Controlling Spin Dynamics Research Articles

Variation of Gilbert damping constant via interface induced magnetic anisotropy in LSMO/PMN-PT heterostructures

The field of spintronics is emerging at blistering pace due to its promising room-temperature applications in low-power logic-based devices. In this work, we investigate the suitability of ferromagnetic (FM) La0.7Sr0.3MnO3 (LSMO) thin film/ferroelectric (FE) Pb(Mg0.33Nb0.67)O3-PbTiO3 (PMN-PT) heterostructures for spintronic device applications through characterizing the static and dynamic magnetic properties. Due to the magnetoelastic coupling at the interface, LSMO/PMN-PT(001) is found to exhibit a 4-fold symmetry of magnetic anisotropy, while LSMO/PMN-PT(111) shows isotropic behavior at room temperature. The direction dependent Gilbert damping constant (α) estimated for the LSMO/PMN-PT(001) sample clearly shows that its values are smaller along the magnetically hard axis than along the easy axis, while no significant variation is observed for the LSMO/PMN-PT(111) sample. The electric field induced variation of α also demonstrate that the Gilbert damping is closely related to the magnetic anisotropy. The present results clearly indicate that it will be possible to realize electric field controlled spin dynamics in FM/FEs to develop futuristic spintronic devices.

Synthesis and photoinduced behavior of DPP-anchored nitronyl nitroxides: a multifaceted approach.

Understanding and controlling spin dynamics in organic dyes is of significant scientific and technological interest. The investigation of 2,5-dihydropyrrolo[4,3-c]pyrrolo-1,4-dione derivatives (DPPs), one of the most widely used dyes in many fields, has so far been limited to closed-shell molecules. We present a comprehensive joint experimental and computational study of DPP derivatives covalently linked to two nitronyl nitroxide radicals (DPPTh-NN2). Synthesis, single crystal X-ray diffraction study, photophysical properties, magnetic properties established using steady-state and pulse EPR, fast spin dynamics, and computational modelling using density functional theory and ab initio methods of electronic structure and spectroscopic properties of DPPTh-NN2 are presented. The single-crystal X-ray diffraction analysis of DPPTh-NN2 and computational modeling of its electronic structure suggest that effective conjugation along the backbone leads to noticeable spin-polarization transfer. Calculations using ab initio methods predict a weak exchange interaction of radical centers through a singlet ground state of DPPTh with a small singlet-triplet splitting (ΔEST) of about 25 cm-1 (∼0.07 kcal mol-1). In turn, a strong ferromagnetic exchange interaction between the triplet state of DPPTh chromophore and nitronyl nitroxides (with J ∼ 250 cm-1) was predicted.

Soliton solution for the integrable spin model with self-consistent potential

Integrable spin systems with potential are of great interest from the point of view of theoretical and applied physics. They make it possible to obtain accurate analytical solutions and study the properties of solitons - nonlinear wave structures that can be stable and move without distortion. The study of solitons in spin systems is of great importance not only for developing new methods for transmitting and processing information but also for developing spintronics and magnetoelectronics in general. These areas of technology are based on the use of the properties and control of the spin moment of electrons. Understanding and controlling spin dynamics in various systems opens up new possibilities for creating more efficient and powerful devices such as magnetic memories, spintronic transistors, and logic elements. This paper considers occurence of soliton in magnetic medium described by Generalized Landau-Lifshitz equation with self-consistent potential.

Mode splitting of spin waves in magnetic nanotubes with discrete symmetries

We investigate how geometry influences spin dynamics in polygonal magnetic nanotubes. We find that lowering the rotational symmetry of nanotubes by decreasing the number of planar facets, splits an increasing number of spin-wave modes, which are doubly degenerate in cylindrical tubes. This symmetry-governed splitting is distinct form the topological one recently observed in cylindrical nanotubes. Doublet modes with half-integer or integer multiple azimuthal periods of the number of facets, split to singlet pairs with lateral standing-wave profiles of opposing mirror-plane symmetries. Furthermore, the polygonal geometry facilitates the hybridization of modes with different azimuthal periods but the same symmetry, manifested in avoided level crossings. These phenomena, unimaginable in cylindrical geometry, provide new tools to control spin dynamics on nanoscale. The presented concept can be generalized to nano-objects of versatile geometries and order parameters, offering new routes to engineer dynamic response in nanoscale devices.

Unravelling Photoinduced Interlayer Spin Transfer Dynamics in Two-Dimensional Nonmagnetic-Ferromagnetic van der Waals Heterostructures.

