Spin Dynamics Research Articles

Modulation of Spin and Lattice Dynamics by Thickness Control of Tb in Si/CoFe/Tb/Al Thin Films

Modulation of Spin and Lattice Dynamics by Thickness Control of Tb in Si/CoFe/Tb/Al Thin Films

Room Temperature Relaxometry of Single Nitrogen Vacancy Centers in Proximity to α-RuCl3 Nanoflakes.

Nitrogen vacancy (NV) center-based magnetometry has been proven to be a versatile sensor for various classes of magnetic materials in broad temperature and frequency ranges. Here, we use the longitudinal relaxation time T1 of single NV centers to investigate the spin dynamics of nanometer-thin flakes of α-RuCl3 at room temperature. We observe a significant reduction in the T1 in the presence of α-RuCl3 in the proximity of NVs, which we attribute to paramagnetic spin noise confined in the 2D hexagonal planes. Furthermore, the T1 time exhibits a monotonic increase with an applied magnetic field. We associate this trend with the alteration of the spin and charge noise in α-RuCl3 under an external magnetic field. These findings suggest that the influence of the spin dynamics of α-RuCl3 on the T1 of the NV center can be used to gain information about the material itself and the technique to be used on other 2D materials.

Chiral spin textures creation and dynamics in a rectangular nanostructure

Abstract Controlled creation of stable chiral spin textures is required to use them as an energy-efficient information carrier in spintronics. Here we have studied the stable creation of isolated chiral spin texture (skyrmion and antiskyrmion) and its pair through the magnetization reversal of a rectangular nanostructure using spin-polarized currents. An isolated spin texture is created through a negative current pulse. Dynamics of the stable spin texture are explored under external magnetic fields, and the resonant frequencies are calculated. A stable skyrmion pair is created using an asymmetric current pulse, and their interaction is studied using the Thiele equation. The stability of isolated or paired spin texture depends on the Dzyaloshinskii–Moriya interaction strength, spin-polarized current density, and pulse duration. In addition, the stability of the skyrmion pair depends on their initial separation, and a threshold for the separation between skyrmions of 78 nm is observed.

All-Electrical Readout of Coherently Controlled Spins in Silicon Carbide.

Spin defects in silicon carbide are promising candidates for quantum sensing applications as they exhibit long coherence times even at room temperature. However, spin readout methods that rely on fluorescence detection can be challenging due to poor photon collection efficiency. Here, we demonstrate coherent spin control and all-electrical readout of a small ensemble of spins in a SiC junction diode using pulsed electrically detected magnetic resonance. A lock-in detection scheme based on a three stage modulation cycle is implemented, significantly enhancing the signal-to-noise ratio. This technique enabled observation of coherent spin dynamics, specifically Rabi spin nutation, spin dephasing, and spin decoherence. The use of these protocols for magnetometry applications is evaluated.

Spin-wave-driven tornado-like dynamics of three-dimensional topological magnetic textures

The abundant topological magnetic textures in three-dimensional systems provide opportunities to investigate the fundamental spin dynamics and realize spintronic applications. The dynamics of such magnetic textures have however rarely been studied, especially for those driven by spin waves, which allow applications with ultralow energy consumption and ease of implementation even in insulating systems. Here, we report our micromagnetic simulations on the spin-wave-driven dynamics of a skyrmion tube (SkT) and chiral bobber (ChB) in a thick magnetic film. We predict tornado-like dynamics in both SkT and ChB, where the topological centers present a lateral rotation with the rotation centers forming a distorted profile in the thickness direction. While the velocity of SkT scales with the driving power, the ChB motion presents a threshold in the driving field, which is found to depend linearly on its penetration length. This distinct behavior could be useful to differentiate ChB from SkT and estimate its penetration length experimentally.

Magneto‐Optical Interactions in Layered Magnets

AbstractThe rapidly emerging field of 2D magnetic materials has garnered significant attention due to its fascinating physical properties and wide‐ranging potential applications. This review highlights the importance of magneto‐optical interactions as a crucial tool for both studying and modulating 2D magnets. It offers a comprehensive survey of current research concerning magneto‐optical interactions in 2D magnetic materials, encompassing the magneto‐optical Kerr effect, reflection magnetic circular dichroism, second‐harmonic generation, photoluminescence, inelastic light scattering, and time‐resolved spectroscopy. This review discusses how these techniques provide insights into the properties of 2D magnets, enabling exploration of magnetic phase transitions, lattice alterations, spin dynamics, as well as their responses to external fields. Moreover, it emphasizes the modulation of magnetic properties by photo‐stimulation and offers a brief outlook on this swiftly developing field.

