Bulk—like contribution of tunnel magnetoresistance in magnetic tunnel junctions

We have demonstrated that the bulk-like contribution to tunnelling magnetoresistance (TMR) exists in the magnetic tunnel junctions, and is determined by the tunnelling characteristic length of the ferromagnetic electrodes. In the experiment, a wedge-shaped CoFe layer is inserted at the interface between the insulating barrier and the reference electrode. It is found that TMR ratio increases from 18% without CoFe layer to a saturation value of 26.5% when the CoFe thickness is about 2.3 nm. The tunnelling characteristic length, l_{tc}, can be obtained to be about 0.8 nm for CoFe materials.     

Barrier height and negative tunnel magnetoresistance

Based on the free-electron approximation method proposed by Slonczewski, we substitute the finite magnetic zone by a semi-infinite magnet. On this basis, the relationship between the tunnel magnetoresistance (TMR) and the barrier height of magnetic tunnel junction (MTJ) is studied. We find the TMR at small bias is always positive for various barrier heights when the MTJ has a symmetric configuration and the negative TMR can be observed when MTJ is with lower barrier height in the asymmetric condition.     

Low-field magnetoresistance of strongly modulated two-dimensional electron gas

The typical form of the low-field magnetoresistance anomaly induced by a strong one-dimensional periodic modulation of the background potential is described. It is shown that the magnetoresistance peak due to the magnetic breakdown is always followed by a resistance increase at higher magnetic fields, for which οcτ > 1.     

Large oscillating tunnel magnetoresistance in ferromagnetic graphene single tunnel junction

Spin-polarized transports of relativistic electrons through graphene-based ferromagnet/insulator/ferromagnet (FG/IG/FG) single junctions have been investigated theoretically. Large oscillating tunnel magnetoresistance (TMR) has been found in monolayer and bilayer FG/IG/FG junctions. The oscillating amplitudes of TMR do not decrease with the increase of the thickness and the height of barrier, in contrast to the exponential decay in conventional ferromagnet/insulator/ferromagnet single junction. The physical origin for such a phenomenon has also been analyzed. It is anticipated to apply such a phenomenon to design the spin-polarized electron device based on the graphene materials.     

磁性隧道结的隧穿磁电阻效应及其研究进展

文章概括地介绍了磁性隧道结(MTJs)的隧穿磁电阻(TMR)效应的产生机理和特点,主要用途和研究背景以及最近几年的研究进展和现状.对用Al2O3和MgO做绝缘势垒层的MTJs进行了对比,指出用MgO做绝缘势垒层的MTJs的优点.文章还阐明了交换偏置自旋阀(EB-SV)型MTJs的问题和不足,以及新兴的赝自旋阀(PSV)型MTJs的优势.文章最后总结了用于MTJs的各种铁磁层和绝缘势垒层材料,并对TMR材料今后的研究和开发作了展望.     

Oscillations of tunnel magnetoresistance in ferromagnet-insulator-ferromagnet structures

A model of spin-dependent electron transport in ferromagnet-insulator-ferromagnet structures that takes into account the potential relief, applied voltage, image forces, and scattering by the potential relief is developed. It is shown that tunnel magnetoresistance oscillations are caused by the nonmonotonic energy dependence of transmission coefficients and their split in the molecular field of the ferromagnet. Conditions are found under which the tunnel magnetoresistance is virtually independent of scattering by the interfaces.     

磁性隧道结的隧穿磁电阻效应及其研究进展

文章概括地介绍了磁性隧道结（MTJs）的隧穿磁电阻（TMR）效应的产生机理和特点,主要用途和研究背景以及最近几年的研究进展和现状.对用Al2O3和MgO做绝缘势垒层的MTJs进行了对比,指出用MgO做绝缘势垒层的MTJs的优点.文章还阐明了交换偏置自旋阀（EB-SV）型MTJs的问题和不足,以及新兴的赝自旋阀（PSV）型MTJs的优势.文章最后总结了用于MTJs的各种铁磁层和绝缘势垒层材料,并对TMR材料今后的研究和开发作了展望.     

Spatially modulated antiferromagnetic structures in an easy-plane multiferroic

Possible types of spatially modulated periodic antiferromagnetic structures in a uniaxial rhombohedral multiferroic with BiFeO₃ crystal symmetry have been studied depending on the ratio of the uniaxial anisotropy and magnetoelectric interaction parameters. It has been shown that, along with symmetric cycloid antiferromagnetic structures with zero transverse component of the antiferromagnetism vector, there are changes in the antiferromagnetism vector direction with both right and left nonzero components of the antiferromagnetic moment, which are branched from the high-symmetry spatially modulated distribution. These solutions degenerate into a homogeneous state at a critical value of the normalized easy-plane anisotropy parameter. The existence of the found spatially inhomogeneous antiferromagnetic states with an incommensurate period can lead to additional features in magnetoelectric properties in multiferroics of the type under consideration near magnetic phase transitions in electric and magnetic fields.     