Although light is the fastest means to manipulate the interfacial spin injection and magnetic proximity related quantum properties of two-dimensional (2D) magnetic van der Waals (vdW) heterostructures, its potential remains mostly untapped. Here, inspired by the recent discovery of 2D ferromagnets Fe3GeTe2 (FGT), we applied the real-time density functional theory (rt-TDDFT) to study photoinduced interlayer spin transfer dynamics in 2D nonmagnetic-ferromagnetic (NM-FM) vdW heterostructures, including graphene-FGT, silicene-FGT, germanene-FGT, antimonene-FGT and h-BN-FGT interfaces. We observed that laser pulses induce significant large spin injection from FGT to nonmagnetic (NM) layers within a few femtoseconds. In addition, we identified an interfacial atom-mediated spin transfer pathway in heterostructures in which the photoexcited spin of Fe first transfers to intralayered Te atoms and then hops to interlayered NM layers. Interlayer hopping is approximately two times slower than intralayer spin transfer. Our results provide the microscopic understanding for optically control interlayer spin dynamics in 2D magnetic heterostructures.

All-Dielectric Nanophotonics Enables Tunable Excitation of the Exchange Spin Waves.

Launching and controlling magnons with laser pulses opens up new routes for applications including optomagnetic switching and all-optical spin wave emission and enables new approaches for information processing with ultralow energy dissipation. However, subwavelength light localization within the magnetic structures leading to efficient magnon excitation that does not inherently absorb light has still been missing. Here, we propose to marriage the laser-induced ultrafast magnetism and nanophotonics to efficiently excite and control spin dynamics in magnetic dielectric structures. We demonstrate that nanopatterning by a 1D grating of trenches allows localization of light in spots with sizes of tens of nanometers and thus launch the exchange standing spin waves of different orders. The relative amplitude of the exchange and magnetostatic spin waves can be adjusted on demand by modifying laser pulse polarization, incidence angle, and wavelength. Nanostructuring of the magnetic media provides a unique possibility for the selective spin manipulation, a key issue for further progress of magnonics, spintronics, and quantum technologies.

Ultrafast optically induced spin transfer in ferromagnetic alloys.

The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism.

Laser Controlled Spin Dynamics of Ferromagnetic Thin Film from Femtosecond to Nanosecond Timescale

Permalloy (iron dissolved in nickel, in about a 1:4 ratio) is an important material for magnetic recording, due to its negligible magnetostriction and relatively low damping. This study of ultrafast magnetization dynamics investigates the correlation between phenomena occurring on time scales from femtoseconds to nanoseconds, following irradiation of a permalloy film by femtosecond laser pulses. The intrinsic Gilbert damping experiences a transient change with varying pump fluence, due to the rising ratio of system temperature to Curie temperature. The insight from this work is valuable for developing several varieties of magnetic data-storage technology.

Conjugated Oligomers with Stable Radical Substituents: Synthesis, Single Crystal Structures, Electronic Structure, and Excited State Dynamics

Understanding and controlling spin dynamics in organic semiconductors is of significant technological interest. We present a comprehensive joint experimental and computational study elucidating excited-state dynamics and kinetics of oligothiophenes covalently linked to two radicals. The synthesis, steady-state, and ultrafast photophysics, magnetic properties, computational modeling, and single crystal X-ray diffraction of a series of oligothiophenes with appended nitronyl nitroxide (NN) diradicals (RAx and RBx) are presented. We show that incorporation of the diradicals results in an intriguing molecular packing that is reminiscent of organic cages, unusual excited-state dynamics, and interesting photophysical and magnetic properties. We find an increase in the distance and dihedral angle between the diradical rings and the oligothiophene core result in weak antiferromagnetic interactions. Single crystal X-ray diffraction and computational modeling suggest that efficient conjugation along the backbone lea...

Alternative Directions to Control Spin Dynamics in Nuclear Magnetic Resonance and Physics

Alternative Directions to Control Spin Dynamics in Nuclear Magnetic Resonance and Physics

Efficient numerical integrator based on Fer expansion: Application to solid-state NMR experiments and to solve quantum Liouville equation and quantum Fokker-Planck equation

There are two important related research areas that I propose to investigate. First, we plan to develop an efficient numerical integrator based on Fer expansion for solid-state NMR simulation of experiments. Second, we intend to extend the method to solve quantum Liouville equation and quantum Fokker-Planck equation in order to improve the understanding of the dynamics of quantum systems subject to dissipation due to its relation to macroscopic quantum phenomena. The goal of the proposed research is to study a numerical integrator based on Fer expansion (Fer integrators of higher orders) in the integration of the time-dependent Schrodinger equation (TDSE) which is a central problem to nuclear magnetic resonance in general and solid-state NMR (SSNMR) in particular. The Fer integrator will provide to experts in quantum mechanics, NMR spectroscopy, and spin dynamics researchers, additional means for controlling spin dynamics in SSNMR. The efficient diagram will be used to compare the different orders of the Fer integrators obtained.

