Gap state charge induced spin-dependent negative differential resistance in tunnel junctions

TL;DR

This paper introduces a novel spin-dependent negative differential resistance mechanism in magnetic tunnel junctions using cubic cation disordered crystals, enabling electric control of spin transport in spintronic devices.

Contribution

It proposes and demonstrates a new NDR mechanism based on arched band gaps induced by cation doping in ultrathin tunnel junctions, supported by first-principles calculations.

Findings

NDR can be achieved in either spin channel with appropriate bias.

The mechanism applies to 2D and 3D ultrathin junctions with small band gaps.

A generalized tunneling formula explains conditions for NDR occurrence.

Abstract

We propose and demonstrate through first-principles calculation a new spin-dependent negative differential resistance (NDR) mechanism in magnetic tunnel junctions (MTJ) with cubic cation disordered crystals (CCDC) AlO$_x$ or Mg$_{1-x}$Al$_x$O as barrier materials. The CCDC is a class of insulators whose band gap can be changed by cation doping. The gap becomes arched in an ultrathin layer due to the space charge formed from metal-induced gap states. With an appropriate combination of an arched gap and a bias voltage, NDR can be produced in either spin channel. This mechanism is applicable to 2D and 3D ultrathin junctions with a sufficiently small band gap that forms a large space charge. It provides a new way of controlling the spin-dependent transport in spintronic devices by an electric field. A generalized Simmons formula for tunneling current through junction with an arched gap is derived to show the general conditions under which ultrathin junctions may exhibit NDR.