Strong Spin-Orbit Interactions in an InAlAs/InGaAs/InAlAs Two-Dimensional Electron Gas by Weak Antilocalization Analysis

Spin-orbit interactions in a two-dimensional electron gas were studied in an InAlAs/InGaAs/InAlAs quantum well. Since weak anti localization effects take place far beyond the diffusive regime, (i.e., the ratio of the characteristic magnetic field, at which the magnetoresistance correction maximum occurs, to the transport magnetic field is more than ten) the experimental data are examined by the Golub theory, which is applicable to both diffusive regime and ballistic regime. Satisfactory fitting lines to the experimental data have been achieved using the Golub theory. In the strong spin-orbit interaction two-dimensional electron gas system, the large spin splitting energy of 6.08 meV is observed mainly due to the high electron concentration in the quantum well. The temperature dependence of the phase-breaking rate is qualitatively in agreement with the theoretical predictions. (C) 2009 The Japan Society of Applied Physics

Electric-tunable magneto resistance effect in a two-dimensional electron gas modulated by hybrid magnetic-electric barrier nanostructure

The electric-tunable spin-independent magneto resistance effect has been theoretically investigated in ballistic regime within a two-dimensional electron gas modulated by magnetic-electric barrier nanostructure. By including the omitted stray field in previous investigations oil analogous structures, it is demonstrated based on this improved approximation that the magnetoresistance ratio for the considered structure can be efficiently enhanced by a proper electric barrier up to the maximum value depending on the specific magnetic suppression. Besides, it is also shown the introduction of positive electrostatic modulation can effectively overcome the degradation of magnetoresistance ratio for asymmetric configuration and enhance the visibility of periodic pattern induced by the size effect, while for an opposite modulation the system magnetoresistance ratio concerned may change its sign. (C) 2009 Elsevier B.V. All rights reserved.

Magnetointersubband oscillations of the two-dimensional electron gas in AlxGa1-xN/GaN heterostructures

Shubmkov-de Haas (SdH) measurements are performed over a temperature range of 1.5-20K in AL(0.22)Ga(0.78)N/GaN heterostructures with two subbands occupied. In addition to an intermodulation between two sets of SdH oscillations from the first and second subbands, a beating in oscillatory magnetoresistance at 12K is observed, due to the mixing of the first subband SdH oscillations and 'magnetointersubband' (MIS) oscillations. A phase shift of pi between the SdH and MIS oscillations is also clearly identified. Our experimental results, i.e. that the SdH oscillations dominate at low temperature and MIS oscillations dominate at high temperature, fully comply with the expected behaviour of MIS oscillations.

Interplay between s-d exchange interaction and Rashba effect: Spin-polarized transport

The authors investigate the spin-polarized transport properties of a two-dimensional electron gas in a n-type diluted magnetic narrow gap semiconductor quantum well subjected to perpendicular magnetic and electric fields. Interesting beating patterns in the magnetoresistance are found which can be tuned significantly by varying the electric field. A resonant enhancement of spin-polarized current is found which is induced by the competition between the s-d exchange interaction and the Rashba effect [Y. A. Bychkov and E. I. Rashba, J. Phys. C 17, 6039 (1984)]. (c) 2006 American Institute of Physics.

Magnetic properties of silicon doped with gadolinium

The magnetic semiconductor GdxSi1-x was prepared by low-energy dual ion-beam epitaxy. GdxSi1-x shows excellent magnetic properties at room temperature. A high magnetic moment of 10 mu(B) per Gd atom is observed. The high atomic magnetic moment is interpreted as being a result of the RKKY mechanism. The indirect exchange interaction between ions is strong at large distances due to the low state density of the carriers in the magnetic semiconductor.

Magnetic properties and rectifying behaviour of silicon doped with gadolinium

The magnetic/nonmagnetic p-n junction was prepared by implanting gadolinium into the n-type silicon with low-energy dual-ion-beam epitaxy technology. The magnetic layer GdxSi1-x shows excellent magnetic properties at room temperature. High magnetic moment 10mu(B) per Gd atom is observed, which is interpreted by RKKY mechanism. Magnetic/nonmagnetic p-n junctions show rectifying behaviour, but no magnetoresistance is observed.

Interlayer segregation in magnetic multilayers and its influence on exchange coupling

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. X-ray photoelectron spectroscopy shows that Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. While studying Ta/X(X=Bi,Pb,Ag,In)/NiFe/FeMn multilayers, we also find that X atoms segregate to the NiFe/FeMn interface, which results in a decrease of the H-ex. However, a small amount of Bi, Pb, etc. deposited between Cu and pinned NiFe layer for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers can increase H-ex. (C) 2003 American Institute of Physics.

Carrier concentration profiling in magnetic GaMnSb/GaSb investigated by electrochemistry capacitance-voltage profiler

Depth profiles of carrier concentrations in GaMnSb/GaSb are investigated by electrochemistry capacitance-voltage profiler and electrolyte of Tiron. The carrier concentration in GaMnSb/GaSb measured by this method is coincident with the results of Hall and X-ray diffraction measurements. It is indicated that most of the Mn atoms in GaMnSb take the site of Ga, play a role of acceptors, and provide shallow acceptor level(s).

