrashort circularly polarized terahertz pulse, light makes the ions in the material behave like electromagnetic coils, producing circular motions of the atoms around their equilibrium positions in the crystal. This motion induces real and effective magnetic fields that have been calculated and measured in a range up to the tesla scale, providing a new tool for the control of magnetic order. Here, I provide an introduction to the field and present recent theoretical predictions of novel phenomena arising from chiral phonon driving. These include the light-induced magnetization in antiferromagnets [1] and cavity-engineered phonon chirality [2]. Further, I will show that nonlinear phonon excitation can be utilized to make achiral materials chiral on demand [3].

[1] Kahana, Bustamante Lopez, Juraschek, Science Advances 10, eado0722 (2024)
[2] Yaniv, Juraschek, in preparation
[3] Romao, Juraschek, ACS Nano 18, 29550 (2024)

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 05.02.2025 - 15:00 CET

Spintronics with van der Waals heterostructures

Sergio Valenzuela, ICREA and ICN2

Van der Waals (vdW) heterostructures provide a versatile platform for investigating spintronic phenomena, particularly through their atomically sharp interfaces and tunable properties [1,2]. Such heterostructures allow for the design of proximity effects via short-range interactions, enabling the exploration of spin-orbit coupling and spin-dependent transport in ways not easily achieved with conventional materials [1].
In this talk, I will begin by addressing the importance of boundary states and the quality of the topological insulator (TI)/ferromagnet (FM) interface in maximising spin-orbit torques (SOT). For example, vdW TIs such as (Bi,Sb)2Te3 can influence spin transport and charge-to-spin conversion processes due to spin-momentum locking. I will show how introducing a non-magnetic metallic [3] or, in particular, graphene [4] interlayer between the TI and FM, when the FM is a transition metal, significantly modifies the nature and enhances the efficiency of SOTs [3,4]. Similar enhancements observed with sharp interfaces between TIs and vdW FMs [5] further illustrate the potential of interfacial engineering in shaping spintronic functionalities.
Building on these examples, I will then discuss how proximity effects in graphene can be identified through spin transport dynamics, focusing on our findings on spin relaxation anisotropy [6] and charge-to-spin interconversion [7,8]. I will highlight the role of crystal symmetry, showing how systems with reduced symmetry give rise to diverse spin-orbit fields and unconventional charge-to-spin conversion components, alongside methods for determining their underlying mechanisms. Furthermore, I will demonstrate that electrostatic gating can tune spin relaxation anisotropy, as well as spin Hall and spin galvanic effects, with these phenomena remaining robust up to room temperature [6-8].

[1] J. F. Sierra et al., Nature Nano. 16, 856–868 (2021)
[2] H. Yang, S. O. Valenzuela et al., Nature 606, 663 (2022)
[3] F. Bonell et al., Nano Lett. 20, 5893 (2020)
[4] R. Galceran et al., Adv. Mater. Interfaces 9, 2201997 (2022): T. Guillet, V. Zatko et al., unpublished (2025)
[5] T. Guillet et al., Nano Lett. 24, 822 (2024)
[6] B. Raes et al. Nature Commun. 7, 11444 (2016); L. A. Benítez et al., Nature Phys. 14 (2018); APL Materials 7, 120701 (2019); J. F. Sierra, J. Světlík et al., Nature Mater. (in press 02/2025)
[7] L. A. Benítez et al., Nature Mater. 19, 170 (2020)
[8] L. Camosi et al., 2D Mater. 9, 035014 (2022)

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 11.02.2026 - 15:00 CET

Yossi Paltiel, HUJI

Chiral spintronics technology has the potential to overcome the limitations of other magnetic-based memory technologies and to facilitate the fabrication of inexpensive, high-density memory and other spintronics elements [1]. Recently, by utilizing the CISS effect we demonstrated a simple magnetless spin based magnetic memory [2-5]. When chiral molecules are adsorbed on the surface of thin ferromagnetic film, they induce magnetization perpendicular to the surface (the MIPAC effect) [6].

The MIPAC and chiral-chiral interactions enable to reduce memory size stabilizing chiral spin textures in magnetic thin films by tuning skyrmion properties [7]. Chiral molecules can locally manipulate magnetic properties by inducing magnetization through spin exchange interactions and by creating spin currents. The same effects were demonstrate using non-collinear antiferromagnetic thin films of Mn₃Sn and chiral gating to achieve local, efficient antiferromagnetic memory.

References

[1] See- Hun Yang, Ron Naaman, Yossi Paltiel and Stuart S. P. Parkin, Chiral spintronics, Nature Review Physics 3, 328–343 (2021).

[2] O. Ben Dor, S. Yochelis, S. P. Mathew, R. Naaman, and Y. Paltiel, “A chiral-based magnetic memory device without a permanent magnet” Nature Communications 4, 2256 (2013).

