Spin Switching Research Articles

Mechanisms for the Spin-State Switching of Strapped Ni-Porphyrin Complexes Deposited on Metal Surfaces: Insights from Quantum Chemical Calculations.

The incorporation of molecular switches on nanodevices requires both the intactness of the molecule once deposited on a substrate and the persistence of the reversible switching feature. Recently, the reversible spin-switching of strapped Ni(II)-porphyrin complexes deposited on Ag(111) surface is demonstrated with low-temperature scanning tunneling microscopy (STM). The spin transition is accompanied by the coordination change of the metal center, a phenomenon denominated in coordination-induced spin-state switching (CISSS). In this contribution, the spin switching of the deposited strapped Ni-porphyrin molecules using different quantum chemistry approaches is explored. This calculations inform about the geometry and electronic structure of the adsorbed molecules and the origin of the voltage-dependent switching promoted by the STM tip. Two different mechanisms are inspected to elucidate the key role of the tip, mainly the electron injection between the tip and the molecule and the differential stabilization of the two spin states by the applied electric field between the tip and the silver surface. This study puts in evidence the relevance of the pyridine ligand contained in the strap in the transport properties as in the CISSS process itself.

Spin switching in Sm0.7Er0.3FeO3 triggered by terahertz magnetic-field pulses.

Driving spin systems to states far from equilibrium is indispensable in investigations of functional nonlinearities of antiferromagnets for spintronics. So far, it has been shown that electric-field pulses in the spectral region from the visible to the terahertz range can be used to induce ultrafast switching between different spin states. Here we demonstrate that a multicycle terahertz magnetic-field pulse can be used to induce non-thermal spin switching in antiferromagnets. When a strong pulse is applied to Sm0.7Er0.3FeO3, the magnetic order parameter is first driven away from the barrier between the two potential minima of this antiferromagnet and then, in the subsequent inertial motion towards the opposite direction, it crosses the barrier. Our analysis reveals that the initial motion is driven by a dynamical modification of the magnetic potential, and this modification is enhanced through coupling between the two magnon modes.

Giant and negative magnetoresistances in conical magnets in the nonequilibrium Boltzmann equation approach

We study magnetotransport in conical helimagnet crystals using the nonequilibriun Boltzmann equation approach. Spin dependent magnetoresistance exhibits dramatic properties for high and low electron concentrations at different temperatures. For spin up electrons we find negative magnetoresistance despite only considering a single carrier type. For spin down electrons we observe giant magnetoresistance due to depletion of spin down electrons with an applied magnetic field. For spin up carriers, the magnetoresistance is negative, due to the increase in charge carriers with a magnetic field. In addition, we investigate the spin dependent Hall effect. If a magnetic field reaches some critical value for spin down electrons, giant Hall resistance occurs, i.e. Hall current vanishes. This effect is explained by the absence of spin down carriers. For spin up carriers, the Hall constant dramatically decreases with field, due to the increase in spin up electron density. Because of the giant spin dependent magnetoresistance and Hall resistivity, conical helimagnets could be useful in spin switching devices.

Mn doping-induced twofold spin reorientation and multi-step spin switching in NdFeO3 single crystal

Magnetization reversal and magnetic state regulation are the basis of application for magnetic materials in information processing. Here, twofold spin reorientation transitions (SRT) and field-induced multi-step spin switching phenomena were observed in NdMn0.2Fe0.8O3 (NMFO) single crystals grown via the optical floating zone method. Magnetic anisotropy was systematically investigated in both Zero-Field-Cooled (ZFC) and Field-Cooled (FC) modes. The NMFO single crystal exhibited twofold SRTs: from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) and from Γ1 (Ax, Gy, Cz) to Γ2 (Fx, Cy, Gz). Furthermore, a magnetic field-induced spin reorientation transition was identified along the c-axis. Additionally, closer proximity to the SRT temperature corresponded to a reduced magnetic field requirement for inducing the spin reorientation transition. These findings contribute to our comprehension of spin dynamics in NMFO, presenting possibilities for future device applications.

