arXiv subjects

O. Gomonay

Publications and source records attributed to O. Gomonay.

At least 19 recordsLinked to original sources

arXiv2026

Spin-orbit torque-driven synthetic antiferromagnetic oscillator

Antiferromagnets offer a promising route toward robust spintronic devices because of their compensated magnetic order and exchange-enhanced spin dynamics. Here, we demonstrate a spin-orbit torque (SOT)-driven antiferromagnetic oscillator based on a nanoconstriction patterned from a synthetic antiferromagnet (SAF). Spin-rectification spectroscopy reveals electrical excitation of both acoustic and optical SAF eigenmodes, whose field and frequency dependences are quantitatively described by an antiferromagnetic resonance model. In addition to these linear eigenmodes, we observe low-field spin-rectification peaks that emerge only above a threshold DC current near the spin-flop transition. Their current-polarity-dependent sign and locking to an injected RF frequency provide electrical spin-rectification signatures consistent with current-selected chiral self-oscillatory dynamics. Micromagnetic simulations reproduce the threshold excitation of SOT-driven self-oscillations and injection locking, while macrospin simulations predict stable and chaotic nonlinear dynamics within the same spin-flop region. We interpret the multi-peak, weakly RF-frequency-dependent responses as a qualitative signature of complex nonlinear dynamics. These results establish SAF nanoconstrictions as an experimentally accessible platform for studying current-driven antiferromagnetic-like oscillator dynamics and motivate future work on nonlinear spintronic devices for signal processing and reservoir-computing concepts.

cond-mat.mes-hall↗

arXiv2024

Probing nonlinear spin dynamics in canted easy-plane antiferromagnets using spin-rectification effects

We investigate spin-rectification phenomena in canted antiferromagnets, closely connected to the family of altermagnetic materials. Our results show that excitation efficiency is significantly enhanced by the Dzyaloshinskii-Moriya interaction. Antiferromagnetic dynamics can be detected through spin-Hall magnetoresistance and bolometric effects, with an efficiency reaching up to mV/W. The rectified voltage shape is influenced by both the symmetry of the exciting torques, detection mechanisms (continuous spin-pumping and spin-Hall magnetoresistance), and the antiferromagnetic crystalline axis. Under high pumping power, we observe a saturation effect related to Suhl-like spin-wave instabilities and a nonlinear redshift of the antiferromagnetic resonance. These findings open new avenues for studying nonlinear dynamics in antiferromagnetic and altermagnetic spintronic devices.

cond-mat.mes-hall↗

arXiv2024

Structure, control, and dynamics of altermagnetic textures

We present a phenomenological theory of altermagnets, that captures their unique magnetization dynamics and allows modelling magnetic textures in this new magnetic phase. Focusing on the prototypical d-wave altermagnets, e.g. RuO$_2$, we can explain intuitively the characteristic lifted degeneracy of their magnon spectra, by the emergence of an effective sublattice-dependent anisotropic spin stiffness arising naturally from the phenomenological theory. We show that as a consequence the altermagnetic domain walls, in contrast to antiferromagnets, have a finite gradient of the magnetization, with its strength and gradient direction connected to the altermagnetic anisotropy, even for 180$^\circ$ domain walls. This gradient generates a ponderomotive force in the domain wall in the presence of a strongly inhomogeneous external magnetic field, which may be achieved through magnetic force microscopy techniques. The motion of these altermagentic domain walls is also characterized by an anisotropic Walker breakdown, with much higher speed limits of propagation than ferromagnets but lower than antiferromagnets.

cond-mat.mes-hall↗

arXiv2024

Imprinting of Antiferromagnetic Vortex States in NiO-Fe Nanostructures

Magnetic vortices are topological spin structures frequently found in ferromagnets, yet novel to antiferromagnets. By combining experiment and theory, we demonstrate that in a nanostructured antiferromagnetic-ferromagnetic NiO(111)-Fe(110) bilayer, a magnetic vortex is naturally stabilized by magnetostatic interactions in the ferromagnet and is imprinted onto the adjacent antiferromagnet via interface exchange coupling. We use micromagnetic simulations to construct a corresponding phase diagram of the stability of the imprinted antiferromagnetic vortex state. Our in depth analysis reveals that the interplay between interface exchange coupling and the antiferromagnet magnetic anisotropy plays a crucial role in locally reorienting the Néel vector out-of-plane in the prototypical in-plane antiferromagnet NiO and thereby stabilizing the vortices in the antiferromagnet.

