Bert Koopmans
Towards photonic-spintronic integration
TU Eindhoven, The Netherlands
Advanced, versatile and energy efficient information and communication technologies will most definitely require hybrid solutions. While within BeMagic the focus is on combining spintronic and electronic control using magnetelectronic materials, this presentation will address the opportunities for the integration of spintronics with photonics. Novel schemes for controlling the ferromagnetic state at femtosecond time scales by pulsed laser excitation have received great interest. By driving systems into the strongly non-equilibrium regime, it has been shown possible not only to quench magnetic order, but also to switch the magnetization by single laser pulses – so-called all-optical switching (AOS). In parallel, it has been found that pulsed laser excitation can also induce spin currents over several to tens of nanometers, which can act as an additional source of sub-picosecond magnetization dynamics. Thereby, a scientifically exciting link between the fields of ‘femtomagnetism’ and spintronic transport physics has emerged. Moreover, it is being envisioned that combining the two fields could pave the way to a new class of hybrid spintronic-photonic devices, in which data is copied between photonic and magnetic (spintronic) domain without any intermediate electronic steps, leading to ultrafast and highly energy-efficient IT solutions.
In this presentation, some of the underlying phenomena will be addressed, and recent progress on scientific issues that are considered key for realizing the envisioned technology will be discussed. Examples of progress towards integrated spintronic-photonic devices will be presented, including current-induced domain wall motion in Pt/Co/Gd-based conduits that display efficient AOS [1] with domain-wall velocities over 2000 m/s [2], AOS of MTJs [3], as well as on-chip magneto-optical reading of 300 x 400 nm2 magnetic elements structured on top of InP photonic waveguides [4]. Finally, to further reduce the device footprint and increase data densities, near-field plasmonic approaches will be in inevitable. Recent device simulations on using photonic cavities and plasmonic nano-antennas for sub-diffraction limited optical writing and reading [5] provide inside into pushing the ultimate performance.
References:
[1] M.L.M. Lalieu et al., Nature Commun. 10, 110 (2019).
[2] P. Li, T. Kools, et al., Adv. Electron. Mater. 2200613 (2022).
[3] L. Wang et al., PNAS 119, e2204732119 (2022).
[4] F.E. Demirer, et al., Nanophotonics 11, 3319 (2022).
[5] H. Pezeshki, P. Li et al., Phys. Rev. Applied 19, 054036 (2023).
Minsoo Kim
Superelastic and shape-memory magnetoelectric nanocomposites
ETH Zürich, Switzerland
Nanoscale brings distinguished phenomena which are not foreseen in bulk nature. This presentation covers the remarkable mechanical and magnetoelectric (ME) properties exhibited by nanoscale ME thin films. Our research focuses on the development of a composite thin film composed of barium titanate and cobalt ferrite bilayers, grown epitaxially using pulsed laser deposition. The interfacial stress generated within this bilayer system gives rise to the formation of freestanding structures, including helices, dog-bones, and kirigami patterns. These three-dimensional ME structures showcase superelasticity and shape memory characteristics. Furthermore, we successfully transfer these structures onto flexible PDMS substrates, thereby demonstrating a strain-sensitive magnetoelectric coupling coefficient. The potential applications of these ME nanocomposites extend to diverse fields, such as microrobotics, soft robotics, and flexible electronics.
Jon Ander Arregi
Imaging magnetic phase coexistence in spatially confined metamagnets
CEITEC, Brno, Czech Republic
Interconnection among order parameters in first-order phase transitions typically leads to complex behavior of phase separated states that is highly dependent on both intrinsic (e.g., symmetry, magnetic exchange) and extrinsic factors (e.g., strain, disorder). These ingredients provide rich opportunities for making designer materials for applications in energy conversion, magnetoelastic actuation, and low-power electronic devices. Here, we focus on the close-to-room-temperature phase transition from antiferromagnetic to ferromagnetic order in the FeRh alloy, a prototype metallic system showing interconnected structural, magnetic, and electronic order. We employ different magnetic imaging techniques in spatially confined FeRh systems – ranging from thin films to patterned and self-assembled nanostructures – to explore the nature of phase coexistence, finding that its presence and character are susceptible to parameters such as nucleation sites, lateral confinement, morphology, applied magnetic field, and strain. In the presentation, we discuss strategies to control magnetic phase coexistence in FeRh in small length scales and ultrafast time scales.
Emma Chiaramello
Magnetoelectric nanostructures for neural modulation: a computational framework
CNR IEIIT, Italy
Magnetoelectric nanostructures have recently attracted a great research attention thanks to their capability of inducing a local electric potential upon an applied magnetic field and vice versa. This behavior opens the possibility of using them as multifunctional devices in various biomedical applications, including neural system stimulation. In this talk, various aspects related to the application of magnetoelectric nanostructures for stimulating both peripheral and central nervous system will be presented. Various computational approaches will be explored and combined towards the assessment of the feasibility of using these nanotechnologies for developing highly innovative neural interfaces, towards a completely new neural system stimulation paradigm.
