SPIN

A theoretical formalism for calculating the bulk and surface spin modes in Heisenberg semi-infinite lattices is presented on a ferromagnetic cubic network of spins, coupled via nearest and next-nearest neighbors exchange interactions. The magnetic surface can be considered as semi-infinite slabs at the end of the bulk structures. The breakdown of translation symmetry, in the normal direction of the surface, gives rise to localized spin wave modes in its neighborhood. The localized magnon spectrum is derived as elements of a Landauer-type scattering matrix, in the three cubic lattices sc, bcc and fcc. The magnon properties are simulated and determined numerically for each cubic lattice by using the matching technique. The observed fluctuations in the numerical results demonstrate the interference magnon effects between scattered spinwaves and the localized magnon states, generated by the surface region with characteristic Fano resonances. In cubic leads, the localized surface spin states are sensitive to the local magnetic coupling and the incident direction in the surface boundary. In this contribution, the normalized energy of spinwaves arising from the absence of translation symmetry is analyzed for each cubic system as a function of the exchange integral parameters. This addresses the dependence of the surface magnon on the different possibilities of the of the exchange parameters variation from softening to hardening in the neighborhood of the surface region.

Graph computation is a core technique for solving realistic problems of graph representations. In solving the shortest path problem (SPP), the current classical methods are encountering a huge performance bottleneck. Attempting to solve this dilemma, we try to solve the SPP with a Quantum Approximate Optimal Algorithm (QAOA)-based quantum method. In this paper, we propose a QAOA-based shortest path algorithm (SPA) by constructing a suitable Hamiltonian quantity and using the idea of variational quantum computing, and verify the algorithm using a quantum simulator and an International Business Machines cloud quantum computer. The proposed algorithm is able to achieve a near-optimal solution with a correct rate that significantly exceeds the invalid solutions, reaching a good preliminary result. Furthermore, the proposed algorithm is expected to achieve a huge advantage over the classical algorithm and the SPA based on Grover’s algorithm with a suitable selection of parameters and number of steps. In addition, the proposed algorithm requires fewer quantum bits than other quantum algorithms, thus promising quantum computing superiority on current noisy intermediate-scale quantum (NISQ) quantum computing devices.

In this paper, we investigate the synchronization phenomenon between two Spin-transfer Torque Nanooscillators (STNOs) of different frequencies in two pillar systems under vortex configuration detunings or driving frequencies. The oscillators’ mutual synchronization occurs through magnetic dipolar interaction. Our micromagnetic simulations show that an amplitude fluctuation referred to as ${\mathrm{\Gamma }}_p$ has a significant impact on determining the synchronization frequency. The evolution of frequency and amplitude fluctuation rate in two different oscillator sizes versus external perpendicular field will be compared and discussed. Our results reveal that the oscillator with lower ${\mathrm{\Gamma }}_p$, referred to as the “Leader” oscillator, leads the synchronization process. As such, the “follower” oscillator adjusts its frequency as to that of the “Leader”, thus achieving synchronization. We believe that taking ${\mathrm{\Gamma }}_p$ into consideration can help in controlling synchronization frequencies in future building blocks of any network multi-array spintronics’ devices.

In the present investigation, the synthesis of the strontium copper titanate $({\mathrm{\text{Sr}}}_3{\mathrm{\text{CuTi}}}_4{\mathrm{\text{O}}}_{12},\mathrm{\text{SCTO}})$ ceramic by the cost-effective solid-state reaction was reported. The structural analysis suggests a single-phase tetragonal crystal symmetry with space group P4/mmm. The average crystallite size and mechanical compressive microlattice strain are found to be 65.8nm and 0.000594, respectively. The study of the field emission scanning electron microscope (FESEM) micrograph suggests that grains and grain boundaries are uniformly distributed on the sample surface with less porosity. The study of Raman lines suggests the presence of all constituent elements, which is well supported by EDAX analysis. The UV–Vis spectroscopy analysis shows that the bandgap of SCTO is about 3.2eV suitable for photovoltaic and other higher-temperature sensor applications. The decrease of dielectric constant with frequency supports the reduction of space charge polarization. The modulus analysis suggests that the immobile charge carriers at lower and defects and oxygen vacancies at higher temperatures are responsible for the thermally activated conduction process. The calculated activation energies are 4.54meV, 4.40meV, 3.39meV and 3.29meV at 1kHz, 10kHz, 100kHz and 1MHz; the decrease with the rise of the frequency confirms a thermally activated conduction process. Thermistor constant $(\beta )$, sensitivity factor $(\alpha )$ and stability factor of the sample were calculated, which confirms the characteristics of the NTC thermistor. The Nyquist and Cole–Cole semicircular arcs confirm NTCR character and are found to be suitable applications for energy storage devices and thermistors.

