Modulation Of Spin Polarization Research Articles

Enhanced Oxygen Evolution and Zinc-Air Battery Performance via Electronic Spin Modulation in Heterostructured Catalysts.

Beyond optimizing electronic energy levels, the modulation of the electronic spin configuration is an effective strategy, often overlooked, to boost activity and selectivity in a range of catalytic reactions, including the oxygen evolution reaction (OER). This electronic spin modulation is frequently accomplished using external magnetic fields, which makes it impractical for real applications. Herein, spin modulation is achieved by engineering Ni/MnFe2O4 heterojunctions, whose surface is reconstructed into NiOOH/MnFeOOH during the OER. NiOOH/MnFeOOH shows a high spin state of Ni, which regulates the OH- and O2 adsorption energy and enables spin alignment of oxygen intermediates. As a result, NiOOH/MnFeOOH electrocatalysts provide excellent OER performance with an overpotential of 261 mV at 10 mA cm-2. Besides, rechargeable zinc-air batteries based on Ni/MnFe2O4 show a high open circuit potential of 1.56 V and excellent stability for more than 1000 cycles. This outstanding performance is rationalized using density functional theory calculations, which show that the optimal spin state of both Ni active sites and oxygen intermediates facilitates spin-selected charge transport, optimizes the reaction kinetics, and decreases the energy barrier to the evolution of oxygen. This study provides valuable insight into spin polarization modulation by heterojunctions enabling the design of next-generation OER catalysts with boosted performance.

Observation of spin polarization modulation responses of injection-locked vertical-cavity surface-emitting lasers

We report on the modulation responses of an injection-locked vertical-cavity surface-emitting laser (VCSEL) measured using an optical spin-polarization modulation technique. We reveal that weak injection locking is suitable to maintain a strong resonance response at a high-frequency region depending on the linear birefringence of the VCSEL, a unique feature of spin-polarization modulation response. The measured results can be reasonably reproduced with simulated ones on the basis of spin-flip rate equations. Our findings support novel applications of spin-controlled VCSELs with injection locking.

Unveiling the Coercivity-Induced Electrocatalytic Oxygen Evolution Activity of Single-Domain CoFe2O4 Nanocrystals under a Magnetic Field.

Spin polarization modulation in ferromagnetic materials has become an effective way to promote the electrocatalytic oxygen evolution reaction (OER). Herein, to reveal the coercivity-related OER performance, single-domain ferromagnetic CoFe2O4 (CFO) nanocrystals with different coercivities are synthesized and subjected to OER under an in situ tunable magnetic field. As the more ordered spin polarization state of CFO with a higher coercivity can afford a facilitated electron transfer process, the magnetic field-assisted OER activity can be more improved with an increase in coercivity. Specifically, the decreased magnitudes of the overpotential, Tafel slope, and charge transfer resistance increase on the samples with higher coercivity. The CFO with the largest coercivity (7500 Oe) shows the best OER performance with an overpotential of 350 mV at a current density of 10 mA cm-2 under a magnetic field of 14000 G. In addition, a hysteresis effect that maintains enhanced OER current density after the magnetic field has been withdrawn is observed, where higher coercivity affords a longer hysteresis period. The exploration of coercivity-related OER enhancement may provide new insights into the design and synthesis of promising "magnetic effect" catalysts.

Selective measurement of the longitudinal electron spin relaxation timeT1ofCe3+ions in a YAG lattice: Resonant spin inertia

Electron spin oriented along an external magnetic field is subject to longitudinal spin relaxation with characteristic time $T_1$. The corresponding decay is nonoscillating, so one cannot readily ascribe $T_1$ to a certain $g$ factor. This becomes a problem when several electronic states with different $g$ factors are present in the system, e.g. electrons and holes. We solve this problem by optically pumping spin polarization and then selectively depolarizing it using a radio frequency (rf) field. By modulating the rf field one can observe the retarded modulation of spin polarization which depends on the relation between the modulation period and $T_1$. Using this selective spin inertia method, we unveil the strong anisotropy of $T_1$ for rare-earth Ce$^{3+}$ ions in a YAG crystal at low temperatures and low magnetic fields. We also show that the spread of Larmor frequencies within the electron ensemble in this system is not static, but results from the fluctuations of internal magnetic fields on a timescale much shorter than $T_1$.

Spin Laser Local Oscillators for Homodyne Detection in Coherent Optical Communications.

We numerically investigate spin-controlled vertical-cavity surface-emitting lasers (spin-VCSELs) for local oscillators, which are based on an injection locking technique used in coherent optical communications. Under the spin polarization modulation of an injection-locked spin-VCSEL, frequency-shifted and phase-correlated optical sidebands are generated with an orthogonal polarization against the injection light, and one of the sidebands is resonantly enhanced due to the linear birefringence in the spin-VCSEL. We determine that the peak strength and peak frequency in the spin polarization modulation sensitivity of the injection-locked spin-VCSEL depend on detuning frequency and injection ratio conditions. As a proof of concept, 25-Gbaud and 16-ary quadrature amplitude modulation optical data signals and a pilot tone are generated, and the pilot tone is used for the injection locking of a spin-VCSEL. An orthogonally-polarized modulation sideband generated from the injection-locked spin-VCSEL is used as a frequency-shifted local oscillator (LO). We verify that the frequency-shifted LO can be used for the homodyne detection of optical data signals with no degradation. Our findings suggest a novel application of spin-VCSELs for coherent optical communications.