Study on microscopic origin of spin excitation in TmFeO3 by time-resolved multicolor optical pump-probe spectroscopy

Spin dynamics of TmFeO3, mainly induced by two different mechanisms, were investigated by time-resolved multicolor pump-probe spectroscopy using femtosecond laser pulses. The spin dynamics, caused either by spin-reorientation phase transition or optical polarization-dependent effect, were distinguished by investigating their dependencies on external magnetic field and optical polarization. Spectral-dependent magneto-optic studies of the spin phase transition-induced spin dynamics revealed that laser-induced nonthermal exchange interaction between the electron states of iron (Fe3+) and thulium (Tm3+) ions is crucial for subsequent spin dynamics. This exchange interaction is influenced by the population change of the 4f electron states of Tm3+ ions, making the spin wave generation highly dependent on crystal temperature. However, spectroscopic studies of the polarization-dependent spin dynamics show that they are only related to the 3d electrons of Fe3+ ions, therefore, the spin dynamics appear to be a universal effect over a wide temperature range. Our observation can be further applied to study extended orthoferrite systems with other rare earth atoms.

Filamentary velocity scaling validation and spin dynamics in the DIII-D tokamak

Measured filament velocities in the DIII-D tokamak are compared against theoretical scalings, finding that the latter often represents an upper limit on experimental velocity distributions with most filaments possessing lower velocity. Filament spin from internal E × B drift is experimentally demonstrated to alter filament radial velocity. A critical spin velocity, where filament radial velocity peaks, is observed and corresponds to approximately 5 km/s. This transition is corroborated using a less direct measure of filament spin in the form of a temperature ratio. These techniques are combined to find that the critical spin velocity closely aligns with transport times along and across filaments becoming comparable. The normalized filament size distribution is consistent with the most stable size as dictated by Kelvin–Helmholtz and curvature-driven instabilities. Overall, the findings suggest filament stability and spin alter filamentary transport that may threaten the integrity of first walls in fusion devices.

Spin–orbit coupling effects on localization and correlated tunneling for two interacting bosons in a double-well potential

We theoretically study the tunneling dynamics of two interacting spin–orbit-coupled (SOC) atoms trapped in a periodically perturbed double-well potential. We find that the phenomenon of coherent destruction of tunneling (CDT) can exist only for certain values of SOC, and two different mechanisms for the appearance of CDT are identified in this system. One is the conventional CDT resulting from quasi-energy degeneracy, while the other CDT originates from the dark Floquet state with zero quasi-energy for all values of the driving parameters. We discover that under double modulation combining the double-well potential shaking and a time-periodic Zeeman field, it is possible to realize spin-flipping single-atom Rabi tunneling and the CDT induced by the dark Floquet state at any value of SOC strength, which is not accessible with a single-drive field. Furthermore, we show that the detuning of Zeeman field with respect to the multiphoton energy is particularly significant in the case of the correlated two-particle tunneling mediated by SOC. We expect that these results will stimulate further exploration of the many-body dynamics in the interacting systems and expand the possibilities for manipulating the spin dynamics.

Density Functional Waltz: Molecular Theory of Spin Dynamics

Spin dynamics in molecular systems lies at the heart of contemporary research, promising revolutionary applications in fields like spintronics and quantum information processing. The paper provides insights into green techniques to improve spin dynamics for utilization in quantum computing and magnetic materials. This dynamic approach describes the temperature-dependent evolution of spin-lattice interactions. Snapshots acquired from various simulations enable additional DFT investigations, providing a more sophisticated understanding of spin dynamics under temperature variations. By seamlessly integrating theoretical insights with computational approaches, the Density Functional Waltz emerges as a potent paradigm for unraveling the mesmerizing choreography of spin dynamics at the molecular scale. This review analyzes the evolution of machine-learning approaches in the field of chemical sciences. The proposed review will highlight the significance of collaboration between quantum catalysis and the chemical physics community. There is an outline of the unique features of electron spin alongside the ingenious integration of macromolecules to control and fine-tune electron spin-based innovation

Three-stage ultrafast demagnetization dynamics in a monolayer ferromagnet

Intense laser pulses can be used to demagnetize a magnetic material on an extremely short timescale. While this ultrafast demagnetization offers the potential for new magneto-optical devices, it poses challenges in capturing coupled spin-electron and spin-lattice dynamics. In this article, we study the photoinduced ultrafast demagnetization of a prototype monolayer ferromagnet Fe3GeTe2 and resolve the three-stage demagnetization process characterized by an ultrafast and substantial demagnetization on a timescale of 100 fs, followed by light-induced coherent A1g phonon dynamics which is strongly coupled to the spin dynamics in the next 200–800 fs. In the third stage, chiral lattice vibrations driven by nonlinear phonon couplings, both in-plane and out-of-plane are produced, resulting in significant spin precession. Nonadiabatic effects are found to introduce considerable phonon hardening and suppress the spin-lattice couplings during demagnetization. Our results advance our understanding of dynamic charge-spin-lattice couplings in the ultrafast demagnetization and evidence angular momentum transfer between the phonon and spin degrees of freedom.

