Dependence Of Spin Polarization Research Articles

All-optical spin-dependent polarization switching in Bragg-spaced quantum well structures

All-optical polarization switching is demonstrated in a resonant photonic band-gap structure consisting of Bragg-spaced quantum wells (BSQWs). The switch takes advantage of the large spin-dependent optical nonlinearities and the ultrafast recovery present in BSQWs to produce large throughputs (greater than 40%), high contrast ratios (greater than 40 dB), and large optical bandwidths (∼0.6THz), where both switching time and sample recovery time are control-pulse-width limited.

Magnetic Field Dependence of Electron Spin Polarization Generated through Radical−Triplet Interactions

The magnetic field dependence of electron spin polarization (ESP), generated in free radicals when they encounter photoexcited triplets, was measured experimentally and analyzed theoretically. The time-resolved electron paramagnetic resonance measurements were performed with a microwave setup consisting of low-loss dielectric ring resonators with tunable microwave frequencies and the corresponding magnetic fields. The ESP of the radical was found in the magnetic field range of 170-370 mT, and the results of the calculation based on the numerical solution of the stochastic Liouville equation were found to be in line with the experimental data showing that ESP decreases when the magnetic field increases.

Spin Polarization Dependence of the Coulomb Drag at Largers

We find that the temperature dependence of the drag resistivity between two dilute two-dimensional hole systems exhibits an unusual dependence upon spin polarization. Our main observation is that near the apparent metal-insulator transition, the temperature dependence of the drag, given by Talpha, weakens significantly with the application of a parallel magnetic field (B(||)), with alpha saturating at half its zero field value for B(||)>B(*), where B(*) is the polarization field.

Rydberg atoms in a magnetic quadrupole field

We study electronically excited atoms exposed to a magnetic quadrupole field. In order to describe the electron dynamics, a one-body approach is employed. Due to the inhomogeneity of the field, the spatial and spin degrees of freedom become coupled in a unique way. The underlying unitary and anti-unitary symmetries are discussed in detail leading to remarkable features such as a two-fold degeneracy of any energy level. We analyse the energy level structure throughout a wide range of field gradients. An investigation of the electronic spin properties is performed by studying the spatially dependent spin-polarization which exhibits a rich nodal structure. We compute wavelengths and strengths for electromagnetic transitions and provide the selection rules. A discussion of the so-called ellipsoidal states which exhibit unique properties such as large mean orbital angular momenta and spatial compactness is provided. The property of magnetic field-induced permanent electric dipole moments is analysed in detail. Wherever reasonable, the results obtained for the quadrupole field are compared to the homogeneous field case.

Spin-orbit splitting of the Shockley state in theAg∕Au(111)interface

We have studied the modification of Au(111) surface state parameters with Ag deposition. We unambiguously evidence a continuous decrease in the spin-orbit splitting of the two surface state subbands upon increasing Ag coverage. An annealing leads to the formation of a chemically disordered Ag-Au alloy. This alloy formation is accompanied by an increase in the spin-orbit splitting. We established a quantitative correlation between the amplitude of this splitting and the relative amount of Au and Ag atoms probed by the surface state wave function proving the atomic character of the spin-orbit splitting. Control of the Ag-Au interface allows a continuous fine tuning of surface state properties; in particular, the $k$-dependent spin polarization.

플라즈마 산화시간과 열처리 조건에 따른 터널링 자기저항비의 온도의존특성에 관한 연구

We have studied to understand the barrier and interface qualities and structural changes through measuring temperature dependent spin-polarization as functions of plasma oxidation time and annealing time. Magnetic tunnel junctions consisting of SiO2/Ta 5/CoFe 17/IrMn 7.5/CoFe 5/Al 1.6-Ox/CoFe 5/Ta 5 (numbers in nm) were deposited and annealed when necessary. A 30 s,40 s oxidized sample showed the lowest spin-polarization values. It is presumed that tunneling electrons were depolarized and scattered by residual paramagnetic Al due to under-oxidation. On the contrary, a 60s, 70 s oxidized sample might have experienced over-oxidation, where partially oxidized magnetic dead layer was formed on top of the bottom CoFe electrode. The magnetic dead layer is known to increase the probability of spin-flip scattering. Therefore it showed a higher temperature dependence than that of the optimum sample (50 s oxidation). temperature dependence of 450 K annealed samples was improved when the as-deposited one compared. But the sample underwent 475 K and 500 K annealing exhibits inferior temperature dependence of spin-polarization, indicating that the over-annealed sample became microstucturally degraded.