Kristen Kozielski
Magnetoelectric nanomaterials for wireless neuronal modulation
TU Munich, Germany
Prof. Kristen Kozielski works with new materials for wireless communication with the brain and nervous system. Her research focuses on understanding and optimizing materials for controlled, electronic signaling to and from the brain. The goal of this work is to contribute to neurotechnologies that are minimally invasive, and possibly implanted with no surgical intervention. Her multidisciplinary group works in materials science, biomaterials, nanotechnology, electrical engineering, and neurobiology.
Ivan Soldatov
Kerr microscopy for domain imagining
IFW Dresden, Germany
The study of magnetic domains, being the basic elements of the magnetic
microstructure of magnetically ordered materials, is essential for a comprehensive
understanding of magnetization reversal processes from both, a fundamental as well as from an application point of view. After the introduction of digital image processing in the 1980s, wide-field Kerr microscopy has become a widely used and effective tool for magnetic domain imaging providing the most direct access to the effective magnetic properties of materials from macro- down to the nanoscale.
Here, I focus on recent advances in wide-field magneto-optical Kerr microscopy for
the imaging of magnetic microstructures. The advanced techniques include selective
sensitivity, quantitative domain analysis, ways for microscopy beyond the resolution limit will be addressed as well.
Both fundamental and technical aspects of wide-field Kerr microscopy will be considered. Starting with basics of in-plane and out-of-plane Kerr contrast formation in the microscope and conventional applications like MOKE magnetometery or depth sensitive Kerr microscopy we will proceed to advanced techniques applied in Kerr microscopy including selective sensitivity, quantitative domain analysis and first order reversal curve (FORC) analysis. Quantitative and computing ways for microscopy beyond the resolution limit will be addressed as well. The not-on-sample-direct Kerr microscopy with help of magneto-optical indicator film (MOIF) together with other techniques will be discussed.
Marco Coïsson
Nanomaterials characterisation through magnetic field dependent atomic force microscopy
INRIM, Italy
Magnetic nanomaterials are the subject of intense research because of their applications in information technology, environment and biomedicine. However, the magnetic properties of materials are strongly affected by either physical (e.g. nanocrystals, anisotropy) or geometry (e.g. patterning) variations at length scales in the 100 nm – 100 µm range. Characterising the magnetic properties of materials at such scales requires innovative approaches and the combination of experimental and numerical methods.
A powerful approach for the nanoscale characterisation of magnetic nmaterials is offered by magnetic force microscopy (MFM), which is a technique derived by atomic force microscopy (AFM) exploiting a magnetically coated tip that interacts with the magnetisation of the underlying sample. While conventional MFM is used as a domains imaging technique, its extension to variable applied magnetic field conditions [1-3] allows to open new possibilities for exploring the magnetic properties of materials at the sub micrometric scale.
In Figure 1, a few examples of characterisations exploiting magnetic field dependent MFM are reported. In Figure 1(a) the field evolution of the phase contrast of the MFM is shown for a magnetic dot, whose local hysteresis loop is reconstructed, with very high magnetic field resolution, in Figure 1(b) for two cases with opposite vortex magnetisation chirality. In Figure 1(c) the technique is exploited to investigate the microscopic origin of the rotatable anisotropy in magnetic materials displaying weak stripe domain configuration. The variable magnetic field MFM provides a versatile framework that can be extended and generalised, one additional example being the possibility to measure magnetostriction on thin films.
In this presentation, the magnetic field dependent AFM / MFM will be introduced and some results of magnetic materials characterisation at the sub-micrometric scale will be discussed.
Figure 1: (a) Magnetic field evolution of the phase signal of an MFM; at the bottom, the profile along the dashed line is reported. (b) Reconstructed local hysteresis loops from fielddependent MFM data, for magnetic dots, with two opposite chirality states. (c) Magnetic stripes rotation under application of a magnetic field, and comparison with vector VSM measurements of the magnetisation.