Theory of tensorial Gilbert damping in antiferromagnets

Although the magnetic Gilbert damping was considered as a scalar quantity in micromagnetic and atomistic spin simulations, recent investigations show that the Gilbert damping parameter is a tensor. Here, we investigate the effect of anisotropic and chiral damping in one-sublattice ferromagnets and two-sublattice antiferromagnets. We employ linear response theory to calculate the susceptibility with the damping tensor and determine the ferromagnetic and antiferromagnetic resonance frequencies together with the effective damping. Our results show that apart from the scalar Gilbert damping, the antisymmetric chiral damping has a significant contribution to the spin dynamics that it breaks the antiparallel alignment of two sublattices in antiferromagnets even in the absence of an applied field. To this end, we also compare the tensorial damping and cross-sublattice scalar damping in antiferromagnets.

Layer-Number-Dependent Magnetism in the Co-Doped van der Waals Ferromagnet Fe3GaTe2.

Recently, van der Waals (vdW) antiferromagnets have been proposed to be crucial for spintronics due to their favorable properties compared to ferromagnets, including robustness against magnetic perturbation and high frequencies of spin dynamics. High-performance and energy-efficient spin functionalities often depend on the current-driven manipulation and detection of spin states, highlighting the significance of two-dimensional metallic antiferromagnets, which have not been much explored due to the lack of suitable materials. Here, we report a new metallic vdW antiferromagnet obtained from the ferromagnet Fe3GaTe2 by cobalt (Co) doping. Through the layer-number-dependent Hall resistance and magnetoresistance measurements, an evident odd-even layer-number effect has been observed in its few-layered flakes, suggesting that it could host an A-type antiferromagnetic structure. This peculiar layer-number-dependent magnetism in Co-doped Fe3GaTe2 helps unravel the complex magnetic structures in such doped vdW magnets, and our finding will enrich material candidates and spin functionalities for spintronic applications.

Noncentrosymmetric Triangular Magnet CaMnTeO6: Strong Quantum Fluctuations and Role of s0 versus s2 Electronic States in Competing Exchange Interactions.

Noncentrosymmetric triangular magnets offer a unique platform for realizing strong quantum fluctuations. However, designing these quantum materials remains an open challenge attributable to a knowledge gap in the tunability of competing exchange interactions at the atomic level. Here, a new noncentrosymmetric triangular S=3/2 magnet CaMnTeO6 is created based on careful chemical and physical considerations. The model material displays competing magnetic interactions and features nonlinear optical responses with the capability of generating coherent photons. The incommensurate magnetic ground state of CaMnTeO6 with an unusually large spin rotation angle of 127°(1) indicates that the anisotropic interlayer exchange is strong and competing with the isotropic interlayer Heisenberg interaction. The moment of 1.39(1)µB, extracted from low-temperature heat capacity and neutron diffraction measurements, is only 46% of the expected value of the static moment 3µB. This reduction indicates the presence of strong quantum fluctuations in the half-integer spin S=3/2 CaMnTeO6 magnet, which is rare. By comparing the spin-polarized band structure, chemical bonding, and physical properties of AMnTeO6 (A=Ca, Sr, Pb), how quantum-chemical interpretation can illuminate insights into the fundamentals of magnetic exchange interactions, providing a powerful tool for modulating spin dynamics with atomically precise control is demonstrated.

Multi-axis fields boost SABRE hyperpolarization

The inherently low signal-to-noise ratio of NMR and MRI is now being addressed by hyperpolarization methods. For example, iridium-based catalysts that reversibly bind both parahydrogen and ligands in solution can hyperpolarize protons (SABRE) or heteronuclei (X-SABRE) on a wide variety of ligands, using a complex interplay of spin dynamics and chemical exchange processes, with common signal enhancements between 103 and 104. This does not approach obvious theoretical limits, and further enhancement would be valuable in many applications (such as imaging mM concentration species in vivo). Most SABRE/X-SABRE implementations require far lower fields (μT-mT) than standard magnetic resonance (>1T), and this gives an additional degree of freedom: the ability to fully modulate fields in three dimensions. However, this has been underexplored because the standard simplifying theoretical assumptions in magnetic resonance need to be revisited. Here, we take a different approach, an evolutionary strategy algorithm for numerical optimization, multi-axis computer-aided heteronuclear transfer enhancement for SABRE (MACHETE-SABRE). We find nonintuitive but highly efficient multiaxial pulse sequences which experimentally can produce a sevenfold improvement in polarization over continuous excitation. This approach optimizes polarization differently than traditional methods, thus gaining extra efficiency.