Highly switchable photonic spin hall effect in vanadium dioxide grating structure

The enhancement and manipulation of the photonic spin Hall effects are essential for the spin photonic applications. The emergence of the phase transition material, vanadium dioxide (VO2), presents a unique chance to explore its conductivity dependent optical properties. However, the explorations on the PSHEs in VO2 based microstructures are quite rare. Here, we report the enhanced and controllable reflected photonic spin Hall effects under the horizontal or vertical polarized wave by establishing the VO2 grating structure. It can be found that associated with the phase transition of VO2, its changed conductivity not only tunes the magnitude of the reflected spin shift but also changes its sign, which even results in a dramatic modulation of the reflected spin shift from the negative maximum value under the vertical polarized wave to the positive maximum value under the horizontal polarized wave at the specific wavelength. Such features can be attributed to the dramatic changes of the reflectances in the VO2 grating structure under different polarizations induced by the changed conductivity of VO2. Our results allow the actively alternative phase transition material based configurations capable of dramatic manipulation of the reflected spin shifts and it constitutes a significant step toward highly switchable spin photonic devices.

Ultrafast antiferromagnetic switching of Mn2Au with laser-induced optical torques

Ultrafast manipulation of the Néel vector in metallic antiferromagnets most commonly occurs by generation of spin-orbit (SOT) or spin-transfer (STT) torques. Here, we predict another possibility for antiferromagnetic domain switching by using novel laser optical torques (LOTs). We present results of atomistic spin dynamics simulations from the application of LOTs for all-optical switching of the Néel vector in the antiferromagnet Mn2Au. The driving mechanism takes advantage of the sizeable exchange enhancement, characteristic of antiferromagnetic dynamics, allowing for picosecond 90 and 180-degree precessional toggle switching of the Néel vector with laser fluences on the order of mJ/cm2. A special symmetry of these novel torques greatly minimises the over-shooting effect common to precessional spin switching by SOT and STT methods. We demonstrate the opportunity for LOTs to produce deterministic, non-toggle switching of single antiferromagnetic domains. Lastly, we show that even with sizeable ultrafast heating by laser in metallic systems, there exist a large interval of laser parameters where the LOT-assisted toggle and preferential switchings in magnetic grains have probabilities close to one. The proposed protocol could be used on its own for all-optical control of antiferromagnets for computing or memory storage, or in combination with other switching methods to lower energy barriers and/or to prevent over-shooting of the Néel vector.

Tunable Anomalous Hall Effect in a Kagomé Ferromagnetic Weyl Semimetal.

Emerging from the intricate interplay of topology and magnetism, the giant anomalous Hall effect (AHE) is the most known topological property of the recently discovered kagomé ferromagnetic Weyl semimetal Co3Sn2S2 with the magnetic Co atoms arranged on a kagomé lattice. Here it is reported that the AHE in Co3Sn2S2 can be fine-tuned by an applied magnetic field orientated within ≈2° of the kagomé plane, while beyond this regime, it stays unchanged. Particularly, it can vanish in magnetic fields parallel to the kagomé plane and even decrease in magnetic fields collinear with the spin direction. This tunable AHE can be attributed to local spin switching enabled by the geometrical frustration of the magnetic kagomé lattice, revealing that spins in a kagomé ferromagnet change their switching behavior as the magnetic field approaches the kagomé plane. These results also suggest a versatile way to tune the properties of a kagomé magnet.

Chemically Separable Co(II) Spin-State Isomers.

The phenomenon of spin crossover involves coordination complexes with switchable spin states. This spin state change is accompanied by significant geometric changes such that low and high spin forms of a complex are distinct isomers that exist in equilibrium with one another. Typically, spin-state isomers interconvert rapidly and are similar enough in polarity to prevent their independent separation and isolation. We report here the first example, to our knowledge, of cobalt(II) spin-state isomers that can be physically separated. The reaction of Mo2(dpa)4 (dpa = 2,2'-dipyridylamide) with CoBr2 produces a mixture of two heterometallic compounds with a linear, metal-metal-bonded Mo[Formula: see text]Mo-Co chain. The complexes, SC-[BrMo2(dpa)4Co]Br (SC-2) and HS-[BrMo2(dpa)4CoBr] (HS-2), have identical compositions (Mo2Co(dpa)4Br2) but different ground spin states and coordination geometries of the Co(II) ion. In the solid state, SC-2 undergoes incomplete spin crossover from an S = 1/2 state to an S = 3/2 state, and HS-2 has a high spin, S = 3/2, ground state, as confirmed by SQUID magnetometry and EPR spectroscopy. Crystallographic analyses of SC-2 and HS-2 show that SC-2 has an elongated Co-Br distance relative to HS-2 and is best described as the salt [BrMo2(dpa)4Co]Br. This limits SC-2's solubility in nonpolar solvents and allows for the physical separation of the two isomers. Solution studies of SC-2 and HS-2 indicate that SC-2 and HS-2 interconvert slowly relative to the NMR time scale. Additional solution-state EPR and UV-vis absorption measurements demonstrate that the choice of solvent polarity determines the predominant isomer present in solution.