Temperature dependence of the tunneling magnetoresistance for tunnel junctions

The temperature dependence of the tunneling magnetoresistance (TMR) for magnetic tunneling junctions is investigated experimentally before and after the sample is annealed. As grown, the TMR is observed to increase with temperature from 80 to 160 K. A modified Julliere model in conjunction with a spin-dependent two-step tunneling is suggested to describe this temperature dependence.     

Spin-polarized current and tunnel magnetoresistance in heterogeneous single-barrier magnetic tunnel junctions

Current in heterogeneous tunnel junctions is studied in the framework of the parabolic conduction-band model. The developed model of the electron tunneling takes explicitly into account the difference of effective masses between ferromagnetic and insulating layers and between conduction subbands. Calculations for Fe/MgO/Fe-like structures have shown the essential impact of effective mass differences in regions (constituents) of the structure on the tunnel magnetoresistance of the junction.     

Interpretation of the magnetoresistance in doped magnetic tunnel junctions

We present a quantum mechanical model of the magnetoresistance in ferromagnetic tunnel junctions artificially doped by the introduction of layers of impurities in the middle of the barrier. The electron transport across the barrier is described by a combination of direct tunneling, tunneling assisted by spin-conserving scattering and tunneling assisted by spin-flip scattering. With this model, we interpret recent experimental results concerning the dependence of the TMR amplitude on the amount of impurities in the barrier and on temperature. Received 1st February 2001 and Received in final form 14 June 2001     

Spatially modulated phase in the holographic description of quark-gluon plasma

We present a string theory construction of a gravity dual of a spatially modulated phase. Our earlier work shows that the Chern-Simons term in the five-dimensional Maxwell theory destabilizes the Reissner-Nordstr?m black holes in anti-de Sitter space if the Chern-Simons coupling is sufficiently high. In this Letter, we show that a similar instability is realized on the world volume of 8-branes in the Sakai-Sugimoto model in the quark-gluon plasma phase. Our result suggests a new spatially modulated phase in quark-gluon plasma when the baryon density is above 0.8Nf fm(-3) at temperature 150 MeV.     

Tunneling anisotropic magnetoresistance: a spin-valve-like tunnel magnetoresistance using a single magnetic layer

We introduce a new class of spintronic devices in which a spin-valve-like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets. The effect is observed in a normal-metal-insulator-ferromagnetic-semiconductor tunneling device. This behavior is caused by the interplay of the anisotropic density of states in (Ga,Mn)As with respect to the magnetization direction and the two-step magnetization reversal process in this material.     

Spatially modulated polarimetry based on a vortex retarder and Fourier analysis

We report a spatially modulated polarimetry scheme by using a zero-order vortex half-wave retarder(ZVHR)and a spatial Fourier analysis method.A ZVHR is employed to analyze the input polarized light and convert it into a vectorial optical field,and an analyzer is set after the ZVHR to form an hourglass intensity pattern due to the spatial polarization modulation.Then,the input light’s Stokes parameters can be calculated by spatial Fourier analysis of the hourglass pattern with a single shot.The working principle of the polarimeter has been analyzed by the Stokes-Mueller formalism,and some quantitative measuring experiments of different polarization states have been demonstrated.The experimental results indicate that the proposed polarimeter is accurate,robust,and simple to use.     

Flux-dependent tunnel magnetoresistance in parallel-coupled double quantum dots

The tunnel magnetoresistance (TMR) in an Aharonov–Bohm interferometer with two quantum dots inserted in its arms, which is attached to ferromagnetic leads with parallel and antiparallel magnetic configurations, is theoretically studied by means of the nonequilibrium Green’s function technique. We pay particular attention to the influence of an applied magnetic flux on the characteristics of the TMR. In the linear response regime (the external bias voltage V→0) and when the electrons are free from intradot Coulomb interaction, the magnetic flux only changes the peak or dip positions of the TMR. But in the presence of intradot Coulomb repulsion, its peak or dip positions, signs and magnitude are tuned by the magnetic flux. For the nonlinear response regime (V≠0), the TMR is symmetric with respect to zero bias voltage and the magnetic flux can influence its magnitude, signs and the peak positions regardless of the existence of intradot Coulomb interaction. The behavior of the TMR is interpreted in terms of the quantum interference (Fano) effect.     

Spatially modulated vacua in a Lorentz-invariant scalar field theory

The European Physical Journal C - The cosmological principle assumes that the universe is homogeneous and isotropic on cosmic scales. There exist many works testing the cosmic homogeneity and/or...