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Polyoxometalates (POMs) are nanosized molecular metal oxide anion clusters with tuneable structures and functionalities, and they exhibit a redox chemistry and catalytic activity in multielectron redox processes. These are typically poor electrical conductors (<10−10 Scm−1), which is attributed to negligible electronic interactions among anions in the solid state. Since the reduced electrons on the d0 metals in POMs are delocalized, electrical conductivity was improved when judicious pathways for the electrons were created by bridging the POMs. Utilized with the electronic interactions between bridging oxygen atoms with the highest occupied molecular orbital in the POMs and the metal dz2 orbitals in the multinuclear platinum complexes, and three mixed‐valent assemblies were synthesized and characterized. Simply mixing Keggin‐type or Dawson‐type POMs with tetranuclear or trinuclear platinum complexes in solution afforded three single crystals, and all three compounds were paramagnetic with mixed oxidation states and better conductivities at room temperature than the parent compounds. [ABSTRACT FROM AUTHOR]

The magnetic properties of Ni nanoparticles (NPs) with diameter D are investigated using spin-lattice dynamics (SLD) simulations. Using exchange interactions fitted to ab-initio results we obtain a Curie temperature, T c , similar, but lower, than experiments. In order to reproduce quantitatively the bulk Curie temperature and the experimental results, the exchange energy has to be increased by 25% compared to the ab-initio value. During the simulated time, Ni NPs remain ferromagnetic down to the smallest sizes investigated here, containing around 500 atoms. The average magnetic moment of the NPs is slightly smaller than that determined experimentally. By considering a core-shell model for NPs, in which the shell atoms are assigned a larger magnetic moment, this discrepancy can be removed. T c is lower for a moving lattice than for a frozen lattice, as expected, but this difference decreases with NP size because smaller NPs include higher surface disorder which dominates the transition. For NPs, T c decreases with the NP diameter D by at most 10% at D = 2 nm, in agreement with several experiments, and unlike some modeling or theoretical scaling results which predict a considerably larger decrease. The decrease of T c is well described by finite-size scaling models, with a critical exponent that depends on the SLD settings for a frozen or moving lattice, and also depends on the procedure for determining T c . Extrapolating the inverse of the magnetization as function of temperature near T c gives a lower T c than the maximum of the susceptibility. [ABSTRACT FROM AUTHOR]

In the quest for 2D conducting materials with high ferromagnetic ordering temperature the new family of the layered FenGeTe2 compounds, especially the near‐room‐temperature ferromagnet Fe4GeTe2, receives a significant attention. Fe4GeTe2 features a peculiar spin reorientation transition at TSR ≈ 110 K suggesting a non‐trivial temperature evolution of the magnetic anisotropy (MA)—one of the main contributors to the stabilization of the magnetic order in the low‐dimensional systems. An electron spin resonance (ESR) spectroscopic study reported here provides quantitative insights into the unusual magnetic anisotropy of Fe4GeTe2. At high temperatures the total MA is mostly given by the demagnetization effect with a small contribution of the counteracting intrinsic magnetic anisotropy of an easy‐axis type, whose growth below a characteristic temperature Tshape ≈ 150 K renders the sample seemingly isotropic at TSR. Below one further temperature Td ≈ 50 K the intrinsic MA becomes even more complex. Importantly, all the characteristic temperatures found in the ESR experiment match those observed in transport measurements, suggesting an inherent coupling between magnetic and electronic degrees of freedom in Fe4GeTe2. This finding together with the observed signatures of the intrinsic two‐dimensionality should facilitate optimization routes for the use of Fe4GeTe2 in the magneto‐electronic devices, potentially even in the monolayer limit. [ABSTRACT FROM AUTHOR]

In the quest for 2D conducting materials with high ferromagnetic ordering temperature the new family of the layered FenGeTe2 compounds, especially the near‐room‐temperature ferromagnet Fe4GeTe2, receives a significant attention. Fe4GeTe2 features a peculiar spin reorientation transition at TSR ≈ 110 K suggesting a non‐trivial temperature evolution of the magnetic anisotropy (MA)—one of the main contributors to the stabilization of the magnetic order in the low‐dimensional systems. An electron spin resonance (ESR) spectroscopic study reported here provides quantitative insights into the unusual magnetic anisotropy of Fe4GeTe2. At high temperatures the total MA is mostly given by the demagnetization effect with a small contribution of the counteracting intrinsic magnetic anisotropy of an easy‐axis type, whose growth below a characteristic temperature Tshape ≈ 150 K renders the sample seemingly isotropic at TSR. Below one further temperature Td ≈ 50 K the intrinsic MA becomes even more complex. Importantly, all the characteristic temperatures found in the ESR experiment match those observed in transport measurements, suggesting an inherent coupling between magnetic and electronic degrees of freedom in Fe4GeTe2. This finding together with the observed signatures of the intrinsic two‐dimensionality should facilitate optimization routes for the use of Fe4GeTe2 in the magneto‐electronic devices, potentially even in the monolayer limit. [ABSTRACT FROM AUTHOR]

This study demonstrates effective manipulation of exciton spin dynamics in a prototypical chiral inorganic nanosystem, i.e., cadmium selenide (CdSe) nanosheets capped with chiral cysteine ligands in aqueous solution, via facile pH‐regulation that can directly modify the electronic coupling between CdSe and cysteine's thiol group through Cd─S bonding. The comparative scrutiny by using transient circular dichroism spectroscopy enables to decipher the pertinent mechanisms behind the pH‐regulated spin‐flip dynamics. The hole‐trapping interaction between the valence‐band heavy‐hole spin state of CdSe and the cysteine‐induced "extrinsic" surface state is found to play a dominant role in prolonging the hole spin relaxation lifetime (by more than threefold). This study also demonstrates a relevant application in modulating the sensitivity of circularly polarized light detection. This work sets a paradigm for harnessing the elusive interactions in chiral inorganic nanosystems to achieve desired spin‐polarization regulation, refreshing the fundamental understanding about the mechanisms of spin dynamics involved therein. [ABSTRACT FROM AUTHOR]

