Riccardo Tomasello

Politecnico di Bari | Poliba · Dipartimento di Ingegneria Elettrica e dell’Informazione

We have designed a passive spintronic diode based on a single skyrmion stabilized in a magnetic tunnel junction and studied its dynamics induced by voltage-controlled anisotropy (VCMA) and Dzyaloshinskii-Moriya interaction (VDMI). We have demonstrated that the sensitivity (rectified voltage over input microwave power) with realistic physical parame...

Magnetic solitons are promising for applications due to their intrinsic properties such as small size, topological stability, ultralow power manipulation and potentially ultrafast operations. To date, research has focused on the manipulation of skyrmions, domain walls, and vortices by applied currents. The discovery of new methods to control magnet...

Magnetic skyrmions are fascinating topological particle-like textures which are promoted by a trade-off among interfacial properties (perpendicular anisotropy and Dzyaloshinskii-Moriya interaction) and dipolar interactions. Depending on the dominant interaction, complex spin textures, including pure Néel and hybrid skyrmions, have been observed in...

We have designed a passive spintronic diode based on a single skyrmion stabilized in a magnetic tunnel junction and studied its dynamics induced by voltage-controlled anisotropy (VCMA) and Dzyaloshinskii-Moriya interaction (VDMI). We have demonstrated that the sensitivity (rectified voltage over input microwave power) with realistic physical parame...

In the Beyond Moore Law era, with increasing edge intelligence, domain-specific computing embracing unconventional approaches will become increasingly prevalent. At the same time, the adoption of a wide variety of nanotechnologies will offer benefits in energy cost, computational speed, reduced footprint, cyber-resilience and processing prowess. Th...

Skyrmion Hosts An approach to tailor skyrmion‐host materials and magnetic tunnel junctions (MTJs) is proposed by Giovanni Finocchio, Guoqiang Yu, and co‐workers in article number 2200570. The skyrmion in the host material can be successfully imprinted into the free layer of the MTJ and read out via the tunneling magnetoresistance. This work demonst...

Magnetic skyrmions are promising information carriers for dense and energy‐efficient information storage owing to their small size, low driving‐current density, and topological stability. Electrical detection of skyrmions is a crucial requirement to drive skyrmion devices toward applications. The use of a magnetic tunnel junction (MTJ) is commonly...

The static and dynamic properties of skyrmions have recently received increased attention due to the potential application of skyrmions as information carriers and for unconventional computing. While the current-driven dynamics has been explored deeply, both theoretically and experimentally, the theory of temperature gradient-induced dynamics—skyrm...

The development of skyrmionic devices requires a suitable tuning of material parameters to stabilize skyrmions and control their density. It has been demonstrated recently that different skyrmion types can be simultaneously stabilized at room temperature in heterostructures involving ferromagnets, ferrimagnets, and heavy metals, offering a new plat...

The effective control of skyrmion motion is a critical aspect for realizing skyrmion-based devices. Among the potential directions, the use of current induced spin-orbit torque (SOT) is energetically efficient. However, the conventional heavy metals with high crystal symmetry limit the charge-to-spin conversion to the orthogonal configuration, whic...

Voltage-controlled magnetic anisotropy (VCMA) is a low-energy alternative to manipulate the ferromagnetic state, which has been recently also considered in antiferromagnets (AFMs). Here, we theoretically demonstrate that VCMA can be used to excite linear and parametric resonant modes in easy-axis AFMs with perpendicular anisotropy, thus opening the...

Voltage controlled magnetic anisotropy (VCMA) is a low-energy alternative to manipulate the ferromagnetic state, which has been recently considered also in antiferromagnets (AFMs). Here, we theoretically demonstrate that VCMA can be used to excite linear and parametric resonant modes in easy-axis AFMs with perpendicular anisotropy, thus opening the...

In modern building infrastructures, the chance to devise adaptive and unsupervised data-driven structural health monitoring (SHM) systems is gaining in popularity. This is due to the large availability of big data from low-cost sensors with communication capabilities and advanced modeling tools such as deep learning. A promising method suitable for...

We study a vortex in a nanostripe of an antiferromagnet with easy-plane anisotropy and interfacial Dzyaloshinskii-Moriya interaction. The vortex has hybrid chirality, being of Néel type close to its center and of Bloch type away from it. Propagating vortices can acquire velocities up to a maximum value that is lower than the spin wave velocity. The...

