Spectral properties of terahertz radiation from laterally structured spintronic emitters

In this work, the spectral properties of the terahertz radiation of a spintronic emitter based on the Co(2 nm)/Pt(2 nm) ferromagnet/heavy metal heterostructure and the periodic system of strips made of it (period from 4 μm to 1 mm) have been experimentally studied. Two main mechanisms that determine the terahertz spectrum of such emitters are demonstrated. The first of them is observed both in a continuous multilayer film and in a periodic lattice. In this mechanism, due to the interference of signals from different spatial regions of the emitter, the amplitude of the wave decreases with an increase in the angle between the normal to the film and the direction of radiation propagation, and the characteristic scale of this decrease depends on the wavelength. As a result, the increase in this angle is accompanied by the redshift of the spectral amplitude maximum of radiation. The second mechanism is possible only in the periodic system of strips. It occurs as the fact suppression of terahertz radiation due to the charge accumulation at the boundaries of the strips when periodic lattices with a short period are magnetized along the strips. This effect is more significant for longer wavelengths and is therefore accompanied by a blueshift of the spectral maximum. The mechanisms studied in this work will make it possible to create spintronic emitters of terahertz radiation with a given position of the spectral amplitude maximum of terahertz radiation.