Steering magnonic dynamics and permeability at exceptional points in a parity–time symmetric waveguide

Tuning the magneto optical response and magnetic dynamics are key elements in designing magnetic metamaterials and devices. This theoretical study uncovers a highly effective way of controlling the magnetic permeability via shaping the magnonic properties of coupled magnetic waveguides separated by a nonmagnetic spacer with strong spin–orbit interaction (SOI). We demonstrate how a spacer charge current leads to enhancement of magnetic damping in one waveguide and a decrease in the other, constituting a bias-controlled magnetic parity–time (PT) symmetric system at the verge of the exceptional point where magnetic gains/losses are balanced. We find phenomena inherent to PT-symmetric systems and SOI-driven interfacial structures, including field-controlled magnon power oscillations, nonreciprocal propagation, magnon trapping and enhancement as well as an increased sensitivity to perturbations and abrupt spin reversal. The results point to a new route for designing magnonic waveguides and microstructures with enhanced magnetic response.

Enhancing Frequency and Reducing the Power of Spin-Torque Nanooscillator By The Generated Oersted Field

The current-driven magnetization precession dynamics stimulated by Spin-Transfer Torque (STT) in a trilayer spin-valve device (typically Spin-Torque Nanooscillator (STNO)) is numerically investigated by solving the Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. We have devised four STNO devices made of ferromagnetic alloys such as CoPt, CoFeB, Fe[Formula: see text]B[Formula: see text]Ni2 and EuO, which act as free and fixed layers. Here, copper acts as a nonmagnetic spacer for all the devices. In this work, we have introduced the current-induced Oersted field, which is generated when a spin-polarized current passes through the device. The generated Oersted field strength is varied by increasing the diameter of the STNO device. Frequency tunability is achieved in all the four devices, whereas the power of the individual device reduces. The frequency and power of the devices depend entirely on the saturation magnetization of the material, which inherently reflects in the current density and the coherence of the spin-polarized DC. In all devices, the frequency increases, whereas the power decreases by increasing the strength of the Oersted field. Among the four devices, the maximum frequency can be tuned up to 104[Formula: see text]GHz with 40[Formula: see text]nm device diameter, which is obtained for EuO material. This opens a promising source and paves a glittering future for the nanoscale spintronic devices.

Influence of the Thickness of Nonmagnetic Spacer on the Magnetic Properties of Fe/Cu Multilayered Nanowires

We present a systematic investigation on the equilibrium structure, stability and magnetic properties of one-dimensional Fe/Cu multilayered nanowires with different width of nonmagnetic Cu spacer using first-principles calculations. The multilayered nanowires preserve their FCC (001) directional lattice symmetry after structural optimization. It is found that the stability of Fe/Cu multilayered nanowires decreases with increasing concentration of nonmagnetic Cu layers. The calculated interlayer exchange coupling (IEC) is found to switch signs as the thickness of nonmagnetic Cu spacer increases in the nanowire, and the magnitude of the IEC value is found to decrease significantly with increasing the number of nonmagnetic Cu layers.

Numerical simulation of spin transport in systems with complex geometry

The spin diffusion and charge equations in Levy-Fert and Waintal models were numerically solved, using finite element method in complex non-collinear geometry with strongly inhomogeneous current flow. As an illustration, spin-dependent transport through a magnetic pillar and nonmagnetic spacer separating two magnetic layers was investigated. It is shown, that the structure with number of pillars gives a higher value of Giant Magnetoresistance (GMR) effect rather than a structure with one pillar of equivalent diameter. The inhomogeneity of spin currents, which has one of the strongest impacts on GMR effect value leads to the occurrence of spin-current vortices. Introduction of lT and lL lengths in Waintal model gives a better description of angular dependence of GMR effect rather than Levy-Fert model.