Persistent altermagnetism

TL;DR

This paper introduces persistent altermagnetic spin polarization (PASP), a robust collinear spin polarization protected by symmetry and exchange order, promising for spintronics and magnetic memory applications.

Contribution

It identifies a new class of spin polarization, PASP, protected by mirror symmetry and exchange order, in various materials and classifies its universal principles in spin-orbit-coupled monolayers.

Findings

PASP occurs in 158 spin layer groups and specific materials.

PASP is ferroelectrically switchable in VSI$_2$.

Switching PASP significantly alters spin-filtering conductance.

Abstract

Persistent spin textures with collinear spin polarization are promising platforms for spintronics applications. However, their typically relativistic spin-orbit origin leads to weak spin splittings and fragile spin coherence. Here, we demonstrate a previously overlooked class of robust collinear spin polarization protected by mirror symmetry in combination with a strong exchange-driven altermagnetic order, which persists even in the presence of spin-orbit coupling. By combining first-principles calculations with a systematic classification of spin and magnetic layer groups, we identify this phenomenon-termed persistent altermagnetic spin polarization (PASP)-to occur in 158 spin layer groups and in representative materials including metallic V$_2$Te$_2$O, insulating La$_2$CuO$_4$, and semiconducting VSI$_2$. Furthermore, we theoretically demonstrate that PASP is ferroelectrically switchable in VSI$_2$. Finally, we show that this PASP switching can lead to large changes in spin-filtering conductance in a model all-altermagnetic junction. Our results open the possibility of employing PASP in all-altermagnetic magnetic memory and spin-transistor devices and establish universal principles of altermagnetism in spin-orbit-coupled monolayers.