We have investigated the values of the Rashba spin-orbit coupling constant α in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells using an anti-weak-localization (AWL) analysis as a function of quantum well asymmetry. We have found that the deduced α values have strong correlations with the structural inversion asymmetry of the pertinent quantum wells as predicted theoretically. This fact suggests that the AWL analysis provides a reliable way to deduce α values experimentally for designing future spintronics devices.

We analyzed the spin-dependent conductivity in the system of paramagnetic quantum dots embedded in semi-insulating matrix, which is due to bound magnetic polaron (BMP) inter-dot hopping. If such a system is characterized by wide distributions of the “bare” electron energies and BMP shifts, variable-range and variable-polaron-barrier hopping can be observed at low temperaturesT. It results in the giant magnetoresistance,ρ(H, T ) governed by a non-activation law, lnρ /α [T0(H)/T ]p, whereT0(H) drops with magnetic field,H. Depending on the conditions, parameters of the material, and the dimensionality of the system, the exponent 0.25 < p < 0.75. This type ofT -dependence has been observed in GaMnAs and MnGe magnetic semiconductors.

Magneto-optical spectroscopy in combination with tunable laser excitation spectroscopy is employed to carry out a detailed study of spin alignment and spin injection in II-VI wide-bandgap semiconductor heterostructures, aiming at optimization of structural design for nano-scale spintronic applications. The use of tunable excitation is shown to provide a valuable opportunity to monitor separately spin relaxation and spin injection processes in the structures. Efficient spin alignment is achieved by using a diluted magnetic semiconductor (DMS) (a layer of ZnMnSe or a ZnMnSe/CdSe superlattice) as thin as 10 nm. The spin alignment efficiency is shown to depend critically on the ratio between the rates of spin relaxation and spin transport within the DMS layer. This allows the realization of spin alignment and spin switching functions by varying the structural design.

Fe films on GaAs substrates have evolved as a model system for the integration of magnetic materials with semiconductors. We report on in situ stress measurements of Fe/GaAs(001), which enlighten the dynamics of the interface formation of this important magnetic metal/semiconductor system. At deposition temperatures of 300 K and 450 K, the stress evolution during growth is very similar. In Fe films thicker than 6–7 nm, the stress is compressive owing to the misfit between the lattices of Fe and GaAs. Thinner films surprisingly are dominated by a tensile stress contribution due to considerable As (and Ga) interdiffusion even at 300 K. Magnetization and in-plane anisotropy of both films are bulk-like.

Fast switching from conductor to insulator induced by laser light illumination has been studied in single crystals and thin films of La1−xSrxMnO3 in the range of the ferromagnetic phase transition. Based on our experimental data on the photoresponse as a function of temperature, electric current, and intensity, we have demonstrated that the switching and relaxation processes are determined by heating and heat conduction processes. The relaxation time, specific heat and the latent heat constants have been estimated.

A spin rectifying diode, which utilizes Rashba spin-orbit coupling, is proposed using semiconducting triple barrier structures. This spin diode makes use of spin-dependent resonant tunneling levels that are formed in the triple barrier structures. We found that, for a certain emitter-collector bias voltage, it is possible to engineer the structure in such a way that a resonant l evel formed within the first quantum well matches that of the second quantum well only for a selected spin state, thus realizing an electronic spin rectifier. The calculated spin polarization of the transmitted current through the device, which is defined as I↑–I↓/(I↑+I↓), is found to be higher than 99.9%.

The domains of antiferromagnetic order in elemental chromium can be observed with spatial resolution that is improved by orders of magnitude in comparison with previous techniques using magnetic x-ray scattering with an incident x-ray beam focused to a submicron spot. This use of magnetic x-ray microscopy takes advantage of the incommensurate spin density wave order in Cr to isolate magnetic scattering. The spin polarization dependence of the magnetic x-ray scattering cross section allows the first order spin-flip transition near 120 K to be imaged directly.

We present a thermodynamic study of the critical magnetic properties of La1.2Sr1.8Mn2O7, including the determination of the fundamental characteristics of a magnetic system: anisotropy, critical exponents and crossovers in the vicinity of the Curie temperature, TC∼108K. It appears that two-dimensional correlations above TC do not spread very fast, and that thus the critical fluctuations regime occurs in a moderately narrow temperature range, assessing the three- dimensional nature of the ferromagnetic ordering.

