A micromagnetic and elastodynamic finite element model is used to compare the 180° out-of-plane magnetic switching behavior of CoFeB and Terfenol-D nanodots with perpendicular magnetic easy axes. The systems simulated here consist of 50 nm diameter nanodots on top of a 100 nm-thick PZT (Pby[ZrxTi1-x]O3) thin film, which is attached to a Si substrate. This allows voltage pulses to induce strain-mediated magnetic switching in a magnetic field free environment. Coherent and incoherent switching behaviors are observed in both CoFeB and Terfenol nanodots, with incoherent flipping associated with larger or faster applied switching voltages. The energy to flip a Terfenol-D memory element is an ultralow 22 aJ, which is 3–4 orders more efficient than spin-transfer-torque. Consecutive switching is also demonstrated by applying sequential 2.8 V voltage pulses to a CoFeB nanodot system with switching times as low as 0.2 ns.

We simulated the generation and propagation of spin waves (SWs) using two excitation methods, namely, magnetic field and voltage induced strain. A fully coupled non-linear magnetoelastic model, combining Landau–Lifshitz-Gilbert with elastodynamic equations, is used to study the propagation characteristics of SWs in magnetoelastic materials. Simulation results show that for excitation frequencies above ferromagnetic resonance (FMR), SWs excited by voltage induced strain propagate over longer distances compared to SWs excited by magnetic field. In addition, strain mediated SWs exhibit loss characteristics, which are relatively independent of the magnetic losses (Gilbert damping). Moreover, it is also shown that strain induced SWs can also be excited at frequencies below FMR.

We describe a spin wave modulator – spintronic device aimed to control spin wave propagation by an electric field. The modulator consists of a ferromagnetic film serving as a spin wave bus combined with a synthetic multiferroic comprising piezoelectric and magnetostrictive materials. Its operation is based on the stress-mediated coupling between the piezoelectric and magnetostrictive materials. By applying an electric field to the piezoelectric layer, the stress is produced. In turn, the stress changes the direction of the easy axis in the magnetostrictive layer and affects spin wave transport. We present experimental data on a prototype consisting of a piezoelectric [Pb(Mg1/3Nb2/3)O3](1-x) –[PbTiO3]x substrate, and 30 nm layer of magnetostrictive Ni film, where the film is attached to a 30 nm thick Ni81Fe19 spin wave bus. We report spin wave signal modulation in Ni81Fe19 layer by an electric field applied across the piezoelectric layer. The switching between the spin wave conducting and non-conducting states is achieved by applying ±0.3 MV/m electric field. We report over 300% modulation depth detected 80 μm away from the excitation port at room temperature. The demonstration of the spin wave modulator provides a new direction for spin-based device development by utilizing an electric field for spin current control.

Spin waves are of great interest as an emerging solution for computing beyond the limitations of scaled transistor technology. In such applications, the frequency of the spin waves is important as it affects the overall frequency performance of the resulting devices. In conventional ferromagnetic thin films, the magnetization dynamics in ferromagnetic resonance (FMR) and spin-waves are limited by the saturation magnetization of the ferromagnetic (FM) material and the external bias field. High-frequency applications would require high external magnetic fields which limit the practicality in a realistic device. One solution is to couple microwave excitations to perpendicular standing spin-waves (PSSWs) which can enable higher oscillation frequencies. However, efficient coupling to these modes remains a challenge since it requires an excitation that is non-uniform across the FM material thickness and current methods have proven to be inefficient, resulting in weak excitations. Here, we show that by creating periodic undulations in a 100 nm thick Co 40 Fe 40 B 20 layer, high-frequency PSSWs (>20 GHz) can be efficiently excited using micrometer sized transducers at bias fields below 100 Oe which absorb nearly 10% of the input RF power. Efficient excitation of such spin-waves at low fields may enable high

Using the plane wave method, we study two two-dimensional structures that possess absolute photonic band gaps: the triangular and the graphite photonic crystals. We compare their convenience in achieving photonic crystals which inhibit the propagation of visible electromagnetic waves. We show that this is very difficult to obtain with a triangular structure because its gap is too narrow and its dimensions are too small to be fabricated. On the contrary, wider gaps and larger dimensions that can easily be etched makes graphite a much more appropriate structure.