Spin polarization modulation for high-speed vertical-cavity surface-emitting lasers

The spin polarization modulation in birefringent vertical-cavity surface-emitting lasers (VCSELs) is investigated theoretically and experimentally for obtaining tailored polarization modulation characteristics suitable for high-speed data communications. A spin-flip rate equation analysis reveals that the spin polarization modulation response of VCSELs is flattened by shortening the electron spin relaxation time and its 3-dB bandwidth is broadened to a range determined by a frequency split between two orthogonal polarization modes. Optical modulations of spin polarized electrons in commercially-available InAlGaAs quantum well VCSELs demonstrate a wide 3-dB bandwidth of 23 GHz determined by the frequency split, which indicates that the spin relaxation time in the InAlGaAs quantum well VCSEL is around 20 ps at room temperature and suitable for use in high-speed data communications at a telecom wavelength of 1.55 μm.

Modulation of spatial spin polarization at organic spinterface by side groups

Abstract Spin polarization at benzene/Ni organic/ferromagnetic interface is investigated by applying different substituting side groups. Based on first-principle calculations, it is demonstrated that the spin polarization of the states may be tuned in magnitude and sign by the side groups, which depends on the type of side groups as well as their position in the aromatic ring. Especially, a spatial spin polarization modulation is realized at the surface with the utilization of electron donating group NH 2 or electron accepting group NO 2. The analysis of projected density of states onto the p z orbital of carbon atoms indicates that the side group reduces the structural symmetry of the molecule and changes the p z orbital of carbon atom at different position, which further modifies the p z - d orbital hybridization as well as the spin transfer between the molecule and the ferromagnet. This work indicates a feasible way to modulate the spatial spin polarization at organic spinterface by side groups, which deserves to be measured by spin-polarized scanning tunneling microscopy.

Antiferromagnetic order in CeCoIn5oriented by spin-orbital coupling

An incommensurate spin-density wave (Q phase) confined inside the superconducting state at high basal plane magnetic field is an unique property of the heavy-fermion metal CeCoIn5. The neutron scattering experiments and the theoretical studies point out that this state come out from the soft mode condensation of magnetic resonance excitations. We show that the fixation of direction of antiferromagnetic modulations by a magnetic field reported by Gerber et al. [Nat. Phys. 10, 126 (2014)], is explained by spin-orbit coupling. This result, obtained on the basis of quite general phenomenological arguments, is supported by the microscopic derivation of the χ z z susceptibility dependence on the mutual orientation of the basal plane magnetic field and the direction of modulation of spin polarization in a multiband metal.

Spin filtering magnetic modulation and spin-polarization switching in hybrid ferromagnet/semiconductor structures

Electron spin-polarization modulation with a ferromagnetic strip of in-plane magnetization is analyzed in a hybrid ferromagnet/semiconductor filter device. The dependencies of electron spin-polarization on the strip’s magnetization strength, width and position have been systematically investigated. A novel magnetic control spin-polarization switch is proposed by inserting a ferromagnetic metal (FM) strip eccentric in relation to off the center of the spin filter, which produces the first energy level spin-polarization reversal. It is believed to be of significant importance for the realization of semiconductor spintronics multiplevalue logic devices.

Magnetocurrent of Charge-Polarizable C60-Diphenylaminofluorene Monoadduct-Derived Magnetic Nanocomposites

We demonstrated the strategy of a nanocomposite design by the incorporation of both a delocalized π-electrons system in a closely bound acceptor-donor analogue chromophore, based on charge-polarizable C(60)(>DPAF-C(9)) nanostructure 1, and spin-polarized d-electrons in the form of γ-FeO(x) nanoparticles. Facile intramolecular electron transfer from the DPAF-C(9) donor moiety to the C(60) acceptor cage of 1 upon activation to the excited state with a long lifetime of the charge-separated state forms a possible mechanism to integrate semiconducting and magnetic properties in a single system. We observed an appreciable magnetocurrent (MC) of C(60)(>DPAF-C(9))-encapsulated magnetic γ-FeO(x) nanoparticles in PMMA matrix upon applying a magnetic field from 0 to 300 mT at either 77 K (12% MC) or 300 K (4.5% MC). Interestingly, the detailed analysis of magnetocurrent curve profiles taken at 77 K allowed us to conclude that the measured magnetocurrent may be attributed to the contributions from magnetic field-dependent excited-state populations in semiconducting structure (density-based MC), magnetism from magnetic structure (mobility-based MC), and product of density and mobility-based MC components (π-d electronic coupling). At the higher temperature region up to 300 K, the semiconducting mechanism dominated the determining factor of measured magnetocurrent. This experimental observation indicated the feasibility of combining delocalized π electrons and spin-polarized d electrons through charge transfer to induce internally coupled dual mobility- and density-based MC through the modulation of spin polarization and excited states in semiconducting/magnetic hybrid materials.

Spatial Modulation of Spin Polarization within a Single Co Island

When electrons are confined to nanostructures, quantum interference takes place due to their wave-particle duality. Using spin-polarized scanning tunneling microscopy, we studied the influence of quantum interference of electrons on the spatial distribution of the spin polarization within a single magnetic nanostructure. We find changes in both the magnitude and sign of the spin polarization on a subnanometer scale. We compare our experimental results with ab initio calculations of the spin-resolved local density of states (LDOS). We find that the modulation of the spin-polarization at a given energy can be ascribed to the different magnitudes of spatially modulated majority states and non-modulated minority states contributing to the total LDOS.