Anomalous magnetization of nanoscale ferromagnet/normal-metal systems: Possible evidence of the electronic spin polarization

The magnetization of two nanoscale ferromagnet/normal-metal systems, random mixtures of Ni-Ag and arrays of Co clusters embedded in a Pt matrix, have been studied down to 0.3 K by means of conventional magnetometry and by the extraordinary Hall effect measurements in fields up to 17 T. Unusually high values and an anomalous temperature dependence of the saturated magnetization in the low temperature limit have been found in both systems. We suggest that the phenomenon is evidence of the temperature dependent spin polarization of the conducting electrons in the normal-metal matrix.

Interplay between shape and magnetocrystalline anisotropies in patterned bcc Fe/Co(001) multilayers

In this work the interplay between magnetocrystalline and shape anisotropies was studied in submicron size particles made of bcc Fe/Co(001) multilayers of thickness 20 nm and Co content in the range 27--75 at. %. Arrays of circular and elliptical particles with well-defined geometry and lateral sizes in the range 150--550 nm were prepared by electron-beam lithography and ion milling and investigated by magnetization measurements and magnetic force microscopy (MFM). The angular dependence of the magnetization of the initial films demonstrates the change of the easy direction of magnetization (in plane) from [100] to [110] as one goes from pure Fe to Fe/Co multilayers with increasing Co content. The first-order anisotropy constant ${K}_{1}$ is negative for the investigated Fe/Co films and depends linearly on the Co concentration. By extrapolation, the change of sign is obtained at about 23 at. % of Co. The high effective magnetic moment of the multilayers, up to $(2.8\ifmmode\pm\else\textpm\fi{}0.3){\ensuremath{\mu}}_{B}$ per atom for the Fe2/Co6 multilayer film, may be explained by an enhancement of the local moments both on Fe and Co and a spin dependent polarization of the electron gas, due to confinement in the individual (0.3--1.2 nm thick) Fe and Co layers. The domain structure and magnetization reversal processes of circular particles (diameter 550 nm) are governed by the shape anisotropy for the nearly isotropic Fe8/Co3 multilayers and by the high magnetocrystalline anisotropy in Fe2/Co6 multilayers. The MFM investigation of elliptical particles with aspect ratio 1:3 reveals that only in the case with cooperating shape and strong magnetocrystalline anisotropies a stable single domain state is formed in the majority (78%) of the elements. From magnetization measurements we deduce that the elliptical particles are in quasisingle domain states (so called C and S states) during magnetization reversal.

Spin dependent transitions of charged excitons in type-II quantum wells

We present results of the reflection, the absorption, and the photoluminescence measurements performed on ZnMgBeSe/ZnSe/BeTe quantum wells. In n-doped samples the reflection and the absorption spectra have shown a typical negatively charged exciton feature in spin-dependent polarization under magnetic field. The pronounced linear polarization of the photoluminescence indicates that photoluminescence transitions of an indirect type take place at respective interfaces of ZnSe/BeTe/ZnSe. A new type of charged excitons peculiar to the type-II quantum structures has been proposed.

Spin polarization of phase delay time in a magnetic–electric barrier structure

AbstractThe spin‐dependent phase delay time of two‐dimensional electrons through a magnetic–electric barrier structure with/without an external electric field has been systematically investigated. The dependence of electron spin polarization on the applied bias, the incident wave vector, the incident electron energy and the height of the electric barrier has been addressed. It is found that the magnetic–electric barrier structure exhibits significant spin polarization under an external electric field, especially for electrons with small energies, where the spin polarization also displays a considerable wave vector‐dependent feature. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Bias and temperature dependence of hot electron transport in a spin-valve structure

We have explored spin-dependent hot electron transport in a magnetic tunneling junction at finite temperatures. The inelastic mean-free path has been extracted from either theoretical calulations or experimental measurements. The temperature dependence of hot electron spin polarization has been modeled according to P0[1−(T/Tc)3/2]. The bias dependence of magnetocurrent agrees in trend with experiments, which indicates that the model adopted here indeed displays the key factors in these phenomena.

