Sulymenko O. Synchronization and generation of electromagnetic signals in spintronic magnetic nanostructures.

This work is devoted to the theoretical analysis of microwave synchronization and terahertz-frequency generation of electromagnetic signals in spintronic magnetic nanostructures (SMNS) and devices that utilize SMNS by numerical computing. The numerical model of the mutual synchronization of an arbitrary number of weakly coupled STNOs taking into account the technological spread of STNO’s parameters was presented. The use of this model for the case of two, three, five, ten, and twenty STNOs having various technological spreads of the oscillators’ parameters was demonstrated. The study of the STNO-array geometry effect on the efficiency of synchronization was carried out using the approach of a “local coupling”. For the first time, it was shown that for two-dimensional arrays, exist an optimal distance between the nearest STNOs, for which synchronization is most effective, and this distance essentially depends on the topology of the system. The new concept of a terahertz-frequency signal oscillator was proposed. Such oscillator is layered structure that consist of a current-driven platinum (Pt) layer and an antiferromagnetic (AFM) layer. The AFM layer has an easy-plane anisotropy and its sublattices are canted inside the easy plane by the Dzyaloshinskii-Moriya interaction (DMI). The dc electric current flowing in the Pt layer creates a perpendicular spin current due to the spin Hall effect. This spin current being injected in the AFM layer, tilts the DMI-canted AFM sublattices out of the easy plane, thus exposing them to the action of a strong internal exchange magnetic field of the AFM. The sublattice magnetizations, along with the small net magnetization of the canted AFM, start to rotate about the hard anisotropy axis of the AFM with the terahertz frequency proportional to the injected spin current and the AFM exchange field. The rotation of the small net magnetization results in the terahertz-frequency dipolar radiation that can be directly received by an adjacent (e.g., dielectric) resonator. It was demonstrated theoretically that the radiation in the frequency band f ~0,05–2 THz are possible at the experimentally reachable magnitudes of the driving current density, and we evaluate the power of the signal radiated into different types of resonators. This power increases with the increase of frequency f, and it can exceed 1 μW at f ∼ 0,5 THz using a typical dielectric resonator with the electric permittivity ε ∼ 10 and a quality factor Q ∼ 750.