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Our study of magnetization switching in crystalline (Ga,Mn)(As,P) ferromagnetic semiconductor (FMS) film by spin-orbit torque (SOT) has revealed an unexpected increase in critical switching current as the in-plane magnetic bias field is increased beyond a certain point. This intriguing behavior is ascribed to depolarization of spin-polarized current induced by the application of bias field perpendicular to the direction of current carrier spins. This is particularly interesting, because the bias field is itself a necessary requirement for achieving the deterministic SOT magnetization switching. To gain understanding of this unexpected behavior, we incorporated the process of spin depolarization into micromagnetic simulation study of SOT magnetization switching in the (Ga,Mn)(As,P) system. Through simulations that include effects of spin depolarization, we were able to replicate the observed increase in the required critical switching current as the in-plane bias field is increased. Furthermore, our study demonstrates that the dependence of critical switching current on bias field can be quantitatively described by adjusting magnetic anisotropy parameters of the film. This study not only enhances our understanding of SOT phenomena but also offers valuable insights for tailoring and optimizing FMS materials for spintronic applications. [ABSTRACT FROM AUTHOR]

Topologically protected surface current is highly promising for next-generation low-dissipation and disorder-tolerant quantum electronics and computing. Yet, electric transport from the co-existing bulk state dominates the responses of the Dirac surface state, especially at elevated temperatures relevant to technological applications. Here, we present an approach that convincingly showcases the generation, disentanglement, and precise control of enduring surface charge carriers on a topological insulator, Bi2Se3, with high bulk conductivity, all achieved at room temperature. By using pump–probe modulation spectroscopy under ultrabroadband driving tunable from 4 meV to 1.55 eV, we show the terahertz (THz) field-induced surface carriers by discovering their initial temporal responses dominant over high density trivial bulk carriers. Strikingly, the response of the induced surface carrier responses persists for more than ∼5 ps and is enhanced by reducing pump photon energy. The dynamics and lifetime of the distinct surface response manifest themselves as the enhanced THz pump-induced THz transmission, which directly correlates with the transient negative THz conductivity. Increasing the THz driving field reduces the induced surface carrier lifetime and identifies, particularly, an optimal pump field of Es ∼ 224 kV cm−1 for generating the dominant surface response relative to the bulk. This surface carrier dominant regime is suppressed by a joint effect of enhanced surface-bulk scattering and a more rapid saturation of surface excitation compared to the bulk that sets in above Es. The controllability of room temperature topologically surface carriers through pump photon energy offer compelling possibilities for extending this approach to other topological complex materials. [ABSTRACT FROM AUTHOR]

We describe the structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy on GaAs (111) substrates, as revealed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. When the Mn concentration is increased, the lattice of the ternary (Sn,Mn)Se films evolves quasi-coherently from a SnSe2 two-dimensional (2D) crystal structure into a more complex quasi-2D lattice rearrangement, ultimately transforming into the magnetically concentrated antiferromagnetic MnSe 3D rock-salt structure as Mn approaches 50 at. % of this material. These structural transformations are expected to underlie the evolution of magnetic properties of this ternary system reported earlier in the literature. [ABSTRACT FROM AUTHOR]

Using spectroscopic ellipsometry, the dielectric functions of a series of topological insulators, including Bi2Te3, Bi2Se3, and their ternary alloys, were determined. The ellipsometry measurements were obtained using an IR-spectroscopic ellipsometer, spanning a spectral range between 2000 and 35 000 nm. A standard inversion technique was used to model the ellipsometry spectra, which produced the dielectric functions of each of the topological insulator films. These dielectric functions were analyzed further to obtain characteristics such as their bandgap, carrier concentration, and effective mass. Specifically, Kramers–Kronig consistent oscillators were used to represent the Drude contribution as well as the energy gap. The authors found that the bandgap of Bi2(Te1−xSex)3 ternary alloys are larger than their binary constituents (i.e., Bi2Te3 and Bi2Se3). By exploring the temperature dependence of the bandgap, the authors deduced the electron–phonon coupling parameters for the Bi2(Te1−xSex)3 system, using the Bose–Einstein occupation distributions. Compared with Bi2Te3, the authors found that the electron–phonon coupling parameters of the ternary alloys of Bi2(Te1−xSex)3 are smaller. [ABSTRACT FROM AUTHOR]