Néel skyrmions are generally realized in asymmetric multilayers made of heavy metals (HMs) and ultrathin ferromagnets possessing strong interfacial Dzyaloshinskii-Moriya interactions (iDMIs). Depending on the relative strengths of iDMIs at the interfaces, various types of Néel skyrmions have been suggested, which are typified with characteristicall...

Spintronic technology is emerging as a direction for the hardware implementation of neurons and synapses of neuromorphic architectures. In particular, a single spintronic device can be used to implement the nonlinear activation function of neurons. Here, we propose how to implement spintronic neurons with a sigmoidal and ReLU-like activation functi...

Spintronic technology is emerging as a direction for the hardware implementation of neurons and synapses of neuromorphic architectures. In particular, a single spintronic device can be used to implement the nonlinear activation function of neurons. Here, we propose how to implement spintronic neurons with a sigmoidal and ReLU-like activation functi...

Spintronic diodes are emerging as disruptive candidates for impacting several technological applications ranging from the Internet of things to artificial intelligence. Here, an overview of the recent achievements on spintronic diodes is briefly presented, underlying the major breakthroughs that have led these devices to have the largest sensitivit...

We report a study of the magnetization reversals and skyrmion configurations in two systems - Pt/Co/MgO and Ir/Fe/Co/Pt multilayers, where magnetic skyrmions are stabilized by a combination of dipolar and Dzyaloshinskii-Moriya interactions (DMI). First Order Reversal Curve (FORC) diagrams of low-DMI Pt/Co/MgO and high-DMI Ir/Fe/Co/Pt exhibit stark...

Spintronic diodes are emerging as disruptive candidates for impacting several technological applications ranging from the Internet of Things to Artificial Intelligence. In this letter, an overview of the recent achievements on spintronic diodes is briefly presented, underling the major breakthroughs that have led these devices to have the largest s...

Magnetic skyrmions are emerging as key elements of unconventional operations having unique properties such as small size and low current manipulation. In particular, it is possible to design skyrmion-based neurons and synapses for neuromorphic computing in devices where skyrmions move along the current direction (zero skyrmion Hall angle). Here, we...

Magnetic skyrmions are emerging as key elements of unconventional operations having unique properties such as small size and low current manipulation. In particular, it is possible to design skyrmion based neurons and synapses for neuromorphic computing in devices where skyrmions move along the current direction (zero skyrmion Hall angle). Here, we...

Ferrimagnetic materials (FiMs) represent a promising direction for the realization of spin-based devices since they can combine the ultrafast dynamics typical of antiferromagnets in an easier way to control the magnetic state typical of ferromagnets. In this work, we micromagnetically analyze the magnetization dynamics of a current-driving transiti...

We study a vortex in a nanostripe of an antiferromagnet with easy-plane anisotropy and interfacial Dzyloshinskii-Moriya interaction. The vortex has hybrid chirality being N\'eel close to its center and Bloch away from it. Propagating vortices can acquire velocities up to a maximum value that is lower than the spin wave velocity. When the vortex is...

This chapter deals with the skyrmion dynamics excited by spin-polarized electrical current in different magnetic systems, such as ferromagnets, metallic multilayers as well as synthetic antiferromagnets. We will describe the different origin of a spin-polarized current, which can exert a spin-transfer torque onto the magnetization texture of a skyr...

Antiferromagnetic spintronics is a promising emerging paradigm to develop high-performance computing and communications devices. Antiferromagnetic materials are more abundant than ferromagnets; hence, from a theoretical point of view, it is important to implement simulation tools that can support a data-driven development of materials having specif...

Materials hosting magnetic skyrmions at room temperature could enable compact and energetically-efficient storage such as racetrack memories, where information is coded by the presence/absence of skyrmions forming a moving chain through the device. The skyrmion Hall effect leading to their annihilation at the racetrack edges can be suppressed, for...

We report a study of magnetization reversals and skyrmion configurations in two systems, Pt/Co/MgO and Ir/Fe/Co/Pt multilayers, where magnetic skyrmions are stabilized by a combination of dipolar and Dzyaloshinskii–Moriya interactions (DMIs). The First Order Reversal Curve (FORC) diagrams of low-DMI Pt/Co/MgO and high-DMI Ir/Fe/Co/Pt exhibit stark...