Voltage Control of Two-Magnon Scattering and Induced Anomalous Magnetoelectric Coupling in Ni-Zn Ferrite.

Controlling spin dynamics through modulation of spin interactions in a fast, compact, and energy-efficient way is compelling for its abundant physical phenomena and great application potential in next-generation voltage controllable spintronic devices. In this work, we report electric field manipulation of spin dynamics-the two-magnon scattering (TMS) effect in Ni0.5Zn0.5Fe2O4 (NZFO)/Pb(Mg2/3Nb1/3)-PbTiO3 (PMN-PT) multiferroic heterostructures, which breaks the bottleneck of magnetostatic interaction-based magnetoelectric (ME) coupling in multiferroics. An alternative approach allowing spin-wave damping to be controlled by external electric field accompanied by a significant enhancement of the ME effect has been demonstrated. A two-way modulation of the TMS effect with a large magnetic anisotropy change up to 688 Oe has been obtained, referring to a 24 times ME effect enhancement at the TMS critical angle at room temperature. Furthermore, the anisotropic spin-freezing behaviors of NZFO were first determined via identifying the spatial magnetic anisotropy fluctuations. A large spin-freezing temperature change of 160 K induced by the external electric field was precisely determined by electron spin resonance.

Reverse engineering protocols for controlling spin dynamics

We put forward reverse engineering protocols to shape in time the components of the magnetic field to manipulate a single spin, two independent spins with different gyromagnetic factors, and two interacting spins in short amount of times. We also use these techniques to setup protocols robust against the exact knowledge of the gyromagnetic factors for the one spin problem, or to generate entangled states for two or more spins coupled by dipole-dipole interactions.

ChemInform Abstract: Theoretical Approaches to Control Spin Dynamics in Solid‐State Nuclear Magnetic Resonance.

AbstractReview: 190 refs.

SPIDYAN, a MATLAB library for simulating pulse EPR experiments with arbitrary waveform excitation

Frequency-swept chirp pulses, created with arbitrary waveform generators (AWGs), can achieve inversion over a range of several hundreds of MHz. Such passage pulses provide defined flip angles and increase sensitivity. The fact that spectra are not excited at once, but single transitions are passed one after another, can cause new effects in established pulse EPR sequences. We developed a MATLAB library for simulation of pulse EPR, which is especially suited for modeling spin dynamics in ultra-wideband (UWB) EPR experiments, but can also be used for other experiments and NMR. At present the command line controlled SPin DYnamics ANalysis (SPIDYAN) package supports one-spin and two-spin systems with arbitrary spin quantum numbers. By providing the program with appropriate spin operators and Hamiltonian matrices any spin system is accessible, with limits set only by available memory and computation time. Any pulse sequence using rectangular and linearly or variable-rate frequency-swept chirp pulses, including phase cycling can be quickly created. To keep track of spin evolution the user can choose from a vast variety of detection operators, including transition selective operators. If relaxation effects can be neglected, the program solves the Liouville-von Neumann equation and propagates spin density matrices. In the other cases SPIDYAN uses the quantum mechanical master equation and Liouvillians for propagation. In order to consider the resonator response function, which on the scale of UWB excitation limits bandwidth, the program includes a simple RLC circuit model. Another subroutine can compute waveforms that, for a given resonator, maintain a constant critical adiabaticity factor over the excitation band. Computational efficiency is enhanced by precomputing propagator lookup tables for the whole set of AWG output levels. The features of the software library are discussed and demonstrated with spin-echo and population transfer simulations.

Theoretical approaches to control spin dynamics in solid-state nuclear magnetic resonance

This article reviews theoretical approaches for controlling spin dynamics in solid-state nuclear magnetic resonance. We present fundamental theories in the history of NMR, namely, the average Hamiltonian and Floquet theories. We also discuss emerging theories such as the Fer and Floquet-Magnus expansions. These theories allow one to solve the time-dependent Schrodinger equation, which is still the central problem in spin dynamics of solid-state NMR. Examples from the literature that highlight several applications of these theories are presented, and particular attention is paid to numerical integrators and propagator operators. The problem of time propagation calculated with Chebychev expansion and the future development of numerical directions with the Cayley transformation are considered. The bibliography includes 190 references.

Time to get the nukes out

The ability to electrically control spin dynamics in quantum dots makes them one of the most promising platforms for solid-state quantum-information processing. Minimizing the influence of the nuclear spin environment is an important step towards realizing such promise.

Spin dynamics in (1 1 0)-oriented quantum wells

Quantum structures of III–V semiconductors grown on (110)-oriented substrates are promising for spintronic applications because they allow us to engineer and control spin dynamics of electrons. We summarise the theoretical ideas, which are the basis for this claim and review experiments to investigate them.