We studied the thermal conductivity of Bi2Se3, Bi2Te3, and their alloy Bi2(sexTe1-x)3 at room temperature using time-domain thermoreflectance measurements. The Bi2(sexTe1-x)3 films with various concentrations of Se and Te prepared by molecular beam epitaxy on GaAs substrates were investigated to study the dependence of thermal conductivity on film composition. We observed that the Bi2(sexTe1-x)3 ternary alloys can have much lower thermal conductivity values compared to those of Bi2Se3 and Bi2Te3. These results may provide useful information for developing and engineering low thermal conductivity materials for thermoelectric applications. [ABSTRACT FROM AUTHOR]

We discuss magnetic properties of lithographically patterned nanoscale stripes of dilute ferromagnetic semiconductor (Ga,Mn)As aligned with [110] crystallographic direction, i.e., perpendicular to the easy axis of uniaxial magnetocrystalline anisotropy of this material. We find that at temperatures where uniaxial anisotropy becomes dominant, shape-induced effects strongly compete with this intrinsic property, tending to align the total magnetization along the stripe direction. The present study revealed, however, that low-temperature annealing of the stripes markedly reduces such shape-induced effects. This effect of annealing is not presently understood, and will require further detailed study. [ABSTRACT FROM AUTHOR]

We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn1-xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications. [ABSTRACT FROM AUTHOR]

Doping of semiconductor nanocrystals by transition-metal ions has attracted tremendous attention owing to their nanoscale spintronic applications. Such doping is, however, difficult to achieve in low-dimensional strongly quantum confined nanostructures by conventional growth procedures. Here we demonstrate that the incorporation of manganese ions up to 10% into CdSe quantum nanoribbons can be readily achieved by a nucleation-controlled doping process. The cation-exchange reaction of (CdSe)13 clusters with Mn2+ ions governs the Mn2+ incorporation during the nucleation stage. This highly efficient Mn2+ doping of the CdSe quantum nanoribbons results in giant exciton Zeeman splitting with an effective g-factor of ∼600, the largest value seen so far in diluted magnetic semiconductor nanocrystals. Furthermore, the sign of the s–d exchange is inverted to negative owing to the exceptionally strong quantum confinement in our nanoribbons. The nucleation-controlled doping strategy demonstrated here thus opens the possibility of doping various strongly quantum confined nanocrystals for diverse applications. [ABSTRACT FROM AUTHOR]

A series of Ga1-xMnxAs1-yPy thin films grown on GaAs (100) substrates by molecular beam epitaxy were systematically investigated to establish the effect of phosphorous on structural and magnetic properties of the alloy. Detailed characterization of both as-grown and annealed samples by x-ray diffraction and magnetometry were carried out. Reciprocal space map scans confirmed that the quaternary alloy is fully strained by the substrate throughout its thickness. Magnetization measurements revealed a clear trend of decreasing Curie temperature with increasing P concentration, and revealed that the magnetic easy axis gradually turns from in-plane to out-to-plane orientation as P concentration increases. [ABSTRACT FROM AUTHOR]

A systematic study of low temperature (LT) annealing III1-xMnxV of (Ga1-xMnxAs and Ga1-xMnxAs1-yPy) thin films in situ with different capping layers (Se, Te, or As) was carried out without exposure to the atmosphere. Experimental results show that a correct in situ annealing approach can lead to significant increases of the Curie temperature, carrier concentration, and magnetic moment, similar to the ex situ LT-annealing experiments achieved in earlier studies. Moreover, this approach allowed us to successfully deposit high-quality semiconductor layers on top of such in situ annealed films, demonstrating great potential for designing high quality III1-xMnxV-based multilayers for spintronic applications optimized by the benefits of the LT-annealing. [ABSTRACT FROM AUTHOR]