Room temperature polariton spin switches based on Van der Waals superlattices

Transition-metal dichalcogenide monolayers possess large exciton binding energy and a robust valley degree of freedom, making them a viable platform for the development of spintronic devices capable of operating at room temperature. The development of such monolayer TMD-based spintronic devices requires strong spin-dependent interactions and effective spin transport. This can be achieved by employing exciton-polaritons. These hybrid light-matter states arising from the strong coupling of excitons and photons allow high-speed in-plane propagation and strong nonlinear interactions. Here, we demonstrate the operation of all-optical polariton spin switches by incorporating a WS2 superlattice into a planar microcavity. We demonstrate spin-anisotropic polariton nonlinear interactions in a WS2 superlattice at room temperature. As a proof-of-concept, we utilize these spin-dependent interactions to implement different spin switch geometries at ambient conditions, which show intrinsic sub-picosecond switching time and small footprint. Our findings offer new perspectives on manipulations of the polarization state in polaritonic systems and highlight the potential of atomically thin semiconductors for the development of next generation information processing devices.

Effect of the Solvent Nature on a Spin Equilibrium in the Solutions of the Phenylboron-Capped Hexa-n-Butylsulfide Cobalt(II) Clathrochelate Stadied by the Paramagnetic NMR Spectroscopy

A spin state of the phenylbon-capped hexa-n-butylsulfide cobalt(II) clathrochelate in solutions was studied by paramagnetic NMR spectroscopy. This cage complex is found to undergo the temperature – induced spin crossover in solvents of different nature (acetonitrile, chloroform, dichloromethane, and benzene). The previously developed method for an analysis of paramagnetic shifts in NMR spectra allows to calculate of the thermodynamic parameters (enthalpy and entropy) of a given spin equilibrium in the solutions. In spite of the conformational rigidity of the macrobicyclic tris-α-dioximate molecules, the substantial changes in their electronic structures and spin crossover parameters were observed, being affected by a polarity of the solvent used. This provides an opportunity for the fine tuning of spin switch characteristics by changing this medium parameter.

Creation of spin switching in graphene oxide-based hybrid film materials with an anionic Fe(III) 5Cl-salicyaldehyde-thiosemicarbazone complex.

The present article describes the synthesis of hybrid composite film materials formed during the self-assembly process through non-covalent interactions of graphene oxide (GO) nanosheets with salt 1, represented by an anionic spin-crossover complex [FeIII(5Cl-thsa)2]- (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) and the organic tetraethylammonium cation [Et4N]+. The insertion of the salt 1 molecules into the interlayer space of GO nanosheets with the subsequent formation of a hybrid material GO-1 was observed. The film of the hybrid material GO-1 was characterized by scanning electron and confocal laser microscopy, EDX and XPS analysis, IR, Raman and 57Fe Mössbauer spectroscopy, dc magnetic measurements, and powder X-ray diffraction. Comparison of the magnetic properties of salt 1 and a film of the hybrid material GO-1 demonstrated a significant influence of the GO nanosheets matrix on the completeness of spin transition and showed a slight shift of the hysteresis loop by 1 K in the temperature range of 200-230 K. DFT calculations showed an important role of the organic cation [Et4N]+ in the process of adsorption of the spin-crossover anion [FeIII(5Cl-thsa)2]- on the GO nanosheet surface.

