arXiv subjects

Andrey Umerski

Publications and source records attributed to Andrey Umerski.

3 recordsLinked to original sources

arXiv2026

Bias controlled Interlayer Exchange Coupling

We demonstrate, using computer simulations and a non-equilibrium Greens function approach, that the sign of the out-of-equilibrium interlayer exchange coupling (ooeIEC) can change in the presence of an externally applied electrical bias. Our system consists of an insulating section connected to an exchange coupled ferromagnetic (FM) tri-layer, sandwiched between semi-infinite leads. When the exchange coupled trilayer contains a quantum-well state confined in the hybridisation gap (HG) of the FM, we find that a relatively small applied electrical bias can switch the lowest energy state of the tri-layer between parallel (P) and anti-parallel (AP) configurations. We consider three cases for the insulating section; a single tunnelling barrier, a resonant tunnelling barrier and an amorphous insulating barrier and, in each case, show that the bias dependence of the ooeIEC is strongly dependent on the system conductance. We find that the lowest switching current densities are achieved with strongly confined quantum well states.

cond-mat.mes-hall↗

arXiv2024

Application of the Landauer-Büttiker method to the calculation of interlayer exchange coupling in closed ballistic multi-layers

In this communication we study the behaviour of spin current components in a ballistic junction consisting of two semi-infinite leads and a scattering region composed of two magnetic layers separated by a non-magnetic metallic spacer. We then consider the system being gradually isolated from the leads, which we refer to as the transition from an open to a closed regime. As expected on physical grounds, charge and in-plane components vanish, but the out-of-plane spin current remains finite and gives rise to the oscillatory interlayer exchange coupling (IEC) between the magnets. We show that the out-of-plane spin current reduces to a set of peaks in momentum space, which correspond to discrete energy eigenstates of the closed system. Furthermore, we demonstrate that the expression for the IEC in terms of spin current for an open system reduces to an expression in the closed system, which corresponds exactly to the definition of IEC in terms of energy difference.

cond-mat.mes-hall↗

arXiv2019

Application of the Landauer formalism to the calculation of spin current

In this communication we apply the Landauer method and transfer matrix formalism to the calculation of spin current in magnetic multilayered structures within a ballistic quantum-mechanical regime. The method provides an elegant and intuitive formalism with which to study spin current properties and within which closed-form expressions with a transparent physical interpretation can be obtained. We apply the method to illuminate origin and the symmetry properties of the various spin current components within the parabolic band approximation. We also apply the stationary phase approximation to develop asymptotic approximations to the total spin current within this formalism, and show that these give excellent agreement with full numerical calculations for both barrier and well systems.

cond-mat.mes-hall↗