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Magnetization switching at the interface between ferromagnetic and paramagnetic metals, controlled by current-induced torques, could be exploited in magnetic memory technologies. Compelling questions arise regarding the role played in the switching by the spin Hall effect in the paramagnet and by the spin-orbit torque originating from the broken inversion symmetry at the interface. Of particular importance are the antidamping components of these current-induced torques acting against the equilibrium-restoring Gilbert damping of the magnetization dynamics. Here, we report the observation of an antidamping spin-orbit torque that stems from the Berry curvature, in analogy to the origin of the intrinsic spin Hall effect. We chose the ferromagnetic semiconductor (Ga,Mn)As as a material system because its crystal inversion asymmetry allows us to measure bare ferromagnetic films, rather than ferromagnetic-paramagnetic heterostructures, eliminating by design any spin Hall effect contribution. We provide an intuitive picture of the Berry curvature origin of this antidamping spin-orbit torque as well as its microscopic modelling. We expect the Berry curvature spin-orbit torque to be of comparable strength to the spin-Hall-effect-driven antidamping torque in ferromagnets interfaced with paramagnets with strong intrinsic spin Hall effect. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance is the most widely used technique for characterizing ferromagnetic materials. However, its use is generally restricted to wafer-scale samples or specific micro-magnetic devices, such as spin valves, which have a spatially varying magnetization profile and where ferromagnetic resonance can be induced by an alternating current owing to angular momentum transfer. Here we introduce a form of ferromagnetic resonance in which an electric current oscillating at microwave frequencies is used to create an effective magnetic field in the magnetic material being probed, which makes it possible to characterize individual nanoscale samples with uniform magnetization profiles. The technique takes advantage of the microscopic non-collinearity of individual electron spins arising from spin-orbit coupling and bulk or structural inversion asymmetry in the band structure of the sample. We characterize lithographically patterned (Ga,Mn)As and (Ga,Mn)(As,P) nanoscale bars, including broadband measurements of resonant damping as a function of frequency, and measurements of anisotropy as a function of bar width and strain. In addition, vector magnetometry on the driving fields reveals contributions with the symmetry of both the Dresselhaus and Rashba spin-orbit interactions. [ABSTRACT FROM AUTHOR]

Controlling the magnetization by low-voltage charge depletion in field-effect transistors has been a formidable challenge due to the typically large carrier concentrations in ferromagnets compared to semiconductors. Here we demonstrate that this concept is viable in an all-semiconductor, p-n junction transistor utilizing a thin-film ferromagnetic (Ga,Mn)As channel. We report gate-dependent Curie temperature and magnetoresistance, and persistent magnetization switchings induced by short electrical pulses of a few volts. [ABSTRACT FROM AUTHOR]

Magnetotransport constitutes a useful probe to understand the interplay between electronic band topology and magnetism in spintronic devices. A recent theory of Lu and Shen [Phys. Rev. Lett. 112, 146601 (2014)] on magnetically doped topological insulators predicts that quantum corrections Δκ to the temperature dependence of conductivity can change sign across the Curie transition. This phenomenon has been attributed to a suppression of the Berry phase of the topological surface states at the Fermi level, caused by a magnetic energy gap. Here, we demonstrate experimentally that Δκ can reverse its sign even when the Berry phase at the Fermi level remains unchanged. The contradictory behavior to theory predictions is resolved by extending the model by Lu and Shen to a nonmonotonic temperature scaling of the inelastic scattering length showing a turning point at the Curie transition. [ABSTRACT FROM AUTHOR]

We observe a magnetic-field-induced enhancement of the nonlocal spin signal in Ni80Fe20/Ag lateral spin valves. The enhancement depends on the bias current polarity but not on the field direction. We present a theoretical model that explains our experimental results, taking into account the electron-spin relaxation of magnetic impurities. We find that the relaxation is about an order of magnitude weaker than Elliott-Yafet relaxation. [ABSTRACT FROM AUTHOR]

Intraband and interband contributions to the current-driven spin-orbit torque in magnetic materials lacking inversion symmetry are theoretically studied using the Kuboformula. In addition to the current-driven fieldlike torque TFL=τFLm×uso (uso being a unit vector determined by the symmetry of the spin-orbit coupling), we explore the intrinsic contribution arising from impurity-independent interband transitions and producing an anti-damping-like torque of the form TDL=τDLm×(uso×m). Analytical expressions are obtained in the model case of a magnetic Rashba two-dimensional electron gas, while numerical calculations have been performed on a dilute magnetic semiconductor (Ga,Mn)As modeled by the Kohn-Luttinger Hamiltonian exchange coupled to the Mn moments. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described. [ABSTRACT FROM AUTHOR]

Magnetic linear dichroism and birefringence in (Ga,Mn)As epitaxial layers is investigated by measuring the polarization plane rotation of reflected linearly polarized light when magnetization lies in the plane of the sample. We report on the spectral dependence of the rotation and ellipticity angles in a broad energy range of 0.12-2.7 eV for a series of optimized samples covering a wide range on Mn dopings and Curie temperatures and find a clear blueshift of the dominant peak at energy exceeding the host material band gap. These results are discussed within the framework of the k·p and mean-field kinetic-exchange model of the (Ga,Mn)As band structure. We infer that disorder-induced nondirect transitions significantly influence magneto-optical properties of (Ga,Mn)As. [ABSTRACT FROM AUTHOR]

We investigate the spin polarization of the ferromagnetic semiconductor (Ga,Mn)As by point-contact Andreev reflection spectroscopy. The conductance spectra are analyzed using a recent theoretical model that accounts for momentum- and spin-dependent scattering at the interface. This allows us to fit the data without resorting, as in the case of the standard spin-dependent Blonder-Tinkham-Klapwijk (BTK) model, to an effective temperature or a statistical distribution of superconducting gaps. We find a transport polarization PC≈57%, in considerably better agreement with the k→ · p→ kinetic-exchange model of (Ga,Mn)As, than the significantly larger estimates inferred from the BTK model. The temperature dependence of the conductance spectra is fully analyzed. [ABSTRACT FROM AUTHOR]

Antiferromagnetic hexagonal MnTe is a promising material for spintronic devices relying on the control of antiferromagnetic domain orientations. Here we report on neutron diffraction, magnetotransport, and magnetometry experiments on semiconducting epitaxial MnTe thin films together with density functional theory (DFT) calculations of the magnetic anisotropies. The easy axes of the magnetic moments within the hexagonal basal plane are determined to be along ⟨1100⟩ directions. The spin-flop transition and concomitant repopulation of domains in strong magnetic fields is observed. Using epitaxially induced strain the onset of the spin-flop transition changes from ∼2 to ∼0.5 T for films grown on InP and SrF2 substrates, respectively. [ABSTRACT FROM AUTHOR]