Quantitative determination of spin-orbit-induced magnetic field in GaMnAs by field-scan planar Hall measurements.

Spin-orbit-induced (SOI) effective magnetic field in GaMnAs film with in-plane magnetic anisotropy has been investigated by planar Hall effect measurements. The presence of SOI field was identified by a shift between planar Hall resistance (PHR) hystereses observed with positive and negative currents. The difference of switching fields occurring between the two current polarities, which is determined by the strength of the SOI field, is shown to depend on the external field direction.

Exchange bias in ferromagnetic bilayers with orthogonal anisotropies: the case of GaMnAsP/GaMnAs combination.

We report the observation of exchange bias in a ferromagnetic GaMnAsP/ GaMnAs bilayer, in which the easy axis in one layer is oriented out-of-plane, and in the other in-plane. Magnetization reversal in this system is explored using planar Hall effect (PHE) measurements under various initial conditions and with various field-cooling orientations. Our results show that the two magnetic layers are ferromagnetically exchange-coupled, and that such coupling results in pronounced exchange-bias-like shifts of magnetic hysteresis loops during reversal of in-plane magnetization.

Nanoscale Metastable ε-FeN Ferromagnetic Materials by Self-Sustained Reactions.

A single-step method for the preparation of metastable ε-FeN nanoparticles by combustion of reactive gels containing iron nitrate (Fe(NO)) and hexamethylenetetramine (CHN) in an inert atmosphere is reported. The results of Fourier transform infrared spectroscopy (FTIR) and thermal analysis coupled with dynamic mass spectrometry revealed that the exothermic decomposition of a coordination complex formed between Fe(NO) and HMTA is responsible for the formation of ε-FeN nanoscale particles with sizes of 5-15 nm. The magnetic properties between 5 and 350 K are characterized using a superconducting quantum interference device (SQUID) magnetometer, revealing a ferromagnetic behavior with a low-temperature magnetic moment of 1.

Interlayer exchange coupling in ferromagnetic semiconductor trilayers with out-of-plane magnetic anisotropy.

We report the observation of ferromagnetic (FM) and antiferromagnetic (AFM) interlayer exchange coupling (IEC) in GaMnAsP-based trilayer structures with out-of-plane magnetic anisotropy. Magnetization and anomalous Hall effect (AHE) measurements show well-resolved magnetization transitions corresponding to the two GaMnAsP layers. Minor loop measurements reveal a characteristic shift caused by IEC in all trilayer samples investigated.

Ultrafast manipulation of topologically enhanced surface transport driven by mid-infrared and terahertz pulses in BiSe.

Topology-protected surface transport of ultimate thinness in three-dimensional topological insulators (TIs) is breaking new ground in quantum science and technology. Yet a challenge remains on how to disentangle and selectively control surface helical spin transport from the bulk contribution. Here we use the mid-infrared and terahertz (THz) photoexcitation of exclusive intraband transitions to enable ultrafast manipulation of surface THz conductivity in BiSe.

Magnetization reversal and interlayer exchange coupling in ferromagnetic metal/semiconductor Fe/GaMnAs hybrid bilayers.

We report a detailed study of magnetization reversal in Fe/GaMnAs bilayers carried out by magnetotransport measurements. Specifically, we have used planar Hall resistance (PHR), which is highly sensitive to the direction of magnetization, and is therefore ideally suited for tracking magnetization as it reorients between successive easy axes in the two magnetic layers during reversal. These reorientations take place separately in the two magnetic layers, resulting in a series of different magnetization alignments (parallel or orthogonal) during reversal, providing a series of stable PHR states.

Magnetization reversal in trilayer structures consisting of GaMnAs layers with opposite signs of anisotropic magnetoresistance.

Magnetization reversal in a GaMnAs trilayer system consisting of two GaMnAs layers separated by a Be-doped GaAs spacer was investigated by magnetotransport measurements. The rotation of magnetization in the two GaMnAs layers is observed as two abrupt independent transitions in planar Hall resistance (PHR). Interestingly, one GaMnAs layer manifests a positive change in PHR, while the other layer shows a negative change for the same rotation of magnetization.