A Spin–Orbit Torque Knob to Tailor Stochasticity for Physically Secured Applications

AbstractThe deterministic switching of spin–orbit torque (SOT) memory has long been the primary challenge for implementation. Conversely, stochastic switching has recently sparked significant interest for physically secured applications. This study investigates the effects of an external field (Hx) applied to break the SOT symmetry for deterministic switching in a Pt/Co bilayer with perpendicular anisotropy. This external field serves as a tuning mechanism to adjust the stochasticity at the intermediate state during SOT switching. It is observed that moderate Hx could lead to a substantial variation in electrical output during the repeating write/read operations. In contrast, a large Hx enables precise control over the intermediate states of the Pt/Co bilayer, effectively functioning as a memristor. The stochasticity derives from small Hx resulting from the dynamics of dendritic domain wall propagation during SOT switching. Herein, the oblique domain spiking from the initially reversed domain is notably influenced by the transverse component of SOT. Increasing Hx suppresses this oblique dendritic domain growth, allowing for controllable domain propagation and reducing stochasticity. By utilizing Hx as an external knob to tailor the stochasticity at the intermediate state, the high stochastic state can be employed as an ideal entropy source for an SOT‐based random number generator.

Strong Electron-Vibration Signals in Weakly Coupled Molecular Junctions: Activation of Spin-Crossover.

Manipulating individual molecular spin states with electronic current has the potential to revolutionize quantum information devices. However, it is still unclear how a current can cause a spin transition in single-molecule devices. Here, we propose a spin-crossover (SCO) mechanism induced by electron-phonon coupling in an iron(II) phthalocyanine molecule situated on a graphene-decoupled Ir(111) substrate. We performed simulations of both elastic and inelastic electron tunneling spectroscopy (IETS), which reveal current-induced Fe-N vibrations and an underestimation of established electron-vibration signals. Going beyond standard perturbation theory, we examined molecules in various charge and spin states using the Franck-Condon framework. The increased probability of spin switching suggests that notable IETS signals indicate SCO triggered by the inelastic vibrational excitation associated with Fe-N stretching.

Predictable Gate-Field Control of Spin in Altermagnets with Spin-Layer Coupling.

Spintronics, a technology harnessing electron spin for information transmission, offers a promising avenue to surpass the limitations of conventional electronic devices. While the spin directly interacts with the magnetic field, its control through the electric field is generally more practical, and has become a focal point in the field. Here, we propose a mechanism to realize static and almost uniform effective magnetic field by gate-electric field. Our method employs two-dimensional altermagnets with valley-mediated spin-layer coupling (SLC), in which electronic states display valley-contrasted spin and layer polarization. For the low-energy valley electrons, a uniform gate field is approximately identical to a uniform magnetic field, leading to predictable control of spin. Through symmetry analysis and abinitio calculations, we predict altermagnetic monolayer Ca(CoN)_{2} and its family materials as potential candidates hosting SLC. We show that an almost uniform magnetic field (B_{z}) indeed is generated by gate field (E_{z}) in Ca(CoN)_{2} with B_{z}∝E_{z} in a wide range, and B_{z} reaches as high as about 10^{3} T when E_{z}=0.2 eV/Å. Furthermore, owing to the clean band structure and SLC, one can achieve perfect and switchable spin and valley currents and significant tunneling magnetoresistance in Ca(CoN)_{2} solely using the gate field. Our work provides new opportunities to generate predictable control of spin and design spintronic devices that can be controlled by purely electric means.

Unipolar spin diodes and unipolar spin switches by Spin-Transfer torque in doped graphether

Spin switches are a fundamental component in the majority of spintronic devices, and have found extensive application in data storage, logical data manipulation, and signal processing. An essential aspect of constructing a spin switch is determining a stable two-dimensional material, which is easy to control and produce. Theoretical studies have shown that graphether is particularly promising due to its exceptionally high melting point and outstanding air stability. The band structure can be modified by doping, making it an important material for spin switch applications. In this paper, we have calculated the electromagnetic properties of doped graphether by first principles. Then we select a modified graphether with P-type and N-type doping configurations to construct magnetic tunnel junctions (MTJ). The results show that the MTJ exhibits perfect highly efficient spin switch as a result of spin reversal induced by spin-transfer torque (STT). In addition, our designed MTJ shows a remarkable rectification effect and spin filtering effect (SFE). According to our calculations, the modified graphether materials also show promise as two-dimensional spintronics materials.

Spin vacuum switching.