Epitaxial growth of the ferromagnetic semiconductors GaMnP:C and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP:C films grown with 9.4% Mn are found to be p-type with hysteretic behavior to room temperature. GaMnN films grown at 700 °C with 2.8% Mn show hysteresis at 300 K, while temperature-dependent magnetization measurements indicate that the magnetism may persist to much higher temperatures (> 325 K). Samples of AlGaMnN have also been prepared for the first time that show improved surface morphology compared to GaMnN but which show only paramagnetic behavior.

The effects of the growth conditions and the lattice strains of pulsed laser deposited (PLD) La0.7Sr0.3MnO3 (LSMO) thin films upon the magnetic behavior have been studied using magneto-optical Kerr effect (MOKE) at room temperature. First, the structural quality of the films was investigated by XRD and the surface morphology was studied using AFM. It is shown that both surface morphology and crystallinity are optimized when the target-to-substrate distance and the oxygen pressure are chosen in agreement with a PD3 scaling law. Secondly, hysteresis loops have been recorded along the [100], [110] and [001] directions and the easy directions of magnetization have been determined for both stress states, i.e. tension on SrTiO3 and compression on LaAlO3. In tensile films, the whole plane is found to be easy, whereas, in compressive films, the easy axis should be an intermediate direction between the film's plane and its normal. Moreover, tensile films deposited under optimized growth conditions exhibit the largest anisotropy coefficient (K1eff = -6.9×105 erg/cm3).

Extent of Mn diffusion to the plasma-oxidized AlOx tunnel barrier of magnetic tunnel junction was examined using Auger Electron Spectroscopy (AES) and X-Ray Photoelectron Spectroscopy (XPS). A magnetic film stack consisting of Ta/AlOx/CoFe/IrMn/NiFe/Ta was deposited with the AlOx layer treated under different plasma oxidation durations. AES depth profiles showed that Mn diffusion to the AlOx/CoFe interface increased with increasing oxidation after annealing at 300°C. XPS analysis indicated that Mn found at the CoFe/AlOx interface in the over-oxidized electrode was in the form of MnO2. Our research suggests that Mn diffusion was accelerated by preferential oxidation of Mn at the CoFe/AlOx interface.

Ion beam sputter deposition (IBSD) techniques for deposition of giant magnetoresistance (GMR) films have been studied using an automated IBSD system designed and built in-house. We have studied the properties of Fe/Cr multilayers deposited using either Ar or Xe ions with the primary ion beam energy varying from 500 eV to 1100 eV. The films were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), magnetization measurements, and magnetoresistance measurements. The maximum value of GMR obtained was 49% (measured at 10K). For the Cr spacer thickness layer chosen, this GMR ratio is larger than the values reported for polycrystalline Fe/Cr multilayers deposited by magnetron sputtering. In general, we have found that GMR ratios for the Fe/Cr multilayers increase with decreasing primary ion beam energy, and are greater for films deposited using Xe ions than for films deposited using Ar ions. We explain the observed effects on the basis of energy distributions of sputtered atoms and backscattered working gas atoms (neutrals). The energy distributions were calculated using TRIM (Transport of Ions in Matter) software based on the Monte Carlo method.

The magnetic properties of cubic (3C) silicon carbide (SiC) doped by first row transition metals (TM) are studied within the local spin density functional approach using the linearized muffin-tin orbital (LMTO) method in the atomic sphere approximation (ASA). The magnetic properties are found to depend strongly on the doping site. For the preferred doping site (Si), Cr and Mn exhibit the most pronounced magnetic behavior with Cr favoring ferromagnetic coupling and Mn antiferromagnetic coupling.

By using a rather simple model potential we calculate the influence of specular and diffuse scattering at interfaces on the resistance for currents perpendicular to the plane of the layers (CPP) in multilayered metallic structures. We find that if one maintains the same interfaces between layers, their contribution to the total resistance of the system depends on the thickness of the intervening layers. Their contribution is constant only if the distance between interface is larger than the electron mean free path in the bulk of the layers. The error incurred by neglecting the dependence of the interface resistance on layer thickness depends on the amount of diffuse scattering at interfaces and the height of the potential step at the interface. For a Fe-Cr or Co-Cu multilayer consisting of three or five layers with realistic interfaces where both specular and diffuse scattering may occur, the error reaches 15-20%; this exceeds the experimental error. We suggest systems where this effect may be observed.