[3] G. Koplovitz, et al. “Magnetic Nanoplatelet-Based Spin Memory Device Operating at Ambient Temperatures” Adv. Mater. 29, 1606748 (2017).

[4] H. Al-Bustami, H. et al. “Single Nanoparticle Magnetic Spin Memristor” Small 14, 1801249 (2018).

[5] H. Al-Bustami, S. Khaldi, O. Shoseyov, S. Yochelis, K. Killi, I. Berg, E. Gross, Y. Paltiel,* and R. Yerushalmi*, “Atomic and Molecular Layer Deposition of Chiral Thin Films Showing up to 99% Spin Selective Transport” Nano Letters 22, 3165-3172 (2022).

[6] O. Ben Dor, S. Yochelis, A. Radko, K. Vankayala, E. Capua A. Capua, S.-H. Yang, L. T. Baczewski, S. S. P. Parkin, I R. Naaman, and Y. Paltiel, “Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field” Nature Communications, 8 14567 (2017).

[7] Yael Kapon, Fabian Kammerbauer, Theo Balland, Shira Yochelis, Mathias Kläui, and Yossi Paltiel, Effects of Chiral Polypeptides on Skyrmion Stability and Dynamics, Nano Letters, 25, 1, 306–312 (2025).

 

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 05.03.2025 - 15:00 CET

On the Origin of Electron-Electron Interactions in Bi2Se3 Topological Thin Films

Bryan J Hickey, University of Leeds

We are using Bi2Se3 as a platform in a number of applications in two large collaborative projects: NAME (Nanoscale Advanced Materials Engineering, https://name-pg.uk) and CAMIE ( Combining Advanced Materials with Interface Engineering https://camie.leeds.ac.uk). In our four-chamber deposition system we grow Bi2Se3 by MBE and transfer the samples under UHV to other chambers where we deposit additional layers such as ferromagnets, antiferromagnets, skyrmion bearing multilayers as well as organic layers such as C60. The groundwork for these projects required a growth campaign to obtain material of world class standard and we have characterised our Bi2Se3 using a wide range of techniques. We have achieved excellent epitaxy using a seed layer of (Bi,In)2Se3 and most of the results there are on layers of 20nm Bi2Se3.
Research into the transport properties of Bi2Se3 has been ongoing for many years but there are still questions to be answered about the nature of the conduction in this interesting material. For example, the spin-orbit lifetime is often assumed to be very short but results can be difficult to interpret when the number of conduction channels is reported to be other than 1 or 2, and frequently, it is less than 1. Equally, the spin-orbit scattering should be independent of temperature but it often cannot be seen to be so in many results. Although several papers have suggested that electron-electron interaction effects are observed in, especially the zero-field low-temperature upturn in the resistivity, the nature and origin of these interactions remains unreported.
We have extracted the lifetime of the spin-orbit interaction (!"), by fitting the full expression of the Hikami, Larkin and Nagaoka (HLN) theory for the MR, which is indeed short in the best materials ~ 10-14 s but can be longer in others. We show that fits to the MR can be achieved with a temperature independent value of !". In the strong spin-orbit limit, the approximate HLN function applies and then the fits return only a single conduction channel. The full analysis allows us to extract the electron-electron interaction time (## )
as a function of temperature and hence determine its origin in terms of Fermi liquid theory
and the effects of a finite mean free path, i.e. ($ ℓ).

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 08.01.2025 - 15:00 CET

Probing 2D Magnetic Materials with magnetotransport

Alberto Morpurgo, University of Geneva

The ability to exfoliate van der Waals crystals of magnetic compounds is giving access to a vast, unexplored family of two-dimensional magnetic materials, with a variety of different magnetic ground states. Most of these compounds are semiconductors that offer –besides the possibility to explore magnetism in highly controlled 2D crystals— a new playground to combine magnetic and semiconducting functionalities. In this talk I will discuss how magnetotransport experiments allow the investigation the magnetic phase diagram of 2D magnetic material down to the ultimate limit of individual monolayers, to reveal phenomena that are difficult –or cannot—be accessed with other existing experimental techniques. After a short introduction, in my talk I will discuss vey recent experiments on field effect transistors realized on exfoliated crystals of CrPS4 –ranging from relatively thick multilayers, to double-gated bilayers, and to individual monolayers– and discuss results that illustrate the wealth of physical phenomena that become accessible with these systems.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 30.10.2024 - 15:00 CET

Quantum Functionalities of Magnetic Skyrmions

Christina Psaroudaki, ENS Paris

In this talk, I will discuss the development of magnetic nano-skyrmions as promising candidates for quantum logic elements, focusing on their potential applications in quantum computing. Nano-skyrmions possess quantized helicity excitations, and quantum tunneling between skyrmions with distinct helicities highlights their quantum nature. By harnessing these unique properties, we propose skyrmion qubits where information is stored in the quantum degree of helicity. Electric and magnetic fields can adjust the logical states of these qubits, offering a versatile operation regime with high anharmonicity.

