We measure the THz emission of a layered spintronic system based on platinum (Pt) and terbium–iron (Tb x Fe1–x ) alloys for the entire range of Tb content (0 ≤ x ≤ 1) under different external applied magnetic fields. We find that the THz emission amplitude closely follows the in-plane magnetization. Deviations occur when the ferrimagnetic TbFe layer changes from an in-plane to an out-of-plane easy axis at x = 0.2, and in the medium composition range x = 0.45–0.55, where Tb magnetic moments dominate the total magnetic moment. The increasing influence of Tb also leads to an inverted THz amplitude for samples with comparable Fe and Tb contents. The THz emission is highest for Tb x Fe1–x /Pt samples with small amounts of Tb (x = 0.03–0.15) due their reduced electrical conductivity compared to pure Fe/Pt and strongly decreases with increasing Tb content by 2 orders of magnitude. Our systematic study paves the way for designing optimized spintronic THz emitters and demonstrates that transient THz spectroscopy is a powerful tool to gain insight into complex magnetic systems.

We present a spintronic terahertz emitter based on a ferrimagnetic gadolinium-iron alloy (GdxFe1−x) and platinum (Pt). We measure the magnetic-field-dependent terahertz emission of GdxFe1−x/Pt spintronic heterostructures in the entire composition range (0 ≤ x ≤ 1). Excellent agreement is found between the measured data and a theoretical model based on the ratio of in-plane and saturation magnetization, up to a Gd content of x = 0.4 for all applied fields. At a higher Gd content (x ≥ 0.6), the measured terahertz amplitudes and the model deviate, due to the increasing influence of Gd. The GdxFe1−x/Pt emitters share similar properties with TbxFe1−x/Pt emitters, such as a strong increase in terahertz emission for a small rare earth content. However, our systematic study demonstrates that the terahertz emission amplitude of GdxFe1−x/Pt is up to 17 times higher than that of TbxFe1−x/Pt, which is important for the use and further optimization of these spintronic emitters operating at room temperature.

In this Letter, we present a material system with two ferrimagnetic GdxFe100-x layers where the relative orientation of the Fe magnetic moments can be set by temperature in the presence of an external magnetic field. We demonstrate that, depending on the relative alignment of the Fe moments, the spintronic emitter system can be either in a high- or in a low-amplitude terahertz emitting state. Nonmagnetic metal layers with opposite spin Hall angles were utilized for further improvement of the efficiency. This study opens a route for an efficient type of spintronic terahertz emitter system based on the ferrimagnetic properties of rare earth-3d transition metal alloys, which allows switching the emission state from high to low power.

instance spin, orbital, and valley magnetic moments) band structure of a material. [2][3][4][5][6][7] Therefore, FR spectroscopy (FRS) is a powerful method in physics, chemistry, and biology. Some notable examples include the magnetic response and domain structures of solids, [2,8] optically detected nuclear magnetic resonances in fluids, [9,10] sensitive detection of paramagnetic molecules in gas mixtures, [11] biochemical and for biomolecular detection, [12] spin coherence probing in cold atoms, [13,14] investigation of quantum spin fluctuations, [15] and laser-frequency stabilization. [16] It is also used to perform Zeeman spectroscopy of many-body quasiparticles in solids, such as neutral and charged excitons. [2,17] As such, it is of fundamental importance to investigate the magnetic response of materials as a function of the photon energy. [18] It is because their characteristic band structures have energy-dependent spin-polarized density of states and van Hove singularities which possess prominent magnetic responses. [18,19] FRS provides this information with high sensitivity, under magnetic field (B) strengths of the order of 1 T or less, which are also suitable for device applications. [2] With the recent advancements in the area of 2D semiconductors and magnets, [17,[20][21][22][23][24][25][26] FRS naturally emerges as a method for studying their magnetic-field-dependent band structures.A major challenge while performing temperature-dependent (typically liquid He temperature up to room temperature) A Faraday rotation spectroscopy (FRS) technique is presented for measurements on the micrometer scale. Spectral acquisition speeds of about two orders of magnitude faster than state-of-the-art modulation spectroscopy setups are demonstrated. The experimental method is based on charge-coupled-device detection, avoiding speed-limiting components, such as polarization modulators with lock-in amplifiers. At the same time, FRS spectra are obtained with a sensitivity of 20 µrad (0.001°°) over a broad spectral range (525-800 nm), which is on par with state-of-the-art polarization-modulation techniques. The new measurement and analysis technique also automatically cancels unwanted Faraday rotation backgrounds. Using the setup, Faraday rotation spectroscopy of excitons is performed in a hexagonal boron nitride-encapsulated atomically thin semiconductor WS 2 under magnetic fields of up to 1.4 T at room temperature and liquid helium temperature. An exciton g-factor of −4.4 ± 0.3 is determined at room temperature, and −4.2 ± 0.2 at liquid helium temperature. In addition, FRS and hysteresis loop measurements are performed on a 20 nm thick film of an amorphous magnetic Tb 20 Fe 80 alloy.

Magnetic bistability between vortex and single domain states in nanostructures are of great interest from both fundamental and technological perspectives. In soft magnetic nanostructures, the transition from a uniform collinear magnetic state to a vortex state (or vice versa) induced by a magnetic field involves an energy barrier. If the thermal energy is large enough for overcoming this energy barrier, magnetic bistability with a hysteresis-free switching occurs between the two magnetic states. In this work, we tune this energy barrier by tailoring the composition of FePd alloys, which were deposited onto self-assembled particle arrays forming magnetic vortex structures on top of the particles. The bifurcation temperature, where a hysteresis-free transition occurs, was extracted from the temperature dependence of the annihilation and nucleation field which increases almost linearly with Fe content of the magnetic alloy. This study provides insights into the magnetization reversal process associated with magnetic bistability, which allows adjusting the bifurcation temperature range by the material properties of the nanosystem.