Spin-density inversion symmetry driven first-order magnetic phase transition inGaCMn3

The first-order magnetic phase transtion of the metallic perovskite ${\mathrm{GaCMn}}_{3}$ has been investigated in terms of density-functional theory using the all-electron total-energy full-potential linearized augmented plane-wave method. We found that the antiferromagnetic (AFM) state is more stable energetically than the ferromagnetic (FM) state at the low-temperature lattice constant. Total-energy calculations yield a critical lattice constant of $7.3411\mathrm{a}.\mathrm{u}.,$ which is remarkably close to the experimental one $(7.34\mathrm{a}.\mathrm{u}.)$ The calculated magnetic moments of Mn in each magnetic state are almost constant with lattice-constant variation, $\ensuremath{\sim}1.58{\ensuremath{\mu}}_{\mathrm{B}}$ for the FM and $\ensuremath{\sim}1.80{\ensuremath{\mu}}_{\mathrm{B}}$ for the AFM states, which are very close to experiment. The FM spin density is found to have even inversion symmetry, while the AFM one has odd, which restricts the direction of the AFM ordering vector along the [111] direction via tilting of the orbital orientation axis. Hence, the spin-density parity about the spin-inversion symmetry may be a key for understanding the first-order phase transition in ${\mathrm{GaCMn}}_{3}.$ We also found that the oddness of the spin-density-inversion symmetry in the AFM state brings about the wave-function sign dependent spin polarization and changes the bonding character. From the calculated density of states, the hybridization between the $\mathrm{Ga}\ensuremath{-}4p$ and $\mathrm{Mn}\ensuremath{-}3d$ states is important for determining the magnetism of ${\mathrm{GaCMn}}_{3}.$

Temperature dependent induced spin polarization in Cr 2O 3 overlayers on epitaxial CrO 2 films

Spin-resolved inverse photoemission investigations show that the native Cr 2O 3 surface is antiferromagnetically coupled to the CrO 2 thin film substrate, with a temperature dependent induced polarization. The Cr 2O 3 exhibits the characteristic behavior of a rigid band/spin mixing behavior (non-Stoner) of a local moment paramagnet. The strong shifts of the conduction band edge from room temperature to low temperature suggests that the extent of the induced polarization of the Cr 2O 3 oxide surface, by the CrO 2 substrate, may be partly related to Coulomb blockade effects identified in CrO 2/Cr 2O 3/CrO 2 junctions.

The magnetic field dependence of the electron spin polarization in consecutive spin correlated radical pairs in type I photosynthetic reaction centres

The magnetic field/microwave frequency dependence of the spin polarized EPR spectra of the sequential spin correlated radical pairs P+A− 1 and P+F− x in type I photosynthetic reaction centres is investigated. Experimental data are presented for photosystem (PS) I and reaction centres of heliobacteria at × band (9.7 GHz) and K band (24 GHz). In photosystem I at ambient temperatures the lifetime of A − 1 is ~290 ns and both states are observable by transient EPR. In heliobacteria, electron transfer to Fx occurs within ~600 ps and only the state P+F− x is observed. The experimental data show a net polarization of P+ in the state P+F− x, which displays a clear dependence on the strength of the external field. The net polarization generated in sequential radical pairs is expected to pass through a maximum as a function of the Zeeman energy when the characteristic time of singlet-triplet mixing is comparable with the lifetime of the precursor. In PS I, the precursor lifetime (290ns) is much longer than the characteristic time of singlet-triplet mixing at × band (9 GHz, 3 kG) and K band (24 GHz, 8 kG). As a result, the observable net polarization decreases with the field strength in this region. In contrast, in heliobacteria, the precursor lifetime (600 ps) is much shorter than the characteristic time of singlet-triplet mixing, and the net polarization increases in the same range of Zeeman energies. The polarization patterns in these two systems can be described using the specific limiting cases of a short lived and long lived precursor radical pair and written as a sum of several contributions. The spectra are simulated on this basis using parameters derived entirely from independent experimental data, and good agreement between the experimental polarization patterns is obtained. The calculated polarization patterns are sensitive to spin dynamics on a timescale much shorter than the spectrometer response time, and the expected influence of a 10 ns component in the electron transfer, as observed optically in some PS I, preparations is discussed. No significant influence from such a component is found in the spin polarization patterns of PS I from the cyanobacterium Synechocystis 6803.