Abstract The magnetic properties of Ni nanoparticles (NPs) with diameter D are investigated using spin-lattice dynamics (SLD) simulations. Using exchange interactions fitted to ab-initio results we obtain a Curie temperature, $$T_c$$ T c , similar, but lower, than experiments. In order to reproduce quantitatively the bulk Curie temperature and the experimental results, the exchange energy has to be increased by 25% compared to the ab-initio value. During the simulated time, Ni NPs remain ferromagnetic down to the smallest sizes investigated here, containing around 500 atoms. The average magnetic moment of the NPs is slightly smaller than that determined experimentally. By considering a core-shell model for NPs, in which the shell atoms are assigned a larger magnetic moment, this discrepancy can be removed. $$T_c$$ T c is lower for a moving lattice than for a frozen lattice, as expected, but this difference decreases with NP size because smaller NPs include higher surface disorder which dominates the transition. For NPs, $$T_c$$ T c decreases with the NP diameter D by at most 10% at $$D=2$$ D = 2 nm, in agreement with several experiments, and unlike some modeling or theoretical scaling results which predict a considerably larger decrease. The decrease of $$T_c$$ T c is well described by finite-size scaling models, with a critical exponent that depends on the SLD settings for a frozen or moving lattice, and also depends on the procedure for determining $$T_c$$ T c . Extrapolating the inverse of the magnetization as function of temperature near $$T_c$$ T c gives a lower $$T_c$$ T c than the maximum of the susceptibility.

An insulator‐based spin‐thermoelectric (STE) generator is composed of a thin paramagnetic metal (PM: Pt) layer for generating the STE voltage VSTE via the inverse spin Hall effect and a ferrimagnetic insulator (FMI) film or slab used for producing spin‐wave spin currents due to a temperature gradient ∇T$$ \nabla T $$. Yttrium iron garnet (YIG) is a key material used for the FMI of STE generators. We examined in detail the ferromagnetic resonance (FMR) properties of YIG (Y3Fe5O12), Bi‐substituted YIG (Y3‐xBixFe5O12) and Bi‐ and Al‐substituted YIG (Y3‐xBixFe5‐yAlyO12) films grown by liquid phase epitaxy (LPE). Bi‐substituted YIG films exhibited the large FMR damping and high STE voltage when the films were incorporated in the STE generator. The LPE‐grown Y2.35Bi0.65Fe5O12 film exhibited the FMR linewidth ΔH of 30 mT and the VSTE of 70 μV for the ∇T of 90×10−3°C/μm$$ 90\times {10}^{-3{}^{\circ}}C/\upmu \mathrm{m} $$. This paper comprehensively presents the origin of the STE generation in the insulator‐based generators on the basis of the results of FMR and STE measurements. To clarify the origin of STE generation in the generators fabricated from single crystal YIG (YIG, Bi‐substituted YIG and Bi‐ and Al‐substituted YIG) films grown by LPE, three principal factors are explained: (a) thermal energy transfer from the phonon system to the spin system, which strengthens the heat excitation of spin precession, through the spin–orbit coupling enhanced by the growth‐induced magnetic anisotropy of LPE‐grown YIG films, (b) in the YIG films incorporated in the STE generators, the generation of spin‐wave spin currents owing its origin to the ferromagnetic spin exchange interaction acting between neighboring spins due to ∇T$$ \nabla T $$, and (c) how the spin currents pumped into the Pt layer from the YIG film at the Pt/YIG bilayer interface are affected by the magnetization processes of single crystal YIG films. It is concluded that the STE generation of insulator‐based STE generators can be explained from a viewpoint of the spin dynamics under the effect of ∇T$$ \nabla T $$ in the Pt/YIG bilayer structure. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

2D magnetic materials hold substantial promise in information storage and neuromorphic device applications. However, achieving a 2D material with high Curie temperature (TC), environmental stability, and multi‐level magnetic states remains a challenge. This is particularly relevant for spintronic devices, which require multi‐level resistance states to enhance memory density and fulfil low power consumption and multi‐functionality. Here, the synthesis of 2D non‐layered triangular and hexagonal magnetite (Fe3O4) nanosheets are proposed with high TC and environmental stability, and demonstrate that the ultrathin triangular nanosheets show broad antiphase boundaries (bAPBs) and sharp antiphase boundaries (sAPBs), which induce multiple spin precession modes and multi‐level resistance. Conversely, the hexagonal nanosheets display slip bands with sAPBs associated with pinning effects, resulting in magnetic‐field‐driven spin texture reversal reminiscent of "0" and "1" switching signals. In support of the micromagnetic simulation, direct explanation is offer to the variation in multi‐level resistance under a microwave field, which is ascribed to the multi‐spin texture magnetization structure and the randomly distributed APBs within the material. These novel 2D magnetite nanosheets with unique spin textures and spin dynamics provide an exciting platform for constructing real multi‐level storage devices catering to emerging information storage and neuromorphic computing requirements. [ABSTRACT FROM AUTHOR]

The spin degree of freedom in hybrid organic–inorganic perovskites (HOIPs) has become a rapidly growing research topic in both HOIPs and spintronics fields due to its fundamental scientific significance and tight relevance with optoelectronics. The flourishing achievements of HOIP spintronics call for a timely review to summarize the key progress and guide future developments. In this review, classical spintronic phenomena based on spin‐orbit coupling (SOC) are discussed, especially Rashba splitting and related applications such as spin‐charge conversion. Owing to the unique chirality‐spin coupling, spintronics in chiral HOIPs are particularly focused on, including chirality‐induced spin selectivity (CISS). Based on the complex band structure and carrier/exciton, spin dynamics is also widely investigated and constitutes an indispensable part of HOIP spintronics. Aside from the three main threads, other spintronic phenomena such as magneto‐optical coupling and device exploration are involved as promising opportunities. Despite the continuous breakthroughs in HOIP spintronics, more efforts are required to expand material systems, explore new physics, and optimize device configurations for enhanced performance and high integration. A deep understanding of spin behaviors in HOIPs will create a new platform beyond conventional optoelectronic and photovoltaic applications. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the spin–orbit coupling of F = 1 dipolar Bose–Einstein condensates in a quasi-one-dimensional trap by solving the mean field Gross–Pitaevskii equation. We focus on the two phases, ferromagnetic and antiferromagnetic. For the former, we find that the spin echo signal emerges gradually as the spin–orbit coupling strength increases, which favors miscibility in density profile. The dipolar interaction plays a tiny role in the spin dynamics process, the qualitative behavior remains almost unchanged. Nevertheless, for the antiferromagnetic phase, the physical picture greatly changes. The spin echo signal abruptly increases with the increase in spin–orbit coupling strength, and the density structure exhibits phase separation. With the emergence of dipolar interaction, the spin echo signal vanishes, and the evolution of the three components is ruleless. Meanwhile, the condensate deviates from the property of phase separation. Also, we analyze the effect of the number of atoms on spin dynamics. It is obvious that the reduction of atoms increases the number of spin echo signals for the ferromagnetic phase regardless of the nature of dipolar interaction. In addition, for the antiferromagnetic phase, such a decrease gives rise to the disappearance of the spin echo signal in the absence of dipolar interaction, and its influence is small when dipolar interaction is added. [ABSTRACT FROM AUTHOR]

