We utilized microwave spectroscopy to study the magnetization oscillations locally induced in a Permalloy film by a pure spin current, which is generated due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency is lower than the ferromagnetic resonance of Permalloy, indicating that the oscillation forms a self-localized nonpropagating spin-wave soliton. At cryogenic temperatures, the spectral characteristics are remarkably similar to the traditional spin-torque nano-oscillators driven by spin-polarized currents. However, the linewidth of the oscillation increases exponentially with temperature and an additional peak appears in the spectrum below the ferromagnetic resonance, suggesting that the spectral characteristics are determined by interplay between two localized dynamical states.

We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films. The possibility to induce dynamical states of nanomagnets or change their static configuration by the currentinduced spin torque (ST) [1, 2] has stimulated intense research into current-induced phenomena in magnetic systems. While the early experiments utilized spin-polarized electric currents in magnetic multilayers [3,4], recent studies focused on the effects of spin current produced due to the spin-orbit interaction (SOI) in bilayers of ferromagnets (F) with heavy nonmagnetic metals (N) [5][6][7][8]. The spin-orbit effects that contribute to the currentinduced phenomena include the spin Hall effect (SHE) originating from SOI in N, the Rashba effect [9] and the Dzyaloshinskii-Moriya interaction (DMI) [10], both originating from the broken inversion symmetry at the F/N interface. The DMI produces chiral effective fields that can result in nontrivial topological magnetic structures such as spirals, skyrmions and chiral domain walls [11].

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We present a comprehensive study of the reversal process of perpendicular magnetization in thin layers of the ferromagnetic semiconductor Ga 1-x Mn x As. For this investigation we have purposely chosen Ga 1-x Mn x As with a low Mn concentration (x ≈ 0.02), since in such specimens contributions of cubic and uniaxial anisotropy parameters are comparable, allowing us to identify the role of both types of anisotropy in the magnetic reversal process. As a first step we have systematically mapped out the angular dependence of ferromagnetic resonance in thin Ga 1-x Mn x As layers, which is a highly

A narrow-gap ferromagnetic In 1Ϫx Mn x Sb semiconductor alloy was grown by low-temperature molecular-beam epitaxy on CdTe/GaAs hybrid substrates. Ferromagnetic order in In 1Ϫx Mn x Sb was unambiguously established by the observation of clear hysteresis loops both in direct magnetization measurements and in the anomalous Hall effect, with Curie temperatures T C ranging up to 8.5 K.The observed values of T C agree well with the existing models of carrier-induced ferromagnetism.

We study the effects of electrostatic gating on the current-induced phenomena in ultrathin ferromagnet/heavy metal heterostructures. We utilize heterodyne detection and analysis of symmetry with respect to the direction of the magnetic field to separate electric field contributions to the magnetic anisotropy, current-induced field-like torque, and damping torque. Analysis of the electric field effects allows us to estimate the Rashba and the spin Hall contributions to the current-induced phenomena. Electrostatic gating can provide insight into the spin-orbit phenomena, and enable new functionalities in spintronic devices.

The effect of modulation doping by Be on the ferromagnetic properties of Ga 1-x Mn x As is investigated in Ga 1-x Mn x As/Ga 1-y Al y As heterojunctions and quantum wells. Introducing Be acceptors into the Ga 1-y Al y As barriers leads to an increase of the Curie temperature T C of Ga 1-x Mn x As, from 70 K in undoped structures to over 100 K with the modulation doping. This increase is qualitatively consistent with a multi-band mean field theory simulation of carriermediated ferromagnetism. An important feature is that the increase of T C occurs only in those structures where the modulation doping is introduced after the deposition of the magnetic layer, but not when the Be-doped layer is grown first. This behavior is expected from the strong sensitivity of Mn interstitial formation to the value of the Fermi energy during growth.

We demonstrate that electrochemical capacitance voltage profiling can be used to determine the free hole concentration in heavily p-type doped low-temperature-grown GaAs films. This provides a simple and reliable method for measuring the hole concentration in ferromagnetic Ga 1-x Mn x As semiconductor alloys. The method overcomes the complications that arise from the anomalous Hall effect term which affects standard transport studies of carrier concentration in conducting ferromagnetic materials.Specifically, we find that the maximum Curie temperature of about 111 K found for our where N Mn is the concentration of uncompensated magnetic (Mn) spins that are coupled by indirect ferromagnetic interaction, p is the hole concentration, and C is a constant specific to the host material. It is seen from Eq.(1) that in order to increase T C one has to increase the concentration of uncompensated Mn ++ ions, N Mn , and/or the hole concentration, p. Alternatively, it has also been proposed that the ferromagnetic coupling between Mn ++ ions is mediated by holes localized on adjacent ions [6].Two key parameters common to most proposed models explaining the indirect fe rromagnetic coupling and predicting the Curie temperature in Ga 1-x Mn x As are the free hole concentration and the concentration of uncompensated Mn ++ ions [5,6]. One of the long standing problems impeding the analysis of these hole-mediated magnetic interactions that underlie the ferromagnetism in III-Mn-V semiconductor alloys has been the difficulty to reliably determine the hole concentration. The Hall effect which is commonly used to measure the concentration of charge carriers in semiconductors cannot be applied at normally available magnetic fields to materials like Ga 1- In this paper we show that the free hole concentration in ferromagnetic Ga 1-x Mn x As thin films can be reliably measured using the electrochemical capacitancevoltage (ECV) method. To demonstrate this, we first use ECV profiling to measure the hole concentration in a series of nonmagnetic p-type Ga 1-y Be y As layers grown by LT-MBE, and compare these results with Hall effect data obtained on the same samples. Additionally, valuable information has also been obtained from comparison of ECV andHall data observed on non-ferromagnetic Ga 1-x-y Mn x Be y As layers that were grown in conditions very similar to those used for the growth of ferromagnetic Ga 1-x Mn x As layers.The Ga 1-x Mn x As, Ga 1-y Be y As and Ga 1-x-y Mn x Be y As films were grown on semiinsulating (001) GaAs substrates in a Riber 32 R&D MBE system. Fluxes of Ga, Be and Mn were supplied from standard effusion cells, and As 2 flux was produced by a cracker cell. Prior to film deposition we grew a 450 nm GaAs buffer layer at 590ºC (i.e., under normal GaAs growth conditions). The substrate was then cooled down for the growth of a 3 nm thick low-temperature (LT) GaAs, followed by either a 110 nm Ga 1-x Mn x As layer, 4 or 230 nm thick layer of either Ga 1-y Be y As or Ga 1-x-y Mn x Be y As. The As 2 :Ga beam equival...