The interaction of a single-cycle terahertz electric field with the topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ triggers strongly anharmonic lattice dynamics, promoting fully coherent energy transfer between the otherwise noninteracting Raman-active $E_g$ and infrared (IR)-active $E_u$ phononic modes. Two-dimensional terahertz spectroscopy combined with modeling based on the classical equations of motion and symmetry analysis reveals the multistage process underlying the excitation of the Raman-active $E_g$ phonon. In this nonlinear combined photophononic process, the terahertz electric field first prepares a coherent IR-active $E_u$ phononic state and subsequently interacts with this state to efficiently excite the $E_g$ phonon.

Experimental studies of the anomalous Hall effect are performed for thin-film $\mathrm{Ta}/\mathrm{Tb}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$ over a wide range of temperatures and magnetic fields up to 3 T. Far from the compensation temperature ($T_{M}$ = 277 K), the field dependence has a conventional shape of a single hysteresis loop; just below the compensation point, the dependence is anomalous with the shape of a triple hysteresis. To understand this behavior, we experimentally reveal the magnetic phase diagram and theoretically analyze it in terms of spin-flop-like phase transitions. In this case, we observe the dominance of the $\mathrm{Fe}\text{−}\mathrm{Co}$ sublattice, which is a subject of the strong interaction with the $\mathrm{Ta}$ layer. This $\mathrm{Fe}\text{−}\mathrm{Co}$ anisotropy enhancement is expressed in the appearance of abnormal wing-shaped hysteresis loops near the compensation point and, in the unusual phase diagram, where the first-order phase transition line deviates towards low temperatures. This effect can be useful for the design of ultrafast ferrimagnetic devices with desired switching parameters.

A magnetic tunnel junction (MTJ) with orthogonal magnetic anisotropy and consisting of Ta X/Co₄₀Fe₄₀B₂₀ 1.2 (reference)/MgO 2.0/Co₂₀Fe₆₀B₂₀ 2.3 (sensing)/Ta 5/Ru 5 (thickness in nanometers), where X ranges from 15 to 30, is proposed and investigated in response to the demand for out-of-plane field sensors. The reference layer with perpendicular magnetic anisotropy (PMA) demonstrates tuneable coercivity ranging from 72 Oe to 175 Oe. The sensing layer exhibits in-plane anisotropy with the avoidance of exchange coupling from the PMA reference layer because of a thick MgO barrier layer. The magnetization reversal behavior of micron scale devices not only corresponds well to the sheet film, but is also independent in terms of shape and size. The magnetoresistance curve exhibits a ratio of ∼27% in the presence of a perpendicular field and is insensitive to the in-plane field. For perpendicular field sensing, the dynamic range with a sensitivity of ∼0.3%/Oe can achieve ±25 Oe with a coercive field of less than 3 Oe. Additionally, even when bias is applied up to 9.1 mV, magnetic fluctuation still stays below 0.15 mOe.

We report on a theoretical study of thermal magnetization switching induced by nanosecond electric current pulse using Lagrangian formalism based on the Landau–Lifshitz–Gilbert equation. The parameters for modeling are obtained from the measurements of the anomalous Hall resistance at different probe currents. We obtain the switching diagrams, analyze how the switching rate depends on the pulse parameters and the applied magnetic field, and find the optimal set of values such as orientation of the field, electric pulse duration, and energy consumption. We find that the magnetization switching is particularly efficient near the compensation point, where a decrease in the magnetization of the rare-earth sublattices by 10% or less can lead to reversal of net magnetization.

We present a ferromagnetic resonance (FMR) spin pumping experiment at room temperature in periodic arrays of permalloy nanodots of different radii deposited onto a 3D topological insulator Bi₂Se₃ film. We measure the dc voltage signal generated by spin-to-charge conversion of the pumped spin current due to the spin-orbit coupling in the bulk of Bi₂Se₃. In the nanostructured samples, two resonance peaks are observed, associated with Kittel and inhomogeneous edge modes, respectively. This more complex modal composition in comparison to continuous systems may provide additional advantages for development of prospective spintronic devices. We support our experimental results by theoretical calculations, which are based on micromagnetic modeling of the magnetization dynamics under FMR excitation in a nanodot. A numerical approach to the calculation of the spin-pumping voltage is proposed, and the efficiency of spin-to-charge conversion is estimated for two nanostructured samples with different dot sizes.

In this work, we shed light on the mechanism behind the complexity of the anomalous Hall effect (AHE) in the rare earth-transition metal (RE-TM) compound. To achieve a comprehensive picture, we first theoretically investigate the pure elemental metals and observe that the AHE of RE Gd is negative while that of TM Co is positive. We then investigate magnetic properties and AHE behavior for two typical cases of TM-rich and RE-rich compositions that correspond to GdCo5 and GdCo3 alloys, respectively. The observation that net magnetization is not a decisive factor in assessing the AHE value is consistent with recent claims. Besides, our investigations reveal a significant role of the Gd sublattice to the AHE. The reduction AHE signal under a high-applied field is attributed to the counteraction between the positive and negative AHC contributions when the TM and RE sub-moments are aligned parallel. On a bright note, our new findings can be successfully employed to unravel two types of aberrant humps of AHE signals near compensation temperature.