In this paper, we study the dynamic properties of spin–orbit coupling (SOC) hyperfine f =1 spinor antiferromagnetic Bose–Einstein condensates with the external magnetic field. The condensate is confined in a toroidal trap and the numerical results are obtained based on the multicomponent Gross–Pitaevskii equation. Our results show that, in the presence of SOC, the spin dynamics for zero magnetic field slows with an increase of radius of the torus. However, this process accelerates when the magnetic field is considered. In addition, in this case, the oscillation behavior is almost consistent with the considered maximum radius. In the absence of SOC, the periodicity of spin dynamics vanishes. We also compare the thermalization time for different magnetic fields and radii, which decreases considerably for nonzero magnetic fields with the increase of radius. Furthermore, our analysis suggests that for stronger magnetic field strength the density structure can be regulated. As a consequence, the condensate recovers from the necklace to an annular-shaped state. [ABSTRACT FROM AUTHOR]

Understanding the origin and mechanisms of magnetic damping in complex oxide materials is crucial for optimizing spin dynamics and tailoring their properties for specific spintronic applications. Ferromagnetic resonance spectroscopy (FMR) technique has been used to investigate the magnetic damping of multiple La2/3Sr1/3MnO3 (LSMO) epitaxial thin films with similar thickness and identical DC magnetic properties. However, the dynamic magnetic properties exhibit noticeable variations among samples. Microstructural analyses using X-ray diffraction (XRD) and atomic force microscopy (AFM), confirm that the samples are structurally identical, except for minute differences in the miscut angles of the substrates. Nevertheless, when examining the samples using backscattered electron (BSE) images in scanning electron microscopy (SEM), significant disparities in the twin distribution are observed. These variations in the twin distribution directly correlate with the observed differences in the damping values. A careful image analysis of BSE images allows to demonstrate that the increase of damping is due to the pinning of the magnetization in the twin boundaries. [ABSTRACT FROM AUTHOR]

Quantum sensing is a quantum technology for ultrasensitive detection, which is particularly useful for sensing weak signals at the nanoscale. Nitrogen vacancy centers in diamond, thanks to their superb quantum coherence under ambient conditions and the stability of the material in extreme and complicated environments, have been demonstrated as promising quantum probes in multi-parameter sensing. Their spin properties make them particularly sensitive to magnetic fields, but they are insensitive to temperature, electric field, pressure, etc., and even immune to some bio-parameters (e.g., pH and glucose concentration). Recently, hybrid quantum sensing has emerged as a promising avenue for further enhancing the capabilities of diamond sensors. Different techniques can potentially improve the sensitivity, range of detectable parameters, and sensing frequencies of diamond sensors. This review provides an overview of hybrid quantum sensing using diamond. We first give a brief introduction to quantum sensing using diamond, and then review various hybrid sensing schemes that have been developed to enhance the sensing capabilities of diamond sensors. Finally, the potential applications and challenges associated with hybrid quantum sensing in diamond are discussed. [ABSTRACT FROM AUTHOR]

Understanding magnetotransport properties in semiconductors plays a vital role in either developing future spintronic or unveiling the underpinning physics of electronic dynamics. In recent years, the high‐field magnetoconductance (HFM, B ~ 1 T) in polymers has drawn intense discussions and always been attributed to thermal spin polarization (TSP). In this work, the HFMs in several benchmark polymers are proposed to be correlated to the ∆g spin‐mixing effect, determined from their remarkable anisotropy in response to magnetic fields, which cannot be explained only by TSP. It is the fundamental difference between two spins' Lande factors stemming from the random orientations of molecular backbones that contributes to the intense ∆g spin‐mixing effect, leading to HFMs' anisotropy as high as 150%. It is further found that the ∆g spin‐mixing mechanism greatly correlates with the charge transport dynamics in polymers, in which a slow‐ to fast‐hopping crossover was observed and further verified by pressure‐dependent HFMs characteristics. [ABSTRACT FROM AUTHOR]

Abstract 2D magnetic materials hold substantial promise in information storage and neuromorphic device applications. However, achieving a 2D material with high Curie temperature (TC), environmental stability, and multi‐level magnetic states remains a challenge. This is particularly relevant for spintronic devices, which require multi‐level resistance states to enhance memory density and fulfil low power consumption and multi‐functionality. Here, the synthesis of 2D non‐layered triangular and hexagonal magnetite (Fe3O4) nanosheets are proposed with high TC and environmental stability, and demonstrate that the ultrathin triangular nanosheets show broad antiphase boundaries (bAPBs) and sharp antiphase boundaries (sAPBs), which induce multiple spin precession modes and multi‐level resistance. Conversely, the hexagonal nanosheets display slip bands with sAPBs associated with pinning effects, resulting in magnetic‐field‐driven spin texture reversal reminiscent of “0” and “1” switching signals. In support of the micromagnetic simulation, direct explanation is offer to the variation in multi‐level resistance under a microwave field, which is ascribed to the multi‐spin texture magnetization structure and the randomly distributed APBs within the material. These novel 2D magnetite nanosheets with unique spin textures and spin dynamics provide an exciting platform for constructing real multi‐level storage devices catering to emerging information storage and neuromorphic computing requirements.