References:
[1] M. Coïsson, G. Barrera, F. Celegato, E. Enrico, A. Manzin, E.S. Olivetti, P. Tiberto, F. Vinai, J. Phys. D: Appl. Phys. 47 (2014) 325003
[2] M. Coïsson, G. Barrera, F. Celegato, A. Manzin, F. Vinai, P. Tiberto, Sci. Rep. 6 (2016) 29904
[3] M. Coïsson, W. Hüttenes, M. Cialone, G. Barrera, F. Celegato, P. Rizzi, Z.H. Barber, P. Tiberto, Appl. Surf. Sci. 525 (2020) 146514
Karin Leistner
Strategies for the electrodeposition of ultrathin magnetic films and nanostructures
TU Chemnitz, Germany
Electrodeposition is an efficient room-temperature synthesis method for magnetic films and nanostructures with potential applications in nanomagnetic and spintronic devices and catalysis. For a defined electrochemical synthesis at the nanoscale, the understanding of the underlying electrode processes is decisive. This is especially challenging when ferromagnetic metals (Co, Fe and Ni) and their alloys are electrodeposited, because the complexity of the processes at the solid/liquid interface increases with the superposed hydrogen evolution reaction. In the last decades, significant progress has been made towards the electrochemical deposition of high-quality ultrathin films and nanostructures with defined composition, epitaxy, and morphology, which can compete with structures prepared by vacuum techniques. In my talk I will give an overview on recent advances in this field, and discuss specific examples for self-terminating and epitaxial nanoelectrodeposition.[1,2] The focus will lie on a discussion of the underlying mechanisms and the tuning of the magnetic properties.
References:
[1] Nichterwitz et al., Electrochimica Acta 2022, 415, 140170
[2] S. Guo et al., Nano Lett. 2022, 22, 4006
Shimpei Ono
Development of iontronics
CRIEPI, Japan
Electric field control of charge carrier density has long been a key technology to tune the physical properties of condensed matter, exploring the modern semiconductor industry. One of the big challenges is to increase the maximum attainable carrier density, however it is limited by the quality of gate dielectrics. In this talk, I’m going to show the novel technique to modulate carrier density making use of ionic liquid electrolytes. With electrolyte gating, we can modulate up to 10^15/cm2 of carrier density at the interface which is 2 orders of magnitude larger than conventional gate dielectrics and demonstrate that we can indeed control electric properties as well as magnetic properties by electric-field effect doping.
Paola Rizzi
Unoversità de Torino, Italy
Pending abstract
Shinbuhm Lee
Hydrogen control of double exchange interaction in La0.67Sr0.33MnO3 for ionic-electric magnetic coupled applications
DGIST, Republic of Korea
Dynamic tuning of ion concentrations has attracted significant attention for creating materials’ versatile functionalities which was impossible by classical control knobs. Despite of these merits, the fundamental questions, how ions affect the electronic bandstructure and how ions simultaneously change electrical and magnetic properties, still remain. Here, by annealing platinum-dotted La0.67Sr0.33MnO3 (LSMO) films in hydrogen and argon at a lower temperature of 200°C for several minutes, we achieve a reversible change in resistivity by three orders of magnitude with tailored ferromagnetic magnetization. We suggest that the transition occurs via tuning of double exchange interaction, ascribed to electron-doping-induced and/or lattice-expansion-induced modulation of the double exchange interaction, along with an increase in the hydrogen concentration. High reproducibility, long-term stability, and linear multilevel appeal for ionic-electric-magnetic coupled applications.
Kerem Camsari
UC Santa Barbara, USA
Pending abstract
Jordi Sort
Magneto-ionics for neuromorphic computing
UAB, Spain
Manipulating magnetism with voltage has an enormous potential to boost energy efficiency in nanoscale device applications since Joule heating effects associated with flowing electric current (needed to generate magnetic fields) are minimized. We have recently demonstrated the possibility to induce considerable reversible, non-volatile changes in the magnetic properties (coercivity, magnetic moment) of nanoporous films consisting of metal alloys (e.g., CuNi, FeCu) or oxides (e.g., FeOx , CoFe2O4 ), by applying an electric field through a liquid electrolyte gate at room temperature [1,2]. In turn, we have made progress in the field of magneto-ionics, i.e., voltage-driven ion transport in magnetic materials, which has traditionally relied on controlled migration of oxygen or lithium ions. Here, I will show that voltage-driven transport of nitrogen ions can be triggered at room temperature in transition metal nitride (CoN, FeN) films via liquid electrolyte gating [3,4]. Nitrogen magneto-ionics can induce reversible ON-OFF transitions of ferromagnetic states at faster rates and lower threshold voltages than oxygen magneto-ionics. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. Remarkably, and in contrast to oxygen magneto-ionics, nitrogen transport occurs uniformly through a plane-wave-like migration front, without the assistance of diffusion channels, particularly interesting for the implementation of multi-stack memory devices. Furthermore, I will show that nitrogen magneto-ionics can be used to emulate some important neuromorphic functionalities. By cumulative effects of DC and pulsed voltage actuation (at frequencies in the range 1 – 100 Hz), learning, memory retention, forgetting and self-learning by maturity (post-stimulated learning) can be mimicked. This latter effect can serve as a logical function for the device to decide between self-learning or forgetting emulation, at will, without any additional electric voltage input. This constitutes a novel approach to emulate some specific neural functionalities (e.g., learning under deep sleep), that are challenging to achieve using other classes materials currently employed for neuromorphic computing applications.