Field-free manipulation of magnetization alignments in a Fe/GaAs/GaMnAs multilayer by spin-orbit-induced magnetic fields.

We investigate the process of selectively manipulating the magnetization alignment in magnetic layers in the Fe/GaAs/GaMnAs structure by current-induced spin-orbit (SO) magnetic field. The presence of such fields manifests itself through the hysteretic behavior of planar Hall resistance observed for two opposite currents as the magnetization in the structure switches directions. In the case of the Fe/GaAs/GaMnAs multilayer, hystereses are clearly observed when the magnetization switches direction in the GaMnAs layer, but are negligible when magnetization transitions occur in Fe.

Non-volatile logic gates based on planar Hall effect in magnetic films with two in-plane easy axes.

We discuss the use of planar Hall effect (PHE) in a ferromagnetic GaMnAs film with two in-plane easy axes as a means for achieving novel logic functionalities. We show that the switching of magnetization between the easy axes in a GaMnAs film depends strongly on the magnitude of the current flowing through the film due to thermal effects that modify its magnetic anisotropy. Planar Hall resistance in a GaMnAs film with two in-plane easy axes shows well-defined maxima and minima that can serve as two binary logic states.

Observation of uniaxial anisotropy along the [100] direction in crystalline Fe film.

We report an observation of uniaxial magnetic anisotropy along the [100] crystallographic direction in crystalline Fe film grown on Ge buffers deposited on a (001) GaAs substrate. As expected, planar Hall resistance (PHR) measurements reveal the presence of four in-plane magnetic easy axes, indicating the dominance of the cubic anisotropy in the film. However, systematic mapping of the PHR hysteresis loops observed during magnetization reversal at different field orientations shows that the easy axes along the and are not equivalent.

Simultaneous Enhancement of Electrical Conductivity and Thermopower of Bi₂Te₃ by Multifunctionality of Native Defects.

Simultaneous increases in electrical conductivity (up to 200%) and thermopower (up to 70%) are demonstrated by introducing native defects in Bi2 Te3 films, leading to a high power factor of 3.4 × 10(-3) W m(-1) K(-2). The maximum enhancement of the power factor occurs when the native defects act beneficially both as electron donors and energy filters to mobile electrons.

Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band.

The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied material for prototype applications in semiconductor spintronics. Because ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has direct and crucial bearing on its Curie temperature T(C). It is vigorously debated, however, whether holes in (Ga,Mn)As reside in the valence band or in an impurity band.

Use of the asymmetric planar hall resistance of an Fe film for possible multi-value memory device applications.

Systematic planar Hall measurements have been performed on a ferromagnetic Fe film grown on a standard (001) GaAs substrate at room temperature. The angular dependence of the planar Hall effect revealed the presence of both four-fold (cubic) and two-fold (uniaxial) anisotropies in the 7 nm thick Fe film. The dominance of the four-fold symmetric anisotropy, however, provided four magnetic easy axes near the (100) direction, which results in a two step switching phenomenon in the magnetization reversal process.

Coherent magnetization precession in ferromagnetic (Ga,Mn)As induced by picosecond acoustic pulses.

We show that the magnetization of a thin ferromagnetic (Ga,Mn)As layer can be modulated by picosecond acoustic pulses. In this approach a picosecond strain pulse injected into the structure induces a tilt of the magnetization vector M, followed by the precession of M around its equilibrium orientation. This effect can be understood in terms of changes in magnetocrystalline anisotropy induced by the pulse.

Giant Zeeman splitting in nucleation-controlled doped CdSe:Mn2+ quantum nanoribbons.

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.

Observation of insulating nanoislands in ferromagnetic GaMnAs.

Resonant Raman data on ferromagnetic GaMnAs reveal the existence of a new kind of defect: insulating nanoislands consisting of substitutional MnGa acceptors surrounded by interstitial MnI donors. As indicated by the observation of a sharp 1S3/2-->2S3/2 Raman transition at approximately 703 cm(-1), the acceptor-bound holes inside the islands are isolated from the metallic surroundings. Instead, Mn-bound excitons do couple to the ferromagnetic environment, as shown by the presence of associated Raman magnon side bands.