We derive a quantum Langevin equation for a quantum spin in the presence of a magnetic field and coupled to a bath. We have considered two models for the bath: an Ohmic bath model and a non-Markovian Drude bath model with finite memory. The effect of finite memory on the dynamics of the quantum spin is studied in detail. In particular, we have studied the effect of memory on the expectation values of the magnetic moment and the spin correlation functions. The time evolution study of the spin correlation functions shows that the correlation functions exhibit a damped oscillatory behavior with the randomization time being determined by the damping rate. We have analytically shown that the damping gets affected by the finite memory time when the bath retains memory of the interaction with the system. We also analyze the spin response function of the system for the Ohmic bath. Our results qualitatively agree with the findings in spin noise spectroscopy experiments and our predictions can be tested in future ultracold atom experiments. [ABSTRACT FROM AUTHOR]

Quantum objects, such as atoms, spins, and subatomic particles, haveunique physical properties that could be useful for many different applications, ranging from quantum information processing to magnetic resonance imaging. Molecular species also exhibit these quantum properties, and, importantly, these properties are fundamentally tunable by synthetic design, unlike ions isolated in a quadrupolar trap, for example. In this comment, we distill multiple, distinct, scientific efforts into an emergent field that is devoted to designing molecules that mimic the quantum properties of objects like trapped atoms or defects in solids. Mimicry is endemic in inorganic chemistry and featured heavily in the research interests of groups across the world. We describe this new field of using molecular inorganic chemistry to mimic the quantum properties (e.g. the lifetime of spin superpositions, or the resonant frequencies thereof) of other quantum objects as "quantum mimicry." In this comment, we describe the philosophical design strategies and recent exciting results from the application of these strategies. [ABSTRACT FROM AUTHOR]

Low-dimensional perovskite (PVK) materials have attracted significant research interest, because of their quantum-confined effect, tunable band gap structures, and higher stability than that of three-dimensional (3D) PVKs. In semiconductor optoelectronic devices, high speed and small size are closely interlinked. The development of high-speed devices requires researchers to fully understand the properties of materials, especially the dynamic processes such as carrier recombination, separation, and transport, which often play a crucial role in the performance of devices. As an indispensable part of dynamic research, spin relaxation is also of great significance in studying the properties of materials and explore possible applications. Lead halide PVK materials have strong spin-orbit coupling (SOC), which provides a basis for information storage and processing by using spin degrees of freedom. Therefore, studying the carrier and spin dynamics of low-dimensional PVKs is an effective way to understand the internal properties of low-dimensional PVKs clearly. This paper summarizes the latest research progress on the ultrafast carrier and spin dynamics in low-dimensional PVKs, to comprehensively understand their carrier and spin behaviors and present an outlook for relevant studies in this area. [ABSTRACT FROM AUTHOR]

Ferromagnetic materials have important exploitation practice in permanent information in electromagnets, electric motors, generators, recording in thin film etc. This research explores spin dynamic soliton in Ferromagnetic materials via the (2 + 1)-D Heisenberg ferro-magnetic Spin Chains (HFSC) model. The Extended (I,R) and Extended Simple schemes treatment are applied to integrate the model. Through the technique, various novel dynamical wave solutions afford as optical dark and bright soliton envelope, spin wave envelope Black soliton, optical bell-shock interaction, optical bell-anti-shock wave, optical Dark-bright bell soliton and optical bright periodic waves from modulus plots, besides these real and imaginary profiles exhibits bright periodic wave with dark bell wave, periodically increasing–decreasing carrier wave, periodic carrier wave increase its amplitude by shock, periodic carrier wave suddenly decrease its amplitude by shock waves. The effect of fractional derivative, neighboring interaction as well as uniaxial crystal field anisotropy parameters is explored on the envelope soliton and amplitude of carrier waves. The changing value of neighboring interaction parameters are exhibited as increases wave height with the increases of parametric values, but while increasing values of the uni-axial crystal arena anisotropy factor causes the reduction of wave heights.

Quantum sensing is a quantum technology for ultrasensitive detection, which is particularly useful for sensing weak signals at the nanoscale. Nitrogen vacancy centers in diamond, thanks to their superb quantum coherence under ambient conditions and the stability of the material in extreme and complicated environments, have been demonstrated as promising quantum probes in multi-parameter sensing. Their spin properties make them particularly sensitive to magnetic fields, but they are insensitive to temperature, electric field, pressure, etc., and even immune to some bio-parameters (e.g., pH and glucose concentration). Recently, hybrid quantum sensing has emerged as a promising avenue for further enhancing the capabilities of diamond sensors. Different techniques can potentially improve the sensitivity, range of detectable parameters, and sensing frequencies of diamond sensors. This review provides an overview of hybrid quantum sensing using diamond. We first give a brief introduction to quantum sensing using diamond, and then review various hybrid sensing schemes that have been developed to enhance the sensing capabilities of diamond sensors. Finally, the potential applications and challenges associated with hybrid quantum sensing in diamond are discussed.

This article provides a brief overview of advanced magnetic X-ray spectro-microscopies that are widely used in characterizing mesoscopic magnetic materials. Common to those techniques are various X-ray magnetic dichroism effects that are used as magnetic contrast mechanism. A particular interest is to use those techniques to image the underlying microscopic spin structures in magnetic materials with high spatial resolution and to ultimately resolve their full 3D mesoscale characteristics with elemental sensitivity, as well as their ultrafast dynamics upon excitations with field and current pulses. Recent research examples using various magnetic X-ray spectro-microscopies are presented to showcase their specific features with a focus on imaging novel topological spin textures, such as vortices, skyrmions and Hopfions, which are considered as potential building blocks towards low power, high-speed and high-density magnetic devices that could transform information technologies and potentially be used in biomedical applications. Future developments with magnetic X-ray spectro-microscopies harness the full coherence of next generation X-ray sources and could open the path towards single shot imaging with spatial and temporal resolutions down to fundamental magnetic length and time scales.

