Search

This study demonstrates a mathematical description of a point-like nanocontact model, which is developed to simulate electron transport through a nanoconstriction between magnetic or non-magnetic contact sides. The theory represents a solution to the quasi-(semi)-classical transport equations for charge current, which takes into account second-order derivatives of the related quasi-classical Green functions along the transport direction. The theoretical approach also enables the creation of an I-V model for a heterojunction with embedded objects, where the initial condition, a conduction band minimum profile of the system, is well-defined. The presented spin-resolved current approach covers a complete range of the scales including quantum, ballistic, quasi-ballistic (intermediate), and diffusive classical transport conditions, with a smooth transition between them without residual terms or any empirical variables. The main benefit of the mathematical solution is its novel methodology, which is an alternative candidate to the well-known Boltzmann technique.

The work represents the theoretical modeling of the electrical conductance in the nanoscale interconnects within approach of the extended point-like contact (PC) model. The approach describes a diffusive, quasi-ballistic, ballistic and quantum regimes of the spinresolved conductance, that is important for the development of the heterojunction models, including 2D -3D interconnects. As a benefit, the model provides a unified description of the contact resistance from Maxwell diffusive through the ballistic to a purely quantum transport regimes without residual terms. The model of the PC assumes that the contact area can be replaced by a complex quantum device, e.g. single tunnel junction, narrow magnetic domain wall (DW), vacuum gap between tip and surface, source to drain transistor’s channel, etc. The potential energy landscape of the device determines its electrical properties.

The work represents the extended theoretical model of the electrical conductance in nanoscale magnetic point-like contacts. The developed approach describes diffusive, quasi-ballistic, ballistic and quantum regimes of the spin-resolved conductance that is important for further development of the contact Andreev reflection spectroscopy, heterojunction models, scanning tunnel microscopy techniques. As a benefit, the model provides a unified description of the contact resistance from Maxwell diffusive through the ballistic to purely quantum transport regimes without residual terms. The model of the point contact assumes that the contact area can be replaced by a complicated object (i.e. the tunnel barrier or complicated one with nanoparticles, narrow domain wall, etc.), where the potential energy profile determines its electrical properties. The model can be easily adapted to particular contact materials, its physical properties and species of the contact area.

The theoretical model of spin-dependent transport in magnetic tunnel junctions (MTJ) containing magnetic or non-magnetic nanoparticle is developed. The dependences of tunnel magnetoresistance (TMR) and in-plane component of spin transfer torque (STT) on the applied voltage for various sizes of nanoparticles of the order of the mean free path of the conduction electron are calculated. The calculation is performed in the approximation of the ballistic transport of conduction electrons through the insulating layers of the MTJ and the nanoparticles.

Various multilayer systems such as magnetic tunnel junctions and their modifications attract attention due to their promising applications: magnetic field sensors, magnetic memory, memristors, nano spin-valves, and resistance generators. The current progress in studying giant magnetoresistance, tunnel magnetoresistance, and spin-transfer torque (STT) can provide successful solutions of the problems related to energy consumption and thermal stability factor of magnetic random access memory (MRAM, STT MRAM). Moreover, spintronic devices have a unique advantage against semiconductor devices that they are nonvolatile. In addition, they are expected to be more scalable than semiconductor-based devices, because magnetic nano-domain is much more stable groundwork for the information storage in contrast to a charged micro-capacitor. It is well-known that the leakage current rapidly increases with a capacitor dimension reduced down to the nano-scale.

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 simulation is done for electron tunneling through the insulating layer of the magnetic tunnel junction with non-magnetic embedded nanoparticles (npMTJs). The distribution of the nanoparticles by size (DNPS) was important part of the solution for tunnel magnetoresistance (TMR) which was calculated on the basement of the double barrier tunneling model. It was found that theoretical agreement with experimental data can be influenced not only from DNPS but also due to different cases of the quantization. A few cases of the quantization related with a redistribution over quantum well (QW) states of the nanoparticles (NPs) (with diameter d) were considered (one of the possible DNPS and related TMR is shown in Fig. 1a and Fig. 1b).

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 nonmagnetic 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 literature., Comment: 9 pages, 6 figures

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.

The objective of this work is to describe the tunnel electron current in single barrier magnetic tunnel junctions within a new approach that goes beyond the single-band transport model. We propose a ballistic multi-channel 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/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ tunnel junctions, where the electronic band structures of Fe and La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ are derived by \it{ab-initio} calculations.

Resonant tunneling is studied theoretically for the planar asymmetrical double-barrier magnetic tunnel junction (DMTJ) when a dc bias field is applied. The spin-polarized conductance and tunnel magnetoresistance (TMR) through the DMTJ have been calculated. In DMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. Analytical expression for the transmission coefficient of the DMTJ is received, which is expressed through the single-barrier transmission coefficients taking into account the voltage drop on each barrier and spin degrees of freedom of the electron. The dependencies of the tunnel conductance and TMR on the applied voltage have been calculated for the case of resonant transmission.