By using a Monte Carlo simulation, we have studied the effects on the multilayer transition and magnetic properties of the crystal field $D∕J_2$, the four-spin coupling $J_4∕J_2$ and RKKY interaction in the spin-1 Ashkin–Teller (AT) model of a system composed of two magnetic multi-layer materials, of various thicknesses, separated by a nonmagnetic spacer of thickness $M$. By varying the strength of $J_4∕J_2$, we have obtained a new partially ordered phase $〈\sigma S〉$, for different values of $D∕J_2$. We have established a rich phase diagram with first and second-order phase transitions with tricritical points. It is shown that the transition temperature of both magnetic blocks depends strongly on the thickness of the magnetic layers $N$, as well as $J_4∕J_2$ and $D∕J_2$. There exists a critical thickness of the magnetic layers $N_L$ above which the multilayer blocks undergo a transition separately at different temperatures, for a high value of $J_4∕J_2$ and $D∕J_2$. Besides, the critical exponents are computed.

In this paper, we report the first theoretical results on the acoustic generation of spin accumulation in ferromagnet-semiconductor-ferromagnet trilayers. As a representative material system, we consider a Ni/GaAs/Ni trilayer coupled to a piezoelectric transducer, which injects a planar acoustic wave into the adjoining Ni film. By combining an analytical solution of the spin diffusion equation in the GaAs spacer with results of numerical simulations of the coupled elastic and magnetic dynamics in the Ni films, we quantify an oscillating inhomogeneous spin accumulation in GaAs. It is found that both dc and ac parts of the mean spin accumulation vary nonmonotonically with the spacer thickness $t_{\mathrm{\text{S}}}$, reaching maximal values at $t_{\mathrm{\text{S}}}$ mostly close to 0.25 or 0.75 of the wavelength of the injected monochromatic acoustic wave. Remarkably, the transverse wave generates the spin accumulation much more efficiently than the longitudinal one. Our theoretical predictions provide guidelines for the development and optimization of energy-efficient acoustic spin injectors into semiconductors, which should have much lower power consumption than injectors driven by the microwave magnetic field.

One avenue toward next-generation spintronic devices is to develop half-metallic ferromagnets with 100% spin polarization and Curie temperature above room temperature. Half-metallic ferromagnets have unique density of states, where the majority spins are metallic but the minority spins are semiconducting with the Fermi level lying within an energy gap. To date, the half-metallic bandgap has been predominantly estimated using Jullière’s formula in a magnetic tunnel junction or measured by the Andreev reflection at low temperature, both of which are very sensitive to the surface/interface spin polarization. Alternative optical methods such as photoemission have also been employed but with a complicated and expensive setup. In this study, we developed and optimized a new technique to directly measure the half-metallic bandgap by introducing circularly polarized infrared light to excite minority spins. The absorption of the light represents the bandgap under a magnetic field to saturate the magnetization of a sample. This technique can be used to provide simple evaluation of a half-metallic film.

The spin injection efficiency in the Ferromagnetic/Nonmagnetic Semiconductor/Ferromagnetic (FM/NMS/FM) structures was studied under external magnetic and electric fields. It is found that spin injection efficiency can be strongly influenced by magnetic and electric fields. With the increase of these fields, the down-stream spin diffusion length increases and makes the spin injection efficiency increase. Furthermore, the effects of many-body correlations and exchange reduces the value of the diffusion constant that leads to enhance spin injection efficiency.

In this work, we model the salient magnetic properties of the alloy lamellar ferrimagnetic nanostructures ${[{\mathrm{\text{Co}}}_{1-c}{\mathrm{\text{Gd}}}_c]}_{{\ell }^{\prime }}{[\mathrm{\text{Co}}]}_{\ell }{[{\mathrm{\text{Co}}}_{1-c}{\mathrm{\text{Gd}}}_c]}_{{\ell }^{\prime }}$ between $\mathrm{\text{Co}}$ semiinfinite leads. We have employed the Ising spin effective field theory (EFT) to compute the reliable magnetic exchange constants for the pure cobalt $J_{\mathrm{\text{Co–Co}}}$ and gadolinium $J_{\mathrm{\text{Gd–Gd}}}$ materials in complete agreement with their experimental data. The sublattice magnetizations of the $\mathrm{\text{Co}}$ and $\mathrm{\text{Gd}}$ sites on the individual hcp atomic (0001) planes of the Co–Gd layered nanostructures are computed for each plane and corresponding sites by using the combined EFT and mean field theory (MFT) spin methods. The sublattice magnetizations, effective site magnetic moments, and ferrimagnetic compensation characteristics for the individual hcp atomic planes of the embedded nanostructures, are computed as a function of temperature, and for various stable eutectic concentrations in the range $c\le 0.5$. The theoretical results for the sublattice magnetizations and the local magnetic variables of these ultrathin ferrimagnetic lamellar nanostructured systems, between cobalt leads, are necessary for the study of their magnonic transport properties, and eventually their spintronic dynamic computations. The method developed in this work is general and can be applied to comparable magnetic systems nanostructured with other materials.

An experimental approach to the problem of the energy distribution of radiation in the THz range created by an electron flow passing through a magnetic junction between thermal and dynamic is considered. The experimental results obtained during the operation of a spin-injection emitter based on an array of heterogeneous magnetic nanowires (NWs) confirmed the assumption about the “competition” of thermal and dynamic radiation processes.