Origin of magnetic circular dichroism in GaMnAs: giant zeeman splitting versus spin dependent density of states.

We present a unified interpretation of experimentally observed magnetic circular dichroism (MCD) in the ferromagnetic semiconductor (Ga,Mn)As, based on theoretical arguments, which demonstrates that MCD in this material arises primarily from a difference in the density of spin-up and spin-down states in the valence band brought about by the presence of the Mn impurity band, rather than being primarily due to the Zeeman splitting of electronic states.

Carrier-mediated antiferromagnetic interlayer exchange coupling in diluted magnetic semiconductor multilayers Ga1-xMnxAs/GaAs:Be.

We report the antiferromagnetic (AFM) interlayer exchange coupling between Ga0.97Mn0.03As ferromagnetic semiconductor layers separated by Be-doped GaAs spacers.

Spatially resolved inhomogeneous ferromagnetism in (Ga,Mn)as diluted magnetic semiconductors: a microscopic study by muon spin relaxation.

Thin epitaxial films of the diluted magnetic semiconductor (DMS) GaMnAs have been studied by low energy muon spin rotation and relaxation (LE-microSR) as well as by transport and magnetization measurement techniques. LE-microSR allows measurements of the distribution of magnetic field on the nanometer scale inaccessible to traditional macroscopic techniques. The spatial inhomogeneity of the magnetic field is resolved: although homogeneous above Tc, below Tc the DMS consists of ferromagnetic and paramagnetic regions of comparable volumes.

Anomalous hall effect in the (in,mn)sb dilute magnetic semiconductor.

High magnetic field study of Hall resistivity in the ferromagnetic phase of (In,Mn)Sb allows one to separate its normal and anomalous components. We show that the anomalous Hall term is not proportional to the magnetization, and that it even changes sign as a function of magnetic field. We also show that the application of pressure modifies the scattering process, but does not influence the Hall effect.

Spin-polarizable excitonic luminescence in colloidal Mn2+-doped CdSe quantum dots.

The photoluminescence of colloidal Mn2+-doped CdSe nanocrystals has been studied as a function of nanocrystal diameter. These nanocrystals are shown to be unique among colloidal doped semiconductor nanocrystals reported to date in that quantum confinement allows tuning of the CdSe bandgap energy across the Mn2+ excited-state energies. At small diameters, the nanocrystal photoluminescence is dominated by Mn 2+ emission.

Ultrafast enhancement of ferromagnetism via photoexcited holes in GaMnAs.

We report on the observation of ultrafast photoenhanced ferromagnetism in GaMnAs. It is manifested as a transient magnetization increase on a 100 ps time scale, after an initial subpicosecond demagnetization. The dynamic magnetization enhancement exhibits a maximum below the Curie temperature T(c) and dominates the demagnetization component when approaching T(c).

Stable multidomain structures formed in the process of magnetization reversal in GaMnAs ferromagnetic semiconductor thin films.

The process of magnetization reversal in ferromagnetic Ga(1-x)Mn(x)As epilayers has been systematically investigated using the planar Hall effect (PHE). Interestingly, we have observed a pronounced asymmetry in the PHE hysteresis when the range of the field scan is restricted to fields below the final magnetization transition. The observed behavior indicates that (a) multidomain structures are formed as M undergoes a reorientation, (b) the domain landscape formed in this way remains stable even after the magnetic field is switched off, and (c) the reorientation of magnetization directions corresponding to the transition points in PHE takes place separately within each domain.

Magnetic scattering of spin polarized carriers in (In, Mn)Sb dilute magnetic semiconductor.

Magnetoresistance measurements on the magnetic semiconductor (In, Mn)Sb suggest that magnetic scattering in this material is dominated by isolated Mn2+ ions located outside the ferromagnetically ordered regions when the system is below T(c). A model is proposed, based on the p-d exchange between spin-polarized charge carriers and localized Mn2+ ions, which accounts for the observed behavior both below and above the ferromagnetic phase transition. The suggested picture is further verified by high-pressure experiments, in which the degree of magnetic interaction can be varied in a controlled way.