Effects of annealing on properties of spin-valve pinned with FeMn alloy

The magnetic properties of spin-valve pinned by FeMn layer were investigated after it was annealed at different temperatures. Its property was dependent on the vacuum annealing temperature. The pinning field could be increased through annealing at a temporature lower than 200degreesC;the pinning field would reduce and other properties be deteriorated as the annealing temperature was higher than 200degreesC; the pinning effect lost and giantmagnetic resistance disappeared at 300degreesC. Based on the results of AES analysis it was concluded that the diffusion in spin-valve multilayer was along grain boundary.

Longitudinal spin transport in diluted magnetic semiconductor superlattices: The effect of the giant Zeeman splitting

Longitudinal spin transport in diluted magnetic semiconductor superlattices is investigated theoretically. The longitudinal magnetoconductivity (MC) in such systems exhibits an oscillating behavior as function of an external magnetic field. In the weak magnetic-field region the giant Zeeman splitting plays a dominant role that leads to a large negative magnetoconductivity. In the strong magnetic-field region the MC exhibits deep dips with increasing magnetic field. The oscillating behavior is attributed to the interplay between the discrete Landau levels and the Fermi surface. The decrease of the MC at low magnetic field is caused by the s-d exchange interaction between the electron in the conduction band and the magnetic ions. The spin polarization increases rapidly with increasing magnetic field and the longitudinal current becomes spin polarized in strong magnetic field. The effect of spin-disorder scattering on MC is estimated numerically for low magnetic fields and found to be neglectible for our system.

Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (H-ex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta. (C) 2002 American Institute of Physics.

Influence of Fe3+ on perovskite oxides: La2/3Ca1/3Mn1-xFexO3

The structure and magnetoresistance properties in sintered samples of La-2/3 Ca-1/3 Mn1-x FexO3 (0 less than or equal to x less than or equal to 0.84) are studied by using Mossbauer spectroscopy, XRD and magnetic measurement. There are antiferromagnetic interactions between Fe and its nearest neighbors (Fe, Mn) when 0 less than or equal to x less than or equal to 0.67, which are important factors influencing the double-exchange between Mn3+ and Mn4+, Curie temperature, magnetic moment and GMR. It is suggested that the Mn3+(Fe3+)/Mn4+ system also consists of magnetic clusters with different sizes.

Analysis of the interfaces of [NiFe/Mo](30) and [Fe/Mo](30) multilayers

The interface states of [NiFe/Mo](30) and [Fe/Mo](30) multilayers have been investigated by x-ray small angle reflection and diffuse scattering. Significant interface roughness correlation was observed in both ultrathin [NiFe/Mo](30) and [Fe/Mo](30) multilayers. An uncorrelated roughness of about 27-3.1 Angstrom was revealed in the [NiPe/Mo](30) multilayers, which is explained as originating from a transition layer between the NiFe and the Mo layers. By the technique of diffuse scattering, it is clearly indicated that the interfacial roughness of NiFe/Mo is much smaller than that of Fe/Mo although the lattice mismatch is the same in both multilayers.

Electronic states of a two-dimensional electron system in a lateral superlattice and a perpendicular magnetic field

The electronic state of a two-dimensional electron system (2DES) in the presence of a perpendicular uniform magnetic field and a lateral superlattice (LS) is investigated theoretically. A comparative study is made between a LS induced by a spatial electrostatic potential modulation (referred to as a PMLS) and that induced by a spatial magnetic-field modulation (referred ro asa MMLS). By utilizing a finite-temperature self-consistent Hartree-Fock approximation scheme; the dependence of the electronic state on different system parameters (e.g., the modulation period, the modulation strength, the effective electron-electron interaction strength, the averaged electron density, and the system temperature) is studied in detail. The inclusion of exchange effect is found to bring qualitative changes to the electronic state of a PMLS, leading generally to a nonuniform spin splitting, and consequently the behavior of the electronic state becomes similar to that of a MMLS. The Landau-level coupling is taken into account, and is found to introduce some interesting features not observed before. It is also found that, even in the regime of intermediate modulation strength, the density dependence of the spin splitting of energy levels, either for a PMLS or a MMLS, can be qualitatively understood within the picture of a 2DES in a perpendicular magnetic field with the modulation viewed as a perturbation. [S0163-1829(97)02248-0].

Anomalous shift of the beating nodes in illumination-controlled In1-xGaxAs/In1-yAlyAs two-dimensional electron gases with strong spin-orbit interaction

The beating patterns in the Shubnikov-de Haas oscillatory magnetoresistance originating from zero-field spin splitting of two-dimensional electron gases (2DEGs) in In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As quantum wells with silicon delta doped on the upper barrier layer have been investigated by means of magnetotransport measurements before and after illumination. Contrary to the expectation, after each illumination, the beating nodes induced by the zero-field spin-splitting effect shift to lower and lower magnetic field due to the decrease in the zero-field spin-splitting energy of the 2DEGs. The anomalous phenomenon of the shift of the beating nodes and the decrease in spin-orbit coupling constants after illumination cannot be explained by utilizing the previous linear Rashba model. It is suggested that the decrease in the zero-field spin-splitting energy and the spin-orbit coupling constant arise from the nonlinear Rashba spin splitting.