Polarization control of THz emission using spin-reorientation transition in spintronic heterostructure

Abstract

Polarization of electromagnetic waves plays an extremely important role in interaction of radiation with matter. In particular, interaction of polarized waves with ordered matter strongly depends on orientation and symmetry of vibrations of chemical bonds in crystals. In quantum technologies, the polarization of photons is considered as a “degree of freedom”, which is one of the main parameters that ensure efficient quantum computing. However, even for visible light, polarization control is in most cases separated from light emission. In this paper, we report on a new type of polarization control, implemented directly in a spintronic terahertz emitter. The principle of control, realized by a weak magnetic field at room temperature, is based on a spin-reorientation transition (SRT) in an intermetallic heterostructure TbCo2/FeCo with uniaxial in-plane magnetic anisotropy. SRT is implemented under magnetic field of variable strength but of a fixed direction, orthogonal to the easy magnetization axis. Variation of the magnetic field strength in the angular (canted) phase of the SRT causes magnetization rotation without changing its magnitude. The charge current excited by the spin-to-charge conversion is orthogonal to the magnetization. As a result, THz polarization rotates synchronously with magnetization when magnetic field strength changes. Importantly, the radiation intensity does not change in this case. Control of polarization by SRT is applicable regardless of the spintronic mechanism of the THz emission, provided that the polarization direction is determined by the magnetic moment orientation. The results obtained open the prospect for the development of the SRT approach for THz emission control.

Composite Multiferroic Terahertz Emitter: Polarization Control via an Electric Field

“…1(c)]. In the THz TbCo2/Fe-Co emitter, a change in the absolute value of the magnetic field below the anisotropy field, HA, rotates polarization [40]. When all optical components are fixed, the Zn-Te-based detection system acts as an optical analyzer measuring the Ey-THz-field component [44][45][46].…”

“…Initially, the idea of mechanical rotation of a magnet around the emitter was proposed [39]. Then an emitter was developed that rotated the polarization by simply increasingdecreasing the current in the electromagnet [40]; the operation is based on a spin-reorientation phase transition in magnetic nanostructures. In Ref.…”

“…To integrate the spintronic principle of emission with the multiferroic concept of controlling the magnetization by an electric field, we use a high-quality magnetostrictive superlattice deposited on an anisotropic piezoelectric substrate, while the THz wave is generated in the superlattice by an optical femtosecond pulse. The principle of polarization control in such a structure is based on the strain-mediated coupling of magnetic and piezoelectric subsystems in the range of the spin-reorientation transition [17,18,40]. By comparison of the experimental results with the theoretical model, we determine the parameter of magnetoelectrically induced anisotropy, which is responsible for the rotation of the magnetization and THz polarization.…”

Increasing the Efficiency of a Spintronic THz Emitter Based on WSe2/FeCo

“…Then, the peak-to-peak values of the THz signal, proportional to the instantaneous value of the electric field in the THz pulse, were measured using the software processing of the time domain dependences. Rotating the WGP allows one to determine the polarization of THz radiation (for details, see [2]).…”

“…Among the many different types of terahertz (THz) emitters using various physical effects, spintronic ones demonstrate many noticeable advantages, primarily ultra-broad bandwidth but also a high efficiency and ease of control of radiation parameters: polarization [1][2][3][4], amplitude [5,6], phase [7]. Benefits such as an ease of integration and low cost allow spintronic emitters to be integrated into a variety of end-user devices for spectroscopy, medicine and safety.…”