cond-mat.mes-hall↗

arXiv2023

Antiferromagnetic magnon spintronic based on non-reciprocal and non-degenerated ultra-fast spin-waves in the canted antiferromagnet α-Fe2O3

Spin-waves in antiferromagnets hold the prospects for the development of faster, less power-hungry electronics, as well as promising physics based on spin-superfluids and coherent magnon-condensates. For both these perspectives, addressing electrically coherent antiferromagnetic spin-waves is of importance, a prerequisite that has so far been elusive, because unlike ferromagnets,antiferromagnets couple weakly to radiofrequency fields. Here, we demonstrate the detection of ultra-fast non-reciprocal spin-waves in the dipolar-exchange regime of a canted antiferromagnet using both inductive and spintronic transducers. Using time-of-flight spin-wave spectroscopy on hematite (α-Fe2O3), we find that the magnon wave packets can propagate as fast as 20 km/s for reciprocal bulk spin-wave modes and up to 6 km/s for surface-spin waves propagating parallel to the antiferromagnetic Neel vector. We finally achieve efficient electrical detection of non-reciprocal spin-wave transport using non-local inverse spin-Hall effects. The electrical detection of coherent non-reciprocal antiferromagnetic spin waves paves the way for the development of antiferromagnetic and altermagnet-based magnonic devices.

cond-mat.mes-hall↗

arXiv2023

Antiferromagnetic insulatronics: spintronics in insulating 3d metal oxides with antiferromagnetic coupling

Antiferromagnetic transition metal oxides are an established and widely studied materials system in the context of spin-based electronics, commonly used as passive elements in exchange bias-based memory devices. Currently, major interest has resurged due to the recent observation of long-distance spin transport, current-induced switching, and THz emission. As a result, insulating transition metal oxides are now considered to be attractive candidates for active elements in novel spintronic devices. Here, we discuss some of the most promising materials systems and highlight recent advances in reading and writing antiferromagnetic ordering. This article aims to provide an overview of the current research and potential future directions in the field of antiferromagnetic insulatronics.

cond-mat.mtrl-sci↗

arXiv2023

Photocurrents, inverse Faraday effect and photospin Hall effect in Mn$_2$Au

Among antiferromagnetic materials, Mn$_2$Au is one of the most intensively studied, and it serves as a very popular platform for testing various ideas related to antiferromagnetic magnetotransport and dynamics. Since recently, this material has also attracted considerable interest in the context of optical properties and optically-driven antiferromagnetic switching. In this work, we use first principles methods to explore the physics of charge photocurrents, spin photocurrents and inverse Faraday effect in antiferromagnetic Mn$_2$Au. We predict the symmetry and magnitude of these effects, and speculate that they can be used for tracking the dynamics of staggered moments during switching. Our calculations reveal the emergence of large photocurrents of spin in collinear Mn$_2$Au, whose properties can be understood as a result of a non-linear optical version of spin Hall effect $-$ which we refer to as the $\textit{photospin Hall effect}$ encoded into the relation between the driving charge and resulting spin photocurrents. Moreover, we suggest that even a very small canting in Mn$_2$Au can give rise to colossal spin photocurrents which are $\textit{chiral}$ in flavor. We conclude that the combination of staggered magnetization with the structural and electronic properties of this material results in a unique blend of prominent photocurrents, which makes Mn$_2$Au a unique platform for advanced optospintronics applications.

cond-mat.mtrl-sci↗

arXiv2022

Antiferromagnetic Hysteresis above the Spin Flop Field

Magnetocrystalline anisotropy is essential in the physics of antiferromagnets and commonly treated as a constant, not depending on an external magnetic field. However, we demonstrate that in CoO the anisotropy should necessarily depend on the magnetic field, which is shown by the spin Hall magnetoresistance of the CoO $|$ Pt device. Below the Néel temperature CoO reveals a spin-flop transition at 240 K at 7.0 T, above which a hysteresis in the angular dependence of magnetoresistance unexpectedly persists up to 30 T. This behavior is shown to agree with the presence of the unquenched orbital momentum, which can play an important role in antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2022

Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin-phonon interactions

Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modelling, two excitation processes of magnetization dynamics in NiO, an off-resonant instantaneous optical spin torque and a strain-wave-induced THz torque induced by ultrafast Pt excitation. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be < 50 fs and > 300 fs, respectively, and thus open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.

cond-mat.mes-hall↗

arXiv2021

Anisotropic long-range spin transport in canted antiferromagnetic orthoferrite YFeO$_3$

In antiferromagnets, the efficient propagation of spin-waves has until now only been observed in the insulating antiferromagnet hematite, where circularly (or a superposition of pairs of linearly) polarized spin-waves propagate over long distances. Here, we report long-distance spin-transport in the antiferromagnetic orthoferrite YFeO$_3$, where a different transport mechanism is enabled by the combined presence of the Dzyaloshinskii-Moriya interaction and externally applied fields. The magnon decay length is shown to exceed hundreds of nano-meters, in line with resonance measurements that highlight the low magnetic damping. We observe a strong anisotropy in the magnon decay lengths that we can attribute to the role of the magnon group velocity in the propagation of spin-waves in antiferromagnets. This unique mode of transport identified in YFeO$_3$ opens up the possibility of a large and technologically relevant class of materials, i.e., canted antiferromagnets, for long-distance spin transport.

cond-mat.str-el↗

arXiv2021

Magnon Transport in the Presence of Antisymmetric Exchange in a Weak Antiferromagnet

The Dzyaloshinskii-Moriya interaction (DMI) is at the heart of many modern developments in the research field of spintronics. DMI is known to generate noncollinear magnetic textures, and can take two forms in antiferromagnets: homogeneous or inter-sublattice, leading to small, canted moments and inhomogeneous or intra-sublattice, leading to formation of chiral structures. In this work, we first determine the strength of the effective field created by the DMI, using SQUID based magnetometry and transport measurements, in thin films of the antiferromagnetic iron oxide hematite, $α$-Fe$_2$O$_3$. We demonstrate that DMI additionally introduces reconfigurability in the long distance magnon transport in these films under different orientations of a magnetic field. This arises as a hysteresis centred around the easy-axis direction for an external field rotated in opposing directions whose width decreases with increasing magnetic field as the Zeeman energy competes with the effective field created by the DMI.

cond-mat.mtrl-sci↗

arXiv2021

Photocurrents of charge and spin in single-layer Fe$_3$GeTe$_2$

In the realm of two-dimensional materials magnetic and transport properties of a unique representative $-$ Fe$_3$GeTe$_2$ $-$ attract ever increasing attention. Here, we use a developed first-principles method for calculating laser-induced response to study the emergence of photo-induced currents of charge and spin in single-layer Fe$_3$GeTe$_2$, which are of second order in the electric field. We provide a symmetry analysis of the emergent photocurrents in the system finding it to be in excellent agreement with ab-initio calculations. We analyse the magnitude and behavior of the charge photocurrents with respect to disorder strength, frequency and band filling. Remarkably, not only do we find a large charge current response, but also predict that Fe$_3$GeTe$_2$ can serve as a source of significant laser-induced spin-currents, which makes this material as a promising platform for various applications in optospintronics.

cond-mat.mes-hall↗

arXiv2021

Ultrafast amplification and non-linear magneto-elastic coupling of coherent magnon modes in an antiferromagnet

We investigate the role of domain walls in the ultrafast magnon dynamics of an antiferromagnetic NiO single crystal in a pump-probe experiment with variable pump photon energy. Analysing the amplitude of the energy-dependent photo-induced ultrafast spin dynamics, we detect a yet unreported coupling between the material's characteristic THz- and a GHz-magnon modes. We explain this unexpected coupling between two orthogonal eigenstates of the corresponding Hamiltonian by modelling the magneto-elastic interaction between spins in different domains. We find that such interaction, in the non-linear regime, couples the two different magnon modes via the domain walls and it can be optically exploited via the exciton-magnon resonance.

cond-mat.other↗

arXiv2021

Readout of a antiferromagnetic spintronics systems by strong exchange coupling of Mn2Au and Permalloy

