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.

Giant magnetostriction (GMS) reported until now in exchange-coupled multilayers (ECML) present quasi-isotropic magnetostrictive behavior. In the present work it is shown the possibility to induce highly anisotropic GMS at low field with the single domain state in (TbFe/Fe)n multilayers when deposited by ion sputtering under a magnetic polarization field Hd. ECML grown under bias field Hd, applied along the large size of rectangular glass substrates present original magnetic and magnetoelastic (ME) properties associated with strong uniaxial behavior. After saturation by an external field H∥ applied parallel to the easy axis induced by Hd, a single domain state is kept by decreasing H∥ down to zero (Mr/Ms=1) which explains why there is no change of the magnetoelastic coefficient bγ,2 by increasing or decreasing H∥. A different behavior arises along the hard magnetization axis with a strong change of bγ,2 by increasing H∥ up to the saturation. ME anisotropy is the origin of high amplitude flexural and torsional oscillation modes as observed in our ECML.

We report an increase in terahertz (THz) radiation efficiency due to FeCo/WSe2 structures in the reflection geometry. This can be attributed to an absorption increase in the alloy FeCo layer at the input FeCo/WSe2 interface due to constructive interference, as well as to the backward transport of hot carriers from FeCo to WSe2. In contrast to the transmission geometry, the THz generation efficiency in the reflection is much less dependent on the magnetic layer thickness. Our results suggest a cheap and efficient way to improve the characteristics of THz spintronic emitters with the conservation of a full set of their important properties.

Intermetallic heterostructures of rare-earth and transition metals exhibit physical properties prospective for various applications. These structures combine giant magnetostriction, controllable magnetic anisotropy, magneto-optical activity and allow spin reorientation transitions (SRT) induced by magnetic field at room temperature. Here, we present the results of a study of spin dynamics induced by ultrafast optical excitation in the $$\hbox {TbCo}_2\hbox {/FeCo}$$ TbCo 2 /FeCo heterostructure. The time dependence of the light polarization rotation excited by a pump optical pulse with a duration of 35 fs was measured in the total range of the SRT created by external DC magnetic field. We found hysteretic dependence of the polarization rotation on magnetizing field that is specific for spin dynamics near SRT. Enhancement of the rotation is observed in the critical points of the SRT and near the points of magnetization switch from metastable to stable spin states. In the time-domain, two characteristic delays of 20 ps and 200 ps were found, corresponding to the maximum deviation of the light polarization after excitation. The first is explained by the precession motion of spins out of the plane of the structure. The latter is accounted for the spin in-plane deviation from its initial position and thermal relaxation of the anisotropy.