Ultrafast control over the magnetic orientation of matter represents a vital element of potential future spin-based electronics ("spintronics"). While physical mechanisms underpinning spin switching are established for picosecond time scales, we here present a physical route to magnetization toggle control, i.e., multiple switching events, at <100 femtoseconds. A minority spin current injected into a ferromagnet is shown to generate rapid depopulation of the minority channel below the ground-state Fermi level, creating a minority "spin vacuum" that then drives rapid charge redistribution from the majority channel and spin switching. We demonstrate that this mechanism reproduces many of the features of recent subpicosecond switching of ferromagnetic Co/Pt multilayers and provide simple practical rules for the design of materials via tailoring the electronic density of states to optimize spin vacuum control over magnetic order.

Robust free-base and metalated corrole radicals with reduction-induced emission

Preparing free-base porphyrinoid radicals that can function as coordination ligands is a challenging task. Here we report the synthesis of a stable, free-base benzocorrole (BC) radical containing only two inner NH protons via a retro-Diels-Alder conversion. The radical character of BC was fully supported by crystallographic analysis, spectroscopic evidence, and theoretical calculations. This neutral radical ligand allowed easy insertion of Zn(II), Ga(III), and Pd(II) ions to produce radical complexes. All these radicals exhibited luminescence-on responses under weak reducing atmosphere, corresponding to the conversion to their aromatic anions. The red fluorescence was observed for BC and its Zn(II) and Ga(III) complexes, and the near-infrared phosphorescence (> 900 nm) was detected for Pd(II) complex at room temperature. Furthermore, Ga(III) corrole exhibited a variation in fluorescence in response to axial coordination. Our findings provide a promising radical platform for coordination and developing novel functional materials with switchable spin and emission.

Theoretical Study for Spin Transport properties of FM-(G/C)10- FM

In the present study, we propose a physical model to study spin transport through DNA system and provide apparent physical mechanism for spin dependent phenomenon. The system considered in our work is DNA bases guanine-cytosine coupled to two ferromagnetic leads (FM-(G/C)10-FM) in parallel and anti-parallel configuration case, throughout magnetic quantum contacts. Our treatment is based on the tight binding model to derive obvious formula for the transmission spectrum which is employed to investigate the spin dependent current-bias voltage characteristics and the temperature - Conductance dependence. Our calculations of for strong, weak and without backbone regimes. Various factors are involved in our -study. These are the electrical contacts between DNA molecules and electrodes, the structure of DNA molecule and the environment around DNA molecule. The system spin dependent factors, that are investigated extensively in our study include the spin dependent coupling between subsystems, the quantum contacts between active region and electrodes, majority and minority electrons spin in the ferromagnetic leads as well as externally applied bias voltage. Variation of these factors can enhanced or suppressed spin transport through (G/C)10 molecule. The transmission spectrum calculations conform that the spin transport throughout (G/C)10 originates by a coherent tunneling process between neighboring bases through the overlapping of the LUMO orbitals of the bases. Our results showed that the spin-polarized transport that can be effectively regulated by the type of regime as well as the spin configuration in the leads which can exhibit efficient spin filtering and spin switching by employing the spin blockade phenomenon

Spin switching in Er1-xSmxFeO3 (x = 0, 0.2) single crystals

We investigated spin-switching transitions in Er1-xSmxFeO3 (x = 0, 0.2) single crystals and variations in spin configurations with the applied field. The crystals were grown using the optical floating zone technique, and the magnetic properties were measured under field-cooled cooling (FCC) and field-cooled warming (FCW) protocols. The crystals exhibit field-dependent variation in the spin-switching temperature. In FCC, spin switching temperature increases with a magnetic field. However, in FCW, the spin-switching temperature (TSSW) rises initially with an increasing magnetic field, reaches a maximum value and later decreases when field strengths are high. We observe that spin switching depends not only on the magnitude of the externally applied magnetic field but also on the starting temperature of FCC. The magnetic and thermal history of the sample has a critical role in this phenomenon. A phase diagram (magnetic field-TSSW) constructed using the FCC and FCW data helps to illustrate various magnetic configurations. The FCC and FCW measurements in the a-direction of ErFeO3 at high fields (2T, 3T) suggest that spin switching, which involves the reversal of spins, does not occur. Instead, there is a change in the magnitude of the weak ferromagnetic moment, and rare earth spins below the compensation temperature (Tcomp).

Supercurrent-induced spin switching via indirect exchange interaction

Supercurrent-induced spin switching via indirect exchange interaction