Spin flip conductance of quantum nanocontacts

The theory of nanosize point contacts made of ferromagnetic metals is developed. A general quantum scattering theory is applied to calculate conductance of the nanocontact with domain wall located in the constriction. Exact solution of the electron motion in the potential of the linear domain wall is used as a zero-order approximation. Spin-conserving and spin-flip conductivities are calculated by perturbation theory up to the second order in difference between the model and actual potentials of the domain wall. The spin-flip conductivity imposes natural limitation on magnetoresistance of a point contact, which otherwise diverges in the regime of quantized conductance through the contact

Tunneling magnetoresistance in ferromagnetic planar hetero-nanojunctions

We present a theoretical study of the tunneling magnetoresistance (TMR) in nanojunctions between non-identical ferromagnetic metals in the framework of the quasiclassical approach. The lateral size of a dielectric oxide layer, which is considered as a tunneling barrier between the metallic electrodes, is comparable with the mean-free path of electrons. The dependence of the TMR on the bias voltage, physical parameters of the dielectric barrier, and spin polarization of the electrodes is studied. It is demonstrated that a simple enough theory can give high TMR magnitudes of several hundred percent at bias voltages below 0.5 V. A qualitative comparison with the available experimental data is given. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Resonant tunnel magnetoresistance in a double magnetic tunnel junction

We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FML/I/FMW/I/FMR, where the magnetization of the middle ferromagnetic metal layer FMW can be aligned parallel or antiparallel with respect to the fixed magnetizations of the left FML and right FMR ferromagnetic electrodes. The transmission coefficients for components of the spin-dependent current, and TMR are calculated as a function of the applied voltage. As a result, we found a high resonant TMR. Thus, DMTJ can serve as highly effective magnetic nanosensor for biological applications, or as magnetic memory cells by switching the magnetization of the inner ferromagnetic layer FMW.© Springer Science+Business Media, LLC 2011

Impact of lattice strain on the tunnel magnetoresistance in Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 magnetic tunnel junctions

The objective of this work is to describe the tunnel electron current in single-barrier magnetic tunnel junctions within an approach that goes beyond the single-band transport model. We propose a ballistic multichannel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single-crystal magnetic Fe(110) electrodes for Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO 3 tunnel junctions, where the electronic band structures of Fe and La0.67Sr0.33MnO3 are derived by ab initio calculations. © 2013 American Physical Society

Anomalous Tunnel Magnetoresistance and Spin Transfer Torque in Magnetic Tunnel Junctions with Embedded Nanoparticles

The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature

Tunnel magnetoresistance in magnetic tunnel junctions with embedded nanoparticles

© 2015 IEEE. We present a theoretical simulation to calculate the tunnel magnetoresistance (TMR) in magnetic tunnel junction with embedded nano-particles (npMTJ). The simulation is done in the range of coherent electron tunneling model through the insulating layer with embedded magnetic and non-magnetic nano-particles (NPs). We consider two conduction channels in parallel within one MTJ cell, in which one is through double barriers with NP (path I in Fig. 1) and another is through a single barrier (path II). The model allows us to reproduce the TMR dependencies at low temperatures of the experimental results for npMTJs [2-4] having in-plane magnetic anisotropy. In our model we can reproduce the anomalous bias-dependence of TMR and enhanced TMR with magnetic and non-magnetic NPs. We found that the electron transport through NPs is similar to coherent one for double barrier magnetic tunnel junction (DMTJ) [1]; therefore, we take into account all transmitting electron trajectories and the spin-dependent momentum conservation law in a similar way as for DMTJs. The formula of the conductance for parallel (P) and anti-parallel (AP) magnetic configurations is presented as following: GsP(AP) = G0σk F, s2/4π ∫ Cos (θs) DsP(AP) Sin(θ)dθsd, where Cos(θs) is cosine of incidence angle of the electron trajectory θs, with spin index s=(↑,↓), kF, s, is the Fermi wave-vector of the top (bottom) ferromagnetic layers; for simplicity the top and bottom ferromagnetic layers are taken as symmetric; G0=2e2/h and σ is area of the tunneling cell. The transmission probability DsP(AP) depends on diameter of NP (d), effective mass m and wave-vector of the electron kNP attributing to the quantum state on NP (corresponding to the k-vector of the middle layer in DMTJs [1], and which is affected by applied bias V). Furthermore DsP(AP) depends on Cos(θs), kF, s, barriers heights U1,2 and widths L1,2, respectively. The exact quantum mechanical solution for symmetric DMTJ was found in Ref.[1]. Here we employ parallel circuit connection of the tunneling unit cells, where each cell contains one NP with the average d less than 3 nm per unit cell's area (σ =20 nm2), while tunnel junction itself has surface area S and consists of N cells (N=S/σ). The total conductance of the junction is G = Nx (G1↑+G2↑+G1↓+G2↓), where G1, s is dominant conductance with the NP (path I), G2, s is conductance of the direct tunneling through the single barrier (path II), and TMR=(GP-GAP)/GAP ×100%

Calculation of Tunnel Magnetoresistance in Magnetic Tunnel Junctions with Particle Size Dispersion

© 2010-2012 IEEE.Simulation results are given for electron tunneling through the insulating layer of a magnetic tunnel junction with embedded nonmagnetic nanoparticles (NPs). The size dispersion of the NPs was an important part of the solution for tunnel magnetoresistance, which was calculated on the basis of the double-barrier model. Theoretical agreement with experimental data was achieved by adjusting the NP dispersion and quantization. A step-like quantization related to the initial distribution of the electrons over quantum-well states was considered for different size NPs

The calculation of parameters and designe of «Plasma focus» facility

In this paper, the plasma focus type devices are seen as an alternative to traditional magnetic systems and laser fusion. The authors present the researches results of plasma formation on the ”CPA-30” plasma accelerator and plasma installation “Focus fusion”..