Nonadiabatic Charge Transfer within Photoexcited Nickel Porphyrins.

Metalloporphyrins with open d-shell ions can drive biochemical energy cycles. However, their utilization in photoconversion is hampered by rapid deactivation. Mapping the relaxation pathways is essential for elaborating strategies that can favorably alter the charge dynamics through chemical design and photoexcitation conditions. Here, we combine transient optical absorption spectroscopy and transient X-ray emission spectroscopy with femtosecond resolution to probe directly the coupled electronic and spin dynamics within a photoexcited nickel porphyrin in solution. Measurements and calculations reveal that a state with charge-transfer character mediates the formation of the thermalized excited state, thereby advancing the description of the photocycle for this important representative molecule. More generally, establishing that intramolecular charge-transfer steps play a role in the photoinduced dynamics of metalloporphyrins with open d-shell sets a conceptual ground for their development as building blocks capable of boosting nonadiabatic photoconversion in functional architectures through "hot" charge transfer down to the attosecond time scale.

Magnetic Switching Dynamics and Tunnel Magnetoresistance Effect Based on Spin-Splitting Noncollinear Antiferromagnet Mn3Pt

In comparison to ferromagnets, antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices, including fast spin dynamics, vanishing stray fields and robust against external magnetic field, etc. However, unlike ferromagnetic orders, which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions, the antiferromagnetic order (i.e., Néel vector) cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets. Recently discovered spin-splitting noncollinear antiferromagnets, such as Mn3Pt with momentum-dependent spin polarization due to their special magnetic space group, make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions. Through first-principles calculations, we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn3Pt/perovskite oxides/Mn3Pt antiferromagnetic tunnel junctions. We also reveal the switching dynamics of Mn3Pt thin film under magnetic fields using atomistic spin dynamic simulation. Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.

Laser‐Induced Real‐Space Topology Control of Spin Wave Resonances

AbstractFemtosecond laser excitation of materials exhibiting magnetic spin textures promises advanced magnetic control via the generation of non‐equilibrium spin dynamics. Ferrimagnetic [Fe(0.35 nm)/Gd(0.40 nm)]160 multilayers are used to explore this approach, as they host a rich diversity of magnetic textures from stripe domains at low magnetic fields, a dense bubble/skyrmion lattice at intermediate fields, and a single domain state for high magnetic fields. Using femtosecond magneto‐optics, distinct coherent spin wave dynamics are observed in this material in response to a weak laser excitation, enabling an unambiguous identification of the different magnetic spin textures. Moreover, employing strong laser excitation, versatile control of the coherent spin dynamics via non‐equilibrium transformation of magnetic spin textures becomes possible by both creating and annihilating bubbles/skyrmions. Micromagnetic simulations and Lorentz transmission electron microscopy with in situ optical excitation corroborate these findings.

Polarization dynamics from moment equations

We derive an expression for the local transverse polarization of a boost-invariant expanding system of massive particles, which involves a set of dynamical spin moments. Starting from spin kinetic theory, we obtain a closed set of equations of motion for these spin moments. These equations are valid during the full evolution of the system, from free streaming to local equilibrium, and can be used to study polarization phenomena in relativistic heavy-ion collisions. Published by the American Physical Society 2024

Dynamics of the antiferromagnetic spin ice phase in pyrochlore spinels

Motivated by the classical spin-nematic state observed in the breathing pyrochlore spinel LiGa0.95In0.05Cr4O8, we theoretically discuss spin dynamics in models of spin-lattice coupling in these materials. Semiclassical dynamical simulations successfully recover the key features of inelastic neutron-scattering experiments on LiGa0.95In0.05Cr4O8: a broad finite-energy peak alongside a continuum of scattering near the (200) wave vector that extends from the elastic line to high energies. To interpret this result, we generalize linear-spin-wave theory for conventionally ordered magnets to the disordered spin-ice-like ground states expected for moderate spin-lattice coupling, which reproduces the numerical simulation results quantitatively. In particular, we find that the inelastic peak is well explained by collective modes confined to ferromagnetic loops of the underlying nematic order. In addition, we find a sharp, linearly dispersing mode in the dynamic structure factor, which originates in long-wavelength fluctuations of the nematic director. We believe identifying this mode will be an interesting target for future experiments on these materials. We also outline potential future applications of our methods to both pyrochlore spinels and other spin-nematic systems. Published by the American Physical Society 2024