SPIN

Structural, elastic, electronic and magnetic properties of Ru₂Co$Z$ ($Z=\mathrm{\text{Si}}$, Ge and Sn) alloys are investigated by using potentially linearized augmented plane-wave method based on the framework of spin density functional theory. The exchange correlation potential is treated by the generalized gradient approximation of Perdew, Burke and Ernzerhof (GGA-PBE) and the modified Becke–Johnson potential mBJ-GGA-PBE form. The calculated lattice parameters, local magnetic moment and heat of formation have been calculated. The elastic constants, $C_{ij}$, and other polycrystalline elastic moduli have been predicted, and the mechanical stabilities of these alloys have been theoretically confirmed. To our knowledge, the elastic constants have not yet been measured or calculated; hence, our results serve as a prediction for future study. Also, we presented results of the band structure and density of states. The electronic structure in the ferromagnetic configuration shows metallic character and that there is an exchange splitting between spin-up and spin-down bands of Ru 4d and Co3d states.

The critical behavior at the phase transition of the ferromagnetic two-dimensional anisotropic Ising model with next-nearest neighbor (NNN) couplings in the presence of the field is determined using mainly Monte Carlo (MC) method. This method is used to investigate the phase diagram of the model and to verify the existence of a divergence at null temperature which often appears in two-dimensional systems. We analyze also the influence of the report of the NNN interactions $J_d∕J_h$ and the magnetic field $h$ on the critical temperature of the system, and we show that the critical temperature depends on the magnetic field for positive values of the interaction. Finally, we have investigated other thermodynamical qualities such as the magnetic susceptibility $\chi$. It has been shown that their thermal behavior depends qualitatively and quantitatively on the strength of NNN interactions and the magnetic field.

The electronic structure and magnetic stability of substitutional rare-earth (Er) impurities in InGaN are calculated using the full potential linearized augmented plane wave (FP-LAPW) method with local density approximation functional (LSDA$+$U). The calculation of formation energy shows that it is more energetically favorable for a substitutional rare earth (Er) atom to replace the In atom than the Ga atom. A semiconductor behavior with a direct band gap is predicted for the concentration InGaN:Er, which is the favored semiconductor when fabricating light emitting devices, with magnetic moment of 3.02 ${\mu }_B$. The top of the valence band is formed predominantly with hybridized $d$-states of Er and $p$-states of N, while the bottom of the conduction band is formed by the hybrid Ga-s/Ga-p states with a small contribution of N-s states. Our calculations reveal that the coupling between rare earth-impurity atoms is ferromagnetic. We discuss the bands, total and partial densities of states.

Using atomistic Monte Carlo simulations, we investigated the impact of the interface on the structural properties of iron and copper (Fe/Cu) magnetic multilayers grown by Voronoi diagram. Interest in magnetic multilayers has recently emerged as they are shown to be promising candidates for magnetic storage media, magneto-resistive sensors and personalized medical treatment. As these artificial materials show large differences in properties compared to conventional ones, many experimental and theoretical works have been dedicated on shedding light on these differences and tremendous results have emerged. However, little is known about the influence of the interfaces on magnetic layers. Using numerical approaches, we show that the structure of each layer depends on its thickness and the interface morphology. The Fe and Cu layers can adopt either the body-centered-cubic (bcc) or face-centered-cubic (fcc) structure, while the interface can assume amorphous, bcc, fcc, or a mixture of bcc and fcc structures depending on the layer thicknesses. These results are in good agreement with the experiments. They could be helpful in understanding effects such as giant magneto-resistance from the structural perspective.

Synchronization of spin-torque nano-oscillators (STNOs) by magnetic dipolar interactions in a parallel electrical connection (PC) introduces the technological possibility for an enhancement of output signal. In this study, we consider two identical or nonidentical STNOs in serial electrical connection (SC). By using a pendulum-like approximation model, we analytically predict the dipolar coupling strength, critical current and frequency of phase-locking precession. The numerical calculations of those analytical expressions are confirmed by macrospin simulations, revealing that the dipolar coupling strength responsible for the phase-locking in SC case is three times larger than that in the PC case for the two STNOs with the same separation, which results in the enlarged and symmetric phase-locking window of frequency versus current. These results suggest that the SC of multiple STNOs could be more promising for the enhancement of output power.

Laser-induced magnetization switching in GdFe ferrimagnets strongly depends on the pulse duration. To gain insight into the ferrimagnetic switching process, Landau–Lifshitz–Gilbert (LLG) spin dynamic modeling is performed at an atomistic-level with two sub-lattice systems. The switching dynamics triggered by laser pulses can be considered as two stages: Demagnetization stage by the laser pulse heating and re-magnetization at the cooling down stage after the pulse impulsion. By tuning the laser pulse duration, the intensity of demagnetization can be well controlled, by which the subsequent magnetization switching during the cooling process can be obtained. The simulation results indicate that the occurrence of the transient ferromagnetic-like (TFL) state is necessary during the magnetization switching process. Furthermore, the thermal temperature and heating time play an important role for the ferrimagnetic switching. In the overheating region, the random switching behavior appears because the TFL state is uncontrollable.