Spin relaxation is an important aspect of the spin dynamics of free radicals and can have a significant impact on the outcome of their spin‐selective reactions. Examples range from the use of radicals as spin qubits in quantum information processing to the radical pair reactions in proteins that may allow migratory birds to sense the direction of the Earth's magnetic field. Accurate modeling of spin relaxation, however, is non‐trivial. Bloch–Redfield–Wangsness theory derives a quantum mechanical master equation from system‐bath interactions in the Markovian limit that provides a comprehensive framework for describing spin relaxation. Unfortunately, the construction of the master equation is system‐specific and often resource‐heavy. To address this challenge, we introduce a generalized and efficient implementation of BRW theory as a new feature of the spin dynamics toolkit MolSpin which offers an easy‐to‐use approach for studying systems of reacting radicals of varying complexity. [ABSTRACT FROM AUTHOR]

The coexistence of two spin components with different Larmor frequencies in colloidal CdSe and CdS quantum dots (QDs) leads to the entanglement of spin signals, complicating the analysis of dynamic processes and hampering practical applications. Here, we explored several methods, including varying the types of hole acceptors, air or anaerobic atmosphere and laser repetition rates, in order to facilitate the obtention of one single Larmor frequency in the coherent spin dynamics using time-resolved ellipticity spectroscopy at room temperature. In an air or nitrogen atmosphere, manipulating the photocharging processes by applying different types of hole acceptors, e.g., Li[Et3BH] and 1-octanethiol (OT), can lead to pure spin components with one single Larmor frequency. For as-grown QDs, low laser repetition rates favor the generation of the higher Larmor frequency spin component individually, while the lower Larmor frequency spin component can be enhanced by increasing the laser repetition rates. We hope that the explored methods can inspire further investigations of spin dynamics and related photophysical processes in colloidal nanostructures. [ABSTRACT FROM AUTHOR]

An important vision of modern magnetic research is to use antiferromagnets (AFMs) as controllable and active ultrafast components in spintronic devices. Hematite (α‐Fe2O3) is a promising model material in this respect because its pronounced Dzyaloshinskii‐Moriya interaction leads to the coexistence of antiferromagnetism and weak ferromagnetism. Here, femtosecond laser pulses are used to drive terahertz (THz) spin currents from α‐Fe2O3 into an adjacent Pt layer. Two contributions to the generation of the spin current with distinctly different dynamics are found: the impulsive stimulated Raman scatting that relies on the AFM order and the ultrafast spin Seebeck effect that relies on the net magnetization. The total THz spin current dynamics can be manipulated by a medium‐strength magnetic field below 1 T. The control of the THz spin current achieved in α‐Fe2O3 opens the pathway toward tailoring the exact spin current dynamics from ultrafast AFM spin sources. [ABSTRACT FROM AUTHOR]

Based on magneto‐electric (ME) effect and spin Hall effect (SHE), the authors propose a novel spin logic device named MESH‐SLD. In MESH‐SLD, the charge current is transmitted in the channel by employing inverse SHE, which solves the dissipation problem of spin current in the channel of all‐spin logic device (ASLD). By using a magnetization‐dynamics/spin‐transport hybrid model, the authors have investigated the influence of working voltage, channel lengths, and materials on the performance of the MESH‐SLD. And the simulation results show that the energy dissipation of the MESH‐SLD only increases approximately linearly with the increase of channel length, while the switching delay remains almost unchanged. In addition, with the increase of the spin Hall angle of the channel material, the energy dissipation and the minimum working voltage of the MESH‐SLD decrease significantly. Most importantly, compared with conventional ASLD, the proposed MESH‐SLD improve the switching delay and the energy dissipation by about 2.5 times and 851.8 times, respectively. [ABSTRACT FROM AUTHOR]

Abstract Ensembles of negatively charged nitrogen-vacancy centers (NV−) in diamond have been proposed for sensing of magnetic fields and paramagnetic agents, and as a source of spin-order for the hyperpolarization of nuclei in magnetic resonance applications. To this end, strongly fluorescent nanodiamonds (NDs) represent promising materials, with large surface areas and dense ensembles of NV−. However, surface effects tend to favor the less useful neutral form, the NV0 centers, and strategies to increase the density of shallow NV− centers have been proposed, including irradiation with strong laser power (Gorrini in ACS Appl Mater Interfaces. 13:43221–43232, 2021). Here, we study the fluorescence properties and optically detected magnetic resonance (ODMR) of NV− centers as a function of laser power in strongly fluorescent bulk diamond and in nanodiamonds obtained by nanomilling of the native material. In bulk diamond, we find that increasing laser power increases ODMR contrast, consistent with a power-dependent increase in spin-polarization. Conversely, in nanodiamonds we observe a non-monotonic behavior, with a decrease in ODMR contrast at higher laser power. We hypothesize that this phenomenon may be ascribed to more efficient NV−→NV0 photoconversion in nanodiamonds compared to bulk diamond, resulting in depletion of the NV− pool. A similar behavior is shown for NDs internalized in macrophage cells under the typical experimental conditions of imaging bioassays. Our results suggest strong laser irradiation is not an effective strategy in NDs, where the interplay between surface effects and local microenvironment determine the optimal experimental conditions.

Cross polarization (CP) is a widely used solid-state nuclear magnetic resonance (NMR) technique for enhancing the polarization of dilute S spins from much larger polarization of abundant I spins such as 1H. To achieve such a polarization transfer, the I spin should either be spin-locked or be converted to the dipolar ordered state through adiabatic demagnetization in the rotating frame. In this work, we analyze the spin dynamics of the Hartmann-Hahn CP (HHCP) utilizing the 1H spin-locking, and the dipolar-order CP (DOCP) having the 1H adiabatic demagnetization. We further propose an adiabatic demagnetization CP (ADCP) where a constant radio-frequency pulse is applied on the S spin while 1H is adiabatically demagnetized. Our analyses indicate that ADCP utilizes the adiabatic passage to effectively achieve the polarization transfer from the 1H to S spins. In addition, the dipolar ordered state generated during the 1H demagnetization process could also be converted into the observable S polarization through DOCP, further enhancing the polarized signals. It is shown by both static and magic-angle-spinning (MAS) NMR experiments that ADCP has dramatically broadened the CP matching condition over the other CP schemes. Various samples have been used to demonstrate the polarization transfer efficiency of this newly proposed ADCP scheme.