Spin polarization spectra of strained superlattices

Optical spin orientation in the strained short-period semiconductor superlattices is investigated theoretically. Strong features in the spin polarization dependence on the electron energy are identified with the Van-Hove singularities in absorption spectra. The maximum polarization values found to be in the range of 70–94% are more sensitive to the absorption edge smearing than in the case of strained layer structures. Calculated polarization spectra are close to the experimental spectra of polarized electron emission.

Field-domain spintronics in magnetic semiconductor multiple quantum wells

We develop a theory of nonlinear growth direction transport in magnetically doped II-VI compound semiconductor multiple-quantum-well systems. We find that the formation of electric field domains can be controlled by manipulating the space dependence of the band electron spin polarization, using its exchange coupling to local moments. We emphasize the importance of band electron spin relaxation in limiting the strength of these effects.

Temperature dependence of magnetocurrent in spin-valve transistor: a phenomenological study

The temperature dependence of magnetocurrent in the spin-valve transistor has been theoretically explored based on phenomenological model. We find that temperature dependence of the collector current strongly depends on the relative orientation of magnetic moment of ferromagnetic metals due to spin mixing effect. For example, the parallel collector current is decreasing with increasing temperatures, while the anti-parallel collector current is increasing. We then obtain decreasing magnetocurrent with increasing temperatures. The result accords with the experimental data in qualitative manner. Along with this, we find that temperature dependence of hot electron spin polarization can also contribute to the magnetocurrent at finite temperatures. This phenomenological model calculations suggest that it is essential to understand the relative importance of spin mixing effect and hot electron spin polarization in the spin-valve transistor at finite temperatures.

Spin effects in the 2D electron gas

Spin affects the properties of the electron gas in a subtle way. The quantitative and, in fact, even the qualitative determination of spin dependent properties in this system requires calculations of extreme accuracy. Here, we review predictions of fixed-node diffusion Monte Carlo simulations with Slater–Jastrow as well as backflow nodes for the 2D electron gas at zero temperature, focusing on the spin-polarization dependence of the ground state energy and on the occurrence of spontaneous spin-polarization. We also analyze the enhancement of the spin susceptibility (with respect to the Pauli value), over a wide range of densities. Finally we discuss the form of effective electron–electron interactions that may be used to estimate the possibility of spontaneous superconductivity in the 2D electron gas.

Imaging Self-Organized Domains at the Micron Scale in Antiferromagnetic Elemental Cr Using Magnetic X-ray Microscopy

ABSTRACTThe 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.

Recent progress in high-resolution magnetic imaging using scanning probe techniques

We have applied magnetic force microscopy (MFM) and spin-polarized scanning tunnelling spectroscopy (SP-STS) in ultrahigh vacuum (UHV) to study the magnetic domain structure of Co/Au(111) and Gd/W(110), respectively. A new measurement mode will be presented which minimizes possible accidental interactions between the probe tip and the sample in UHV-MFM. This allows the investigation of the well known spin reorientation transition of Co films grown on Au(111) at nanometre-scale spatial resolution. Details of domain walls and the domain structure as a function of CO coverage are studied. Spin-polarized tunnelling is realized by using an Fe-coated W tip and a sample which exhibits an exchange-split surface state. Magnetic domain imaging with a spatial resolution below 20 nm is demonstrated for Gd/W(110). The observed bias dependent spin polarization of Gd(0001) is in good agreement with spin-resolved inverse photoemission spectroscopy results.