In antiferromagnetic spintronics, the read-out of the staggered magnetization or Neel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Neel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-estabished read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are retained. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Neel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.

cond-mat.mtrl-sci↗

arXiv2021

Effective strain manipulation of the antiferromagnetic state of polycrystalline NiO

As a candidate material for applications such as magnetic memory, polycrystalline antiferromagnets offer the same robustness to external magnetic fields, THz spin dynamics, and lack of stray field as their single crystalline counterparts, but without the limitation of epitaxial growth and lattice matched substrates. Here, we first report the detection of the average Neel vector orientiation in polycrystalline NiO via spin Hall magnetoresistance (SMR). Secondly, by applying strain through a piezo-electric substrate, we reduce the critical magnetic field required to reach a saturation of the SMR signal, indicating a change of the anisotropy. Our results are consistent with polycrystalline NiO exhibiting a positive sign of the in-plane magnetostriction. This method of anisotropy-tuning offers an energy efficient, on-chip alternative to manipulate a polycrystalline antiferromagnets magnetic state.

cond-mat.mtrl-sci↗

arXiv2020

Direct imaging of current-induced antiferromagnetic switching revealing a pure thermomagnetoelastic switching mechanism

We unravel the origin of current-induced magnetic switching of insulating antiferromagnet/heavy metal systems. We utilize concurrent transport and magneto-optical measurements to image the switching of antiferromagnetic domains in specially engineered devices of NiO/Pt bilayers. Different electrical pulsing and device geometries reveal different final states of the switching with respect to the current direction. We can explain these through simulations of the temperature induced strain and we identify the thermomagnetoelastic switching mechanism combined with thermal excitations as the origin, in which the final state is defined by the strain distributions and heat is required to switch the antiferromagnetic domains. We show that such a potentially very versatile non-contact mechanism can explain the previously reported contradicting observations of the switching final state, which were attributed to spin-orbit torque mechanisms.

cond-mat.mtrl-sci↗

arXiv2020

Magnetoresistance effects in the metallic antiferromagnet Mn$_2$Au

In antiferromagnetic spintronics, it is essential to separate the resistance modifications of purely magnetic origin from other effects generated by current pulses intended to switch the Néel vector. We investigate the magnetoresistance effects resulting from magnetic field induced reorientations of the staggered magnetization of epitaxial antiferromagnetic Mn2Au(001) thin films. The samples were exposed to 60 T magnetic field pulses along different crystallographic in-plane directions of Mn2Au(001), while their resistance was measured. For the staggered magnetization aligned via a spin-flop transition parallel to the easy [110]-direction, an ansiotropic magnetoresistance of -0.15 % was measured. In the case of a forced alignment of the staggered magnetization parallel to the hard [100]-direction, evidence for a larger anisotropic magnetoresistance effect was found. Furthermore, transient resistance reductions of about 1 % were observed, which we associate with the annihilation of antiferromagnetic domain walls by the magnetic field pulses.

cond-mat.mtrl-sci↗

arXiv2019

Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets

The impulsive generation of two-magnon modes in antiferromagnets by femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent longitudinal oscillations of the antiferromagnetic order parameter that cannot be described by a thermodynamic Landau-Lifshitz approach. We argue that this dynamics is triggered as a result of a laser-induced modification of the exchange interaction. In order to describe the oscillations we have formulated a quantum mechanical description in terms of magnon pair operators and coherent states. Such an approach allowed us to} derive an effective macroscopic equation of motion for the temporal evolution of the antiferromagnetic order parameter. An implication of the latter is that the photo-induced spin dynamics represents a macroscopic entanglement of pairs of magnons with femtosecond period and nanometer wavelength. By performing magneto-optical pump-probe experiments with 10 femtosecond resolution in the cubic KNiF$_3$ and the uniaxial K$_2$NiF$_4$ collinear Heisenberg antiferromagnets, we observed coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The detected frequencies as a function of the temperature ideally fit the two-magnon excitation up to the Néel point. The experimental signals are described as dynamics of magnetic linear dichroism due to longitudinal oscillations of the antiferromagnetic vector.

cond-mat.mes-hall↗