Fast spin manipulation in magnetic heterostructures, where magnetic interactions between different materials often define the functionality of devices, is a key issue in the development of ultrafast spintronics. Although recently developed optical approaches such as ultrafast spin‐transfer and spin–orbit torques open new pathways to fast spin manipulation, these processes do not fully utilize the unique possibilities offered by interfacial magnetic coupling effects in ferromagnetic multilayer systems. Here, ultrafast optically controlled interfacial exchange interactions in the ferromagnetic Co2FeAl/(Ga,Mn)As system at low laser fluence levels are experimentally demonstrated. The excitation efficiency of Co2FeAl with the (Ga,Mn)As layer is 30–40 times higher than the case with the GaAs layer at 5 K due to the modification of exchange coupling interaction via photoexcited charge transfer between the two ferromagnetic layers. In addition, the coherent spin precessions persist to room temperature, excluding the drive of pump‐modulated magnetization in the (Ga,Mn)As layer and indicating a proximity‐effect‐related optical excitation mechanism. The results highlight the importance of interfacial exchange interactions in ferromagnetic heterostructures and how these magnetic coupling effects can be utilized for ultrafast, low‐power spin manipulation. [ABSTRACT FROM AUTHOR]

In this paper, we study the dynamics properties of three-component antiferromagnetic dipolar Bose–Einstein condensates with external magnetic field. Our results are obtained by numerical simulations of the spinor Gross–Pitaevskii equation. We find that the population of the spin components is seriously influenced by magnetic field. The dynamical evolution process is accelerated in the presence of magnetic field. As a result, the periodic oscillation of spin exchange dynamics emerges and the components m f = ± 1 have the same amplitude. In addition, the density profile displays that the influences of dipolar interaction are masked by magnetic field. Moreover, we introduce an order parameter to characterize the disorder-order crossover, where it is seen that the system develops toward the disordered state with strong dipole strength when magnetic field is included. [ABSTRACT FROM AUTHOR]

Cyclic 3d-4f molecular magnets have received considerable attention owing to their potential applications in high-density data storage and quantum information processing. As a rare example of ferromagnetic polynuclear Cr rings, {Cr8Y8} represents a valuable test bed to directly study the magnetic interaction between Cr3+ ions in large hexadecametallic {Cr8Ln8} (Ln = 4f metal) molecules. We have proposed a "single-J" model to approximate the low-temperature spin dynamics of {Cr8Y8} in our earlier study, while a zero-field splitting (ZFS) of the quantum levels was also suggested by the heat capacity data. In order to have a deeper understanding of the magnetism of {Cr8Y8}, it is necessary to verify the ZFS by means of high-resolution spectral methods and identify its origin. In this work, we present a high-frequency electron spin resonance (HF-ESR) study on the ZFS of {Cr8Y8}. The X-band ESR spectra consists of multi-peak structure, indicative of magnetic anisotropy that breaks the degeneracy between spin states in the absence of a magnetic field. HF-ESR spectra are collected to extract the ZFS parameters. We observed a sharp resonance peak due to the transitions between the S = 11 quantum levels and a broadband corresponding to a distribution of resonance peaks due to the ZFS of the S = 12 quantum levels. By analyzing HF-ESR spectra, we confirm the expected S = 12 ground state and determine its ZFS parameter D as −0.069 K, and, furthermore, we reproduce the spectra recorded at 154 GHz. The macrospin model proves to still be valid. The ZFS is attributed to the axial magnetic anisotropy, as found in some other Cr-based molecular wheels. The detailed HF-ESR investigation presented in this paper will benefit the studies on other {Cr8Ln8} wheels with magnetic Ln3+ ions and highlights the importance of the HF-ESR method as a high-resolution probe in determining the ZFS parameters with very small magnitude. [ABSTRACT FROM AUTHOR]

Abstract An important vision of modern magnetic research is to use antiferromagnets (AFMs) as controllable and active ultrafast components in spintronic devices. Hematite (α‐Fe2O3) is a promising model material in this respect because its pronounced Dzyaloshinskii‐Moriya interaction leads to the coexistence of antiferromagnetism and weak ferromagnetism. Here, femtosecond laser pulses are used to drive terahertz (THz) spin currents from α‐Fe2O3 into an adjacent Pt layer. Two contributions to the generation of the spin current with distinctly different dynamics are found: the impulsive stimulated Raman scatting that relies on the AFM order and the ultrafast spin Seebeck effect that relies on the net magnetization. The total THz spin current dynamics can be manipulated by a medium‐strength magnetic field below 1 T. The control of the THz spin current achieved in α‐Fe2O3 opens the pathway toward tailoring the exact spin current dynamics from ultrafast AFM spin sources.

Abstract Based on magneto‐electric (ME) effect and spin Hall effect (SHE), the authors propose a novel spin logic device named MESH‐SLD. In MESH‐SLD, the charge current is transmitted in the channel by employing inverse SHE, which solves the dissipation problem of spin current in the channel of all‐spin logic device (ASLD). By using a magnetization‐dynamics/spin‐transport hybrid model, the authors have investigated the influence of working voltage, channel lengths, and materials on the performance of the MESH‐SLD. And the simulation results show that the energy dissipation of the MESH‐SLD only increases approximately linearly with the increase of channel length, while the switching delay remains almost unchanged. In addition, with the increase of the spin Hall angle of the channel material, the energy dissipation and the minimum working voltage of the MESH‐SLD decrease significantly. Most importantly, compared with conventional ASLD, the proposed MESH‐SLD improve the switching delay and the energy dissipation by about 2.5 times and 851.8 times, respectively.

Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetisation patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using superconducting quantum interference devices, spin centre and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoscale magnetic resonance imaging. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, three-dimensional and geometrically curved objects of different material classes including two-dimensional materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.

We perform an ab initio non-adiabatic molecular dynamics simulation to investigate the non-equilibrium spin and electron dynamics in a prototypical topological insulator (TI) Bi2Se3. Different from the ground state, we reveal that backscattering can happen in an oscillating manner between time-reversal pair topological surface states (TSSs) in the non-equilibrium dynamics. Analysis shows the phonon excitation induces orbital composition change by electron-phonon interaction, which further stimulates spin canting through spin-orbit coupling. The spin canting of time-reversal pair TSSs leads to the non-zero non-adiabatic coupling between them and then issues in backscattering. Both the spin canting and backscattering result in ultrafast spin relaxation with a timescale around 100 fs. This study provides critical insights into the non-equilibrium electron and spin dynamics in TI at the ab initio level and paves a way for the design of ultrafast spintronic materials.

