Giant Rashba electrical control of magnetism in band models

TL;DR

This paper demonstrates that Rashba spin-orbit coupling, enhanced by a periodic potential, can enable giant, electrically controllable perpendicular magnetic anisotropy with low dissipation, offering a new approach to magnetism control.

Contribution

It introduces a novel theoretical model showing how Rashba effects combined with periodic potentials can produce giant, linear electric field-controlled magnetic anisotropy in band models.

Findings

Rashba PMA is enhanced by 2-3 orders of magnitude with a periodic potential.

Electrical control of band-structure gaps linear in electric field is predicted.

Low dissipation electric field-driven magnetic dynamics are possible.

Abstract

It is of considerable technological importance to achieve an electrical control of magnetism of sufficient magnitude. To overcome the in-plane shape anisotropy, needed is the electrical control of a perpendicular magnetic anisotropy (PMA). It is known, within a free electron model, the Rashba spin-orbit coupling provides such a control. Surprisingly, this same Rashba PMA is enhanced by two to three orders of magnitude when a periodic potential is added. Usually spin Berry phase physics reflects time dependent magnetic fields. Here it is shown, within a time independent model, such physics arises because the Rashba effective magnetic field has texture within the unit cell. Predicted are electrical controllable band-structure gaps, linear in the applied electric field $E$, that can result in a truly giant linear PMA. Also possible is a Peierls mechanism, in which the magnetisation tilts from the vertical, shifting these gaps to the Fermi level. As a consequence there are low dissipation electric field driven dynamics, an alternative to the more dissipative spin torque transfer (STT) effect. The theory requires the introduction of an intrinsic spin Berry connection $\vec A_s$, an effective vector potential, and is incompatible with current density functional theories (DFT).