The efficient generation, manipulation and detection of magnetic skyrmions are important for the development of future spintronic devices. One approach is to use electric-current-induced spin torques. Recently, thermally induced skyrmion motion has also been observed, but wider experimental evidence and its capabilities remain limited. Here we repo...

Spin diodes are usually resonant in nature (GHz frequency) and tunable by magnetic field and bias current with performances, in terms of sensitivity and minimum detectable power, overcoming the semiconductor counterpart, i.e., Schottky diodes. Recently, spin diodes characterized by a low-frequency detection (MHz frequency) have been proposed. Here,...

Materials hosting magnetic skyrmions at room temperature could enable new computing architectures as well as compact and energetically efficient magnetic storage such as racetrack memories. In a racetrack device, information is coded by the presence/absence of magnetic skyrmions forming a chain that is moved through the device. The skyrmion Hall ef...

Recent years have witnessed significant progresses in realizing skyrmions in chiral magnets1-4 and asymmetric magnetic multilayers5-13, as well as their electrical manipulation2,7,8,10. Equally important, thermal generation, manipulation and detection of skyrmions can be exploited for prototypical new architecture with integrated computation14 and...

Antiferromagnetic spintronics is a promising emerging paradigm to develop high-performance computing and communications devices. From a theoretical point of view, it is important to implement simulation tools that can support a data-driven development of materials having specific properties for particular applications. Here, we present a study focu...

Spin-diodes are usually resonant in nature (GHz frequency) and tuneable by magnetic field and bias current with performances, in terms of sensitivity and minimum detectable power, overcoming the semiconductor counterpart, i.e. Schottky diodes. Recently, spin diodes characterized by a low frequency detection (MHz frequency) have been proposed. Here,...

While antiferromagnetic skyrmions display appealing properties, their lateral expansion in the high-velocity regime hinders their potential for applications. In this work, we study the impact of spin Hall torque, spin transfer torque, and topological torque on the velocity-current relation of antiferromagnetic skyrmions with the aim of reducing thi...

We introduce a formulation of a two-sublattice micromagnetic model, which can describe the statics and dynamics of ferromagnets, antiferromagnets, and ferrimagnets. Such a formulation is based on the normalization of exchange, Dzyaloshinskii–Moriya interaction, and anisotropy parameters with respect to the square modulus of the saturation magnetiza...

In modern building infrastructures, the chance to devise adaptive and unsupervised data-driven health monitoring systems is gaining in popularity due to the large availability of data from low-cost sensors with internetworking capabilities. In particular, deep learning provides the tools for processing and analyzing this unprecedented amount of dat...

The study of thermodynamics of topological defects is an important challenge to understand their underlying physics. Among them, magnetic skyrmions have a leading role for their physical properties and potential applications in storage and neuromorphic computing. In this paper, the thermodynamic statistics of magnetic skyrmions is derived. It is sh...

The study of thermodynamics of topological defects is an important challenge to understand their underlying physics. Among them, magnetic skyrmions have a leading role for their physical properties and potential applications in storage and neuromorphic computing. In this paper, the thermodynamic statistics of magnetic skyrmions is derived. It is sh...

The study of thermodynamics of topological defects is an important challenge to understand their underlying physics. Among them, magnetic skyrmions have a leading role for their physical properties and potential applications in storage and neuromorphic computing. In this paper, the thermodynamic statistics of magnetic skyrmions is derived. It is sh...

The study of thermodynamics of topological defects is an important challenge to understand their underlying physics. Among them, magnetic skyrmions have a leading role for their physical properties and potential applications in storage and neuromorphic computing. In this paper, the thermodynamic statistics of magnetic skyrmions is derived. It is sh...

We present a study of the stability of room-temperature skyrmions in [Ir/Fe/Co/Pt] thin film multilayers, using the First Order Reversal Curve (FORC) technique and magnetic force microscopy (MFM). FORC diagrams reveal irreversible changes in magnetization upon field reversals, which can be correlated with the evolution of local magnetic textures pr...

Room temperature magnetic skyrmions in magnetic multilayers are considered as information carriers for future spintronic applications. Currently, a detailed understanding of the skyrmion stabilization mechanisms is still lacking in these systems. To gain more insight, it is first and foremost essential to determine the full real‐space spin configur...