I will explore the role of electrical control over helicity, opening new pathways for functionalizing collective spin states. Additionally, I will discuss the microwave pulses necessary to generate single-qubit gates and multiqubit schemes that promise scalable architectures with tailored couplings. Scalability, controllability by microwave fields, and nonvolatile readout techniques converge to make skyrmion qubits highly attractive for quantum processors. This talk will highlight the exciting developments, challenges, and potential breakthroughs in quantum magnetism and quantum information using skyrmions.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 27.11.2024 - 15:00 CET

Fractional Charges in 2D magnets & Aharonov-Bohm scattering

Nina del Ser, Caltech

Magnetic skyrmions are characterised by an integer topological charge, Q=1, while merons have half-integer winding numbers, Q=1/2. In this talk, I will describe the physics of magnetic textures with fractional topological charge, which is neither integer nor half-integer. Examples of generic magnetic systems which can host such fractional charges include the meeting points between domains in ferromagnetic films with cubic anisotropy or exploding skyrmions. Only fractionally charged defects give rise to an Aharonov-Bohm effect for incident magnons. We investigate this in a numerical scattering experiment by tracking the magnon-induced forces.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 16.10.2024 - 15:00 CEST

Exploring 3D Spin Structures and Dynamics in Chiral Magnets with Advanced Synchrotron X-ray Techniques

Thorsten Hesjedal, University of Oxford

Recent advances in the study of magnetic skyrmions, topologically protected spin textures, have unlocked new possibilities for innovative low-power, high-speed spintronic devices. This talk presents our recent advancements in using resonant elastic x-ray scattering (REXS) to explore 3D spin structures, such as skyrmions, chiral bobbers, emergent monopoles, and other non-collinear magnetic textures, along with their dynamic behaviors across different timescales.

We have developed cutting-edge 3D REXS techniques [1-4] that enable not only the detailed study of ordered 2D skyrmion lattices but also offer deep insights into microscopic properties like helicity angles and topological winding number [5]. Utilizing circular dichroism REXS (CD-REXS) and the depth sensitivity of soft x-rays, we uncovered surprising long-range surface effects, such as the transformation of Bloch-type skyrmions into Néel-type at the surface of the prototypical chiral magnet Cu2OSeO3 [3,4]. These findings led us to investigate exotic magnetic textures at interfaces in engineered heterostructures, including chiral bobber lattices [6], hybrid skyrmions [7], and the dynamic folding and unfolding of skyrmion strings [8].

The distinctive topology of skyrmions endows them with unique dynamical properties that hold promise for next-generation spintronic devices. In circular magnetic field gradients, skyrmion lattices exhibit controlled rotational dynamics [9]. Most importantly, the role of topological defects is crucial in understanding the slow relaxation dynamics of moving skyrmion lattices, influencing their behavior and stability under external perturbations [10]. On the other hand, understanding the fast, intrinsic magnetization dynamics of skyrmions is crucial for their controlled engineering in high-speed applications. We have pioneered techniques combining ferromagnetic resonance (FMR) with resonant magnetic x-ray reflectivity and diffraction with ferromagnetic resonance (RFMR [11] and DFMR [12]), offering novel pathways for probing real-space spin dynamics and unlocking new opportunities for spintronic device development [13].

[1] S.-L. Zhang et al., Phys. Rev. B 93, 214420 (2016).
[2] S.L. Zhang et al. Phys. Rev. B 96, 094401 (2017).
[3] S.L. Zhang et al., Phys. Rev. Lett, 120, 227202 (2018).
[4] S.L. Zhang et al., Proc. Natl. Acad. Sci. U.S.A. 115, 6386 (2018).
[5] S.L. Zhang et al., Nature Commun. 8, 14619 (2017).
[6] K. Ran et al., Phys. Rev. Lett. 126, 017204 (2020).
[7] K. Ran et al., Nano Lett. 22, 3737 (2022).
[8] H. Jin et al., Nano Lett. 23, 5164 (2023).
[9] S.L. Zhang et al., Nature Commun. 9, 2115 (2017).
[10] H. Jin et al., Nano Lett., in press (2024).
[11] D.M. Burn et al., Phys. Rev. Lett. 125, 137201 (2020).
[12] D.M. Burn et al., Nano Lett. 20, 345 (2020).
[13] G. van der Laan and T. Hesjedal, Nucl. Instrum Methods Phys. Res. B 540, 85 (2023).

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