In this work, we tackle the problem of the spatially selective optical excitation of spin dynamics in structures with multiple magnetic layers. The 120 fs circularly polarized laser pulses were used to launch magnetization precession in an all-dielectric magneto-photonic crystals (MPC) formed by magnetic layers sandwiched between and inside two magnetic Bragg mirrors. Optical pump-probe experiments reveal magnetization precession triggered via ultrafast inverse Faraday effect with an amplitude strongly dependent on the pump central wavelength: maxima of the amplitude are achieved for the wavelength tuned at the cavity resonance and at the edge of the photonic bandgap. The optical impact on the spins caused by the inverse Faraday effect and spectrum of this effect are found to correlate mostly to the direct Faraday effect. We show that even though the pump laser pulses propagate along the whole structure tuning their wavelength allows localization of a larger spin precession either in the cavity layer or in the Bragg mirror layers selectively. The results pave the way to the ultrafast optical control of magnetization dynamics at a sub-wavelength scale that is vital for modern magneto-photonics and magnonics.

Abstract Fast spin manipulation in magnetic heterostructures, where magnetic interactions between different materials often define the functionality of devices, is a key issue in the development of ultrafast spintronics. Although recently developed optical approaches such as ultrafast spin‐transfer and spin–orbit torques open new pathways to fast spin manipulation, these processes do not fully utilize the unique possibilities offered by interfacial magnetic coupling effects in ferromagnetic multilayer systems. Here, ultrafast optically controlled interfacial exchange interactions in the ferromagnetic Co2FeAl/(Ga,Mn)As system at low laser fluence levels are experimentally demonstrated. The excitation efficiency of Co2FeAl with the (Ga,Mn)As layer is 30–40 times higher than the case with the GaAs layer at 5 K due to the modification of exchange coupling interaction via photoexcited charge transfer between the two ferromagnetic layers. In addition, the coherent spin precessions persist to room temperature, excluding the drive of pump‐modulated magnetization in the (Ga,Mn)As layer and indicating a proximity‐effect‐related optical excitation mechanism. The results highlight the importance of interfacial exchange interactions in ferromagnetic heterostructures and how these magnetic coupling effects can be utilized for ultrafast, low‐power spin manipulation.

Manipulation of the optical spin orientation in semiconductors is a key technology for realizing spin‐based photoelectric information processing. Application of magnetic field is a simple method to control the spin polarization degree through Zeeman splitting. However, this effect can only be achieved at cryogenic temperatures and in a strong magnetic field. Here, room‐temperature voltage control of optical polarization in the range of 3–15%, corresponding to a 12–60% change in relative spin polarization is demonstrated. For this, a III‐V semiconductor quantum dot tunnel coupled with a quantum well spin reservoir is used. The spin‐flip scattering rate within quantum dots is electric‐field‐controlled in the time domain of several tens of picoseconds. This is achieved by precise control of the tunnel injection efficiency of electrons and holes via coupled potential modification. The findings will pave the way for the generation of ultrafast spin‐modulated optical signals by the electric field effect. [ABSTRACT FROM AUTHOR]

Microwave spin resonance behaviour of Sr2+ doped Zirconium ferrite Zr 1-x Sr x Fe 2 O 4 ; (0 ≤ x ≥ 0.20) nanoparticles synthesized by auto combustion route has been investigated by electron paramagnetic resonance (EPR) which show a broad ferromagnetic resonance signal with a superimposed hump signal which is attributed to ferrite Fe3+ ions and oxygen vacancies which is in agreement with XRD and XPS. EPR shows low spin concentration and smaller relaxation time for Zr 0.80 Sr 0.20 Fe 2 O 4 which can be used for hyperthermia and for use as a MRI contrast agent. EDS and XPS confirms the presence of Zr, Sr, Fe, O, and C and HRTEM images confirm growth along (220) and (311) with an interatomic distance of 0.3327 nm and 0.2622 nm respectively, thus, authenticating the formation of spinel structure in agreement with FTIR studies. The magnetic behaviour (M − H loop) shows high saturation magnetization and higher value of effective magnetocrystalline anisotropy (K e f f) for Zr 0.80 Sr 0.20 Fe 2 O 4. [Display omitted] [ABSTRACT FROM AUTHOR]

The site-specific signal enhancement provided by parahydrogen induced polarization (PHIP) may be combined with magnetic resonance imaging (MRI) to study chemical and biomolecular processes. However, imaging of hydrogen nuclei ( 1 H) is hampered by background signals arising from the presence of thermally polarized nuclei. Additionally, fast imaging sequences are commonly based on multiple radio-frequency pulses, where the signals resulting from PHIP oscillate due to the evolution with a J -coupling Hamiltonian. In this article, an innovative imaging scheme for single-scan MRI is presented that effectively detects hyperpolarized components while simultaneously canceling out thermal contributions. This method is based on the quenching of inherent oscillations of PHIP-originated signals due to J -couplings during the multipulse sequence and the suppression of thermal signals by spin dynamics and a tailored restructuring of the k -space. A series of numerical simulations on specific two- and three-spin systems serve to support the feasibility of the approach. Furthermore, this theoretical study demonstrates the potential of combining hyperpolarization and long-lived states (PHIP and LLS) in the selected molecules, which could be seen as a preliminary step towards the development of fast imaging techniques, for example in the field of biomolecular research. [Display omitted] • A strategy to background-free single-scan PHIP-MRI is proposed. • The acquisition scheme effectively cancels thermal contributions. • Numerical simulations validate method's efficacy in two and three-spin systems. • Illustrative example of a combination of PHIP and singlet state NMR (LLS). • High contrast images in deuterated and protonated solvents for in vivo application. [ABSTRACT FROM AUTHOR]

Floquet–Magnus and Fer expansion (FE) schemes are used in nuclear magnetic resonance (NMR) for the calculation of effective Hamiltonians and propagators. This work focuses on applying the Floquet–Magnus and FE approaches to control the spin system evolution during the phase modulate Lee–Goldburg radiation experiment. Until now, the Frequency switched Lee–Goldburg and its variant called the Phase module Lee–Goldburg have been treated by only the average Hamiltonian theory and the bimodal Floquet approach. In this paper, we use the two developing expansion schemes in solid-state NMR for the calculation of the effective Hamiltonian and propagator during the spin dynamics. Our work unifies and generalizes existing results of the Floquet–Magnus and FEs and delivers illustrations of novel springs that boost previous applications that are based on the classical information. The generality of this work points to potential applications in problems related to solid-state NMR and theoretical developments of spectroscopy as well as interdisciplinary research areas whenever they include spin dynamics concepts.