Nonlinear dynamics has been the key ingredient to improve the performance, in terms of sensitivity, of biased resonant spintronic diodes beyond their semiconductor counterparts. We experimentally demonstrate a nonlinear regime broadband detection for nanoscale spintronic diodes (NSD) where the rectification properties are independent of the input m...

The understanding of the dynamical properties of skyrmions is a fundamental aspect for the realization of a competitive skyrmion based technology beyond complementary metal-oxide semiconductors. Most of the theoretical approaches are based on the approximation of a rigid skyrmion. However, thermal fluctuations can drive a continuous change of the s...

The understanding of the dynamical properties of skyrmion is a fundamental aspect for the realization of a competitive skyrmion based technology beyond CMOS. Most of the theoretical approaches are based on the approximation of a rigid skyrmion. However, thermal fluctuations can drive a continuous change of the skyrmion size via the excitation of th...

A strategy to drive skyrmion motion by a combination of an anisotropy gradient and spin-Hall effect has recently been demonstrated. Here, we study the fundamental properties of this type of motion by combining micromagnetic simulations and a generalized Thiele's equation. We find that the anisotropy gradient drives the skyrmion mainly along the dir...

Recently discovered exotic magnetic configurations, namely magnetic solitons appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya Interaction (i-DMI), have excited scientists to explore their potential applications in emerging spintronic technologies such as race-track magnetic memory, spin logic, radio frequency nano-oscillators...

Pulse-compression thermography is an emerging non-destructive technique whose effectiveness strictly depends on the choice of the coded excitations used to modulate the heating stimulus. In this paper, the features of frequency-modulated coded signals, i.e., chirps, have been tested for imaging thin Teflon defects embedded within a carbon fiber com...

A strategy to drive skyrmion motion by a combination of an anisotropy gradient and spin Hall effect has recently been demonstrated. Here, we study the fundamental properties of this type of motion by combining micromagnetic simulations and a generalized Thiele equation. We find that the anisotropy gradient drives the skyrmion mainly along the direc...

The recent technological realization of perpendicular magnetic tunnel junction (MTJ) with two reference layers has opened a new route for scaling the overall size of spin-transfer torque MRAM. This is because for an antiparallel configuration of the magnetization of the reference layers the two spin-transfer torques add each other constructively gi...

The current-driven domain wall motion along two exchange-coupled ferromagnetic layers with perpendicular anisotropy is studied by means of micromagnetic simulations and compared to the conventional case of a single ferromagnetic layer. Our results, where only the lower ferromagnetic layer is subjected to the interfacial Dzyaloshinskii-Moriya intera...

The harvesting of ambient radio-frequency (RF) energy is an attractive and clean way to realize the idea of self-powered electronics. Here we present a design for a microwave energy harvester based on a nanoscale spintronic diode (NSD). This diode contains a magnetic tunnel junction with a canted magnetization of the free layer, and can convert RF...

In this paper, a variation-aware simulation framework for hybrid circuits comprising MOS transistors and magnetic tunnel junction (MTJ) devices is presented. The framework is based on one-time characterization via micromagnetic multi-domain simulations, overcoming the inaccuracies introduced by single-domain analysis, which most of the existing fra...

Understanding the physical properties of magnetic skyrmions is important for fundamental research with the aim to develop new spintronic device paradigms where both logic and memory can be integrated at the same level. Here, we show a universal model based on the micromagnetic formalism that can be used to study skyrmion stability as a function of...

A storage scheme based on racetrack memory, where the information can be coded in a domain or a skyrmion, seems to be an alternative to conventional hard disk drive for high density storage. Here, we perform a full micromagnetic study of the performance of synthetic antiferromagnetic (SAF) racetrack memory in terms of velocity and sensitivity to de...

The technological implementation of STT-MRAMs in real devices needs a complete description of the statistical switching behavior at room temperature. In this work, we investigate, by means of a full micromagnetic model, the effect of the interfacial Dzyaloshinskii–Moriya Interaction (IDMI) on the critical current density and probability density fun...

This paper proposes a protocol for the electrical detection of a magnetic skyrmion via the change of the tunneling magnetoresistive (TMR) signal in a three-terminal device. This approach combines alternating spin-transfer torque from both spin-filtering (due to a perpendicular polarizer) and spin-Hall effect with the TMR signal. Micromagnetic simul...