The atomic and electronic structure of Co/SrTiO3/Co (001) magnetic tunnel junctions (MTJs) was investigated by first-principles density-functional theory. We considered different interface terminations and the most stable structure with the TiO2 termination has been identified based on energetics of adhesion. The electronic structure of the TiO2-erminated MTJ shows an exchange coupling between the interface Co and Ti atoms mediated by oxygen. This coupling induces the magnetic moment of 0.25 μB on the interface Ti atom, which is aligned antiparallel to the magnetic moment of the Co layer. We argue that this might cause the inversion of the spin polarization of tunneling across the SrTiO3 barrier that was found in recent experiments.

We present an extensive physical characterization of La2/3Ca1/3MnO3 (LCMO) epitaxial films grown on SrTiO3 (STO), LaAlO3 (LAO) and NdGaO3 (NGO) substrates. The main difference among these substrates is that they have a different mismatch (∼ 1.2%, -1.8% and - 0.1%, respectively) with the manganite. The films can be coherently grown up to 180 nm for STO and NGO but partial relaxation is observed for LAO. The magnetotransport data indicate that very thin films (<27nm) display non-conventional magnetoresistive properties: a substantial magnetoresistance develops which can be progressively appreciated for STO and LAO films. 55Mn-Nuclear Magnetic Resonance experiments on all these films reveal the presence of non-homogeneous electronic states. These experiments in fact provide clear evidence of the presence of two distinguishable ferromagnetic Mn states and a non-ferromagnetic phase. The possible role of strain-induced charge localization is discussed. It turns out that electronic phase separation occurs in all films irrespectively of the particular substrate used; thus we conclude that strain is not the unique driving force for charge localization.

To study the effect of the film/substrate interface in thin films we have analyzed the thickness dependence of the transport properties of SrRuO3 films grown on SrTiO3 substrates. Our data makes evident the failure of the so-called deadlayer model to describe the observed thickness dependence of the conductivity. This is interpreted as due to a non-monotonous change of microstructure as thickness increases. Indeed, Atomic Force Microscopy studies indicate substantial modifications of the growth mechanism with thickness.

Magnetic tunnel junctions of Co0.9Fe0.1/SrTiO3 (STO)/ La0.7Sr0.3MnO3 (LSMO) with a spin-valve structure having an antiferromagnetic MnIr layer have been fabricated by sputtering. Junction magnetoresistance (MR) behavior and its dependence on the bias voltage are examined for junctions with epitaxial STO barrier formed under different sputtering conditions. Spin dependent transport measurements show that these junctions exhibit spin-valve type MR loops with an inverse (positive) MR of the ratio of 14-22 % at 4.2 K. The inverse MR observed is asymmetric with respect to the bias voltage direction. Stoichiometric STO barrier, as characterized by Rutherford backscattering (RBS) analysis, is found to result in very large asymmetric bias dependence, while the junctions with nonstoichiometric STO barrier exhibit the symmetric bias dependence. Our results suggest that the nonstoichiometry of STO barrier modifies the electronic structures of electrode/barrier interfaces, and thereby reducing the asymmetry of bias voltage dependence of junction MR.

It is shown that monopolar optical spin orientation of free carriers in zinc-blende structure based quantum wells (QWs) causes an electric current which reverses its direction upon changing the helicity of the radiation from left to right circular polarization resulting in a circular photogalvanic effect. The monopolar non-equilibrium population of spin-up and spin-down states has been achieved by far-infrared optical excitation ofp- andn-type GaAs/AlGaAs QWs structures. Two methods are introduced allowing to determine spin relaxation times. One is based on the Hanle effect in magnetic field induced circular photogalvanic effect, the other is spin sensitive bleaching of absorption. In contrast to usually applied methods of optical spin orientation, in the present case of terahertz excitation only one kind of charge carriers is involved in spin orientation and relaxation processes.

The electronic band-edge spectrum of magnetic semiconductor quantumwells containing a diluted magnetic semiconductor as one of the constituents is studied within the envelope-function formalism. Quantum wells with normal and mutually inverted band arrangements are considered. The sp – d hydribization between the bare sp-electron states and the d-states of the Mn atoms is shown to lead to a spin-splitting effect. The spin-splitting effect is studied as a function of external magnetic field, well width, valence band offset and fraction of magnetic atoms. The results have bearing on the perspective for using the magnetic semicondutor structures in spin electronics.