Spin relaxation induced by the interfacial effects in GaN/Al0.25Ga0.75N heterostructures was carefully investigated using a photon-energy-dependent time-resolved Kerr rotation spectrum. The existence of the interfacial localized states with potential fluctuations at the GaN/AlGaN heterointerface leads to photoluminescence peaks showing blue and S-shaped shifts owing to the excitation power and temperature, respectively. Photoexcited electrons in the localized states show a spin relaxation time longer than 1 ns because of the suppression of the D'yakonov–Perel’ (DP) scattering, while the spin relaxation time of free electrons was approximately only 10 ps because of the giant Rashba spin-orbit coupling induced by the interfacial polarization field under the framework of the DP scattering mechanism. Furthermore, it is found that the high electron mobility at the heterointerface results in a long spin diffusion length of 300 nm at high temperatures, which is promising for the development of GaN-based spintronic devices.

To quantitatively characterize the behaviors of a spin-12 particle moving on a rotating curved surface and in a time-varying field, we derived the Schrödinger equation of the particle on the surface with the induced Pauli matrices based on the local curvilinear coordinate. To consider the relativistic effects, Minkowski space M is employed. Based on the solution of the Schrödinger equation, we found that the evolution of phase is influenced by the coupling of external fields and the geometry of surfaces as well as the relativistic effect originating from rotation. As examples, the solutions on a rotating cylinder/sphere in a damping magnetic field are calculated. The spin-flip behavior of the particle and the effects of external field and rotation are demonstrated. The results may help stimulate the ideas of modulating and controlling the spin on nano-surfaces.

The spin dynamics in magnetically disordered GdCu2 nanoparticles, varying the nanoparticle size in the range 53 to 7 nm, has been scrutinized. Dynamic χAC susceptibility measurements have revealed the existence of dissipation at Tg = 18 K, which is associated to the spin freezing transition, for all the ensembles. Besides, the superantiferromagnetic ensembles (〈D〉≥ 24 nm) also showcase a dissipation contribution close to the vicinity of the Néel transition, TN = 40.2 K. This dissipation, which takes the form of two humps located at Td1 = 33.5(5) K and Td2 = 40.0(5) K, is associated to uncompensated antiferromagnetic moments. Time-dependent phenomena (ageing and memory effects) are only evidenced below the spin freezing transition, evidencing that solely this low-temperature disordered phase is driven by the frustration of RKKY exchange interactions. Consequently, GdCu2 nanoparticles display a dual disorder-driven magnetic dynamics, which are the one ascribed to the magnetically frustrated moments located at the nanoparticle surface; and that of uncompensated antiferromagnetic moments located within the nanoparticle core. [ABSTRACT FROM AUTHOR]

Ensembles of negatively charged nitrogen-vacancy centers (NV−) in diamond have been proposed for sensing of magnetic fields and paramagnetic agents, and as a source of spin-order for the hyperpolarization of nuclei in magnetic resonance applications. To this end, strongly fluorescent nanodiamonds (NDs) represent promising materials, with large surface areas and dense ensembles of NV−. However, surface effects tend to favor the less useful neutral form, the NV0 centers, and strategies to increase the density of shallow NV− centers have been proposed, including irradiation with strong laser power (Gorrini in ACS Appl Mater Interfaces. 13:43221–43232, 2021). Here, we study the fluorescence properties and optically detected magnetic resonance (ODMR) of NV− centers as a function of laser power in strongly fluorescent bulk diamond and in nanodiamonds obtained by nanomilling of the native material. In bulk diamond, we find that increasing laser power increases ODMR contrast, consistent with a power-dependent increase in spin-polarization. Conversely, in nanodiamonds we observe a non-monotonic behavior, with a decrease in ODMR contrast at higher laser power. We hypothesize that this phenomenon may be ascribed to more efficient NV−→NV0 photoconversion in nanodiamonds compared to bulk diamond, resulting in depletion of the NV− pool. A similar behavior is shown for NDs internalized in macrophage cells under the typical experimental conditions of imaging bioassays. Our results suggest strong laser irradiation is not an effective strategy in NDs, where the interplay between surface effects and local microenvironment determine the optimal experimental conditions. [ABSTRACT FROM AUTHOR]

State transition in the multiple-levels system has the great potential applications in the quantum technology. In this article we employ a deterministic approach in complex space to analyze the dynamics of the 1s–2p electron transition in the hydrogen atom. The electron's spin motion is embodied in the framework of quantum Hamilton mechanics that allows us to examine the transition dynamics more precisely. The transition is driven by an oscillating electric field in the z-direction. The electron's transition process can be visualized by monitoring its motion in the complex space. The quantum potential and the total energy proposed in this paper provide new indices to observe the dynamic changes of electrons in the transition process. [ABSTRACT FROM AUTHOR]

We have investigated the magnetization reversal mechanism and dynamic behaviour of 90 nm wide permalloy nanowires patterned over a large area as a function of thickness (t) in the range from 20 nm to 70 nm and applied field orientation. The reversal processes and dynamic properties are probed using the magneto-optical Kerr effect and broadband ferromagnetic resonance (FMR) spectroscopy respectively. We have observed that both the static and dynamic properties are markedly sensitive to the film thickness. For t = 20 nm, the magnetization reversal process is dominated by coherent rotation mode due to the strong shape anisotropy and the onset of curling mode is observed. The FMR spectra display the existence of two well-separated modes, unlike the single mode which existed in the large width nanowires of the same thickness. The two modes at high and low frequencies correspond to the excitations at the centre and edges of the wire respectively. For t â©ľ 50 nm, the magnetization reversal process is dominated by curling mode of reversal. The centre mode frequency is found to be sensitive to the film thickness and shows two fold anisotropy. The experimental results are substantiated with micromagnetic simulations. These results have potential implications in designing reconfigurable magnonic crystals for microwave devices. [ABSTRACT FROM AUTHOR]