References:
[1] A. Quintana et al., Adv. Funct. Mater. 27 (2017) 1701904.
[2] C. Navarro-Senent et al., APL Mater. 7 (2019) 030701.
[3] J. de Rojas et al., Nat. Commun. 11 (2020) 5871.
[4] J. de Rojas et al, ACS Appl. Mater. Interfaces 13 (2021) 30826–30834.
Srdjan Stavric
The interlayer coupling of two-dimensional magnets
CNR-SPIN, Italy
The discovery of truly two-dimensional (2D) ferromagnetism in monolayer CrI3
ended the long lasting pursuit for 2D magnets and opened a new stage in the research of 2D materials. With 2D magnets at our disposal, if one starts to think further towards the construction of real devices that will harness their properties the question that arises is how the two 2D magnets couple with each other. Here the interlayer exchange coupling emerges as an important player in the game. To make the things more interesting, recent studies suggest that the interlayer exchange coupling is much more important than previously expected. For example, bilayer CrI3 is known to possess two different structural phases – rhombohedral and monoclinic – with the stacking sequence of layers being their only difference. Yet, this structural difference is sufficient for the two structures to display disparate magnetic properties, with the first being the ferromagnet and the second layered antiferromagnet.
The subject of our study is the interlayer exchange interaction in bilayer CrI3. We combine the density functional theory calculations (DFT) with Hamiltonian modelling and develop a computational procedure that enables the calculation of the exchange matrices with the μeV accuracy. Starting with microscopic description and ending with fully magnetized layers, we examine the interlayer anisotropic exchange in bilayers with rhombohedral and monoclinic stacking sequences. We find a considerable interlayer Dzyaloshinskii-Moriya (DM) between the sublattices of monoclinic bilayer. Importantly, our finding demonstrates the ability of iodine ligands to efficiently mediate the interlayer DM interaction across the van der Waals gap of this semiconducting bilayer. The strength of interlayer DMI is similar to that observed in metallic thin films, where the conduction electrons of Pt spacer are those that mediate the DM interaction between ferromagnetic multilayers with perpendicular magnetizations. In addition, we show that the single-ion anisotropy, which is usually perceived as the magnetic property inherent of monolayer, largely depends on stacking and increases by 50% from monoclinic to rhombohedral stacking. Our study gives promise that magnetic bilayers containing ligands which feature strong spin-orbit coupling can be used to achieve the chiral control of spin textures.
Baishun Yang
Moiré Magnetic Exchange Interactions in Twisted Magnets
CNR-SPIN, Italy
Moiré superlattices, which serves as ideal platforms to host fascinating properties and create intriguing applications, can be constructed by stacking two van der Waals (vdW) layered materials with a relatively small twist angle (θ). Such a twist angle offers a new degree of freedom to effectively modulate the fundamental electronic structures, providing an exotic approach to generate and manipulate many new physical phenomena in different 2D vdW systems. These exciting advances are introducing a brand-new research area in condensed matter physics, i.e., twistronics. Recently, many efforts are made to bring the vdW magnets into twistronics. In twisted BL-CrI3 (tBL-CrI3) with small θ, the unexpected spin textures with nonzero remanent magnetization can appear forming hexagonal patterns, raising puzzles on its origin.
Here, we develop a microscopic moiré spin Hamiltonian that enables the effective description of MMEIs via a sliding-mapping approach in twisted magnets, as demonstrated in twisted bilayer CrI3. Unexpectedly, we discover that the emergence of MMEIs can create an unprecedented magnetic skyrmion bubble (SkB) with non-conversed helicity, named as moiré- type SkB, representing a unique spin texture solely generated by MMEIs and ready to be detected under the current experimental conditions. Importantly, the size and population of SkBs can be finely controlled by twist angle, a key step for skyrmion-based information storage. Furthermore, we reveal that the MMEIs can be effectively manipulated by the substrate-induced interfacial Dzyaloshinskii-Moriya interaction, modulating the twist-angle-dependent magnetic phase diagram, which solves the outstanding disagreements between prior theories and experiments.
References:
1. Andrei, E. Y. & MacDonald, A. H. Nat. Mater. 19, 1265-1275 (2020). 2. Kennes, D. M. et al. Nat. Phys. 17, 155-163 (2021).
3. Song, T. et al. Science 374, 1140-1144 (2021).
4. Xu, Y. et al. Nat. Nanotechnol. 17, 143-147 (2022).
5. Baishun Yang, et al. arXiv:2211.15186 (in press).
