Piezomagnetism-driven magnetoelectric coupling in altermagnetic multiferroic K3Cr2F7

TL;DR

This paper demonstrates how Jahn-Teller distortions and oxygen octahedral rotations induce multiferroicity and control altermagnetic spin order in K3Cr2F7, enabling strong magnetoelectric coupling and functional tunability.

Contribution

It introduces a design rule linking lattice distortions to multiferroicity in halide compounds, revealing control of altermagnetism in real space.

Findings

Jahn-Teller distortion cooperates with octahedral rotations to break inversion symmetry.

Altermagnetic order transforms into antiferromagnetic order across phase transition.

Strain/pressure can modulate weak ferromagnetism in K3Cr2F7.

Abstract

Ferroelectric control of altermagnetism in momentum space has been studied widely, while the control of magnetism in real space of altermagnets are still rare. We present a design rule to identify multiferroicity in n=2 Ruddlesden-Popper halides. Our results show that a Jahn-Teller distortion can cooperate with oxygen octahedral rotations to break inversion symmetry, which we demonstrate in K3Cr2F7 and cation-ordered KAg2Cu2Cl7, and leads to a ferrielectric-to-ferroelectric phase transition in K3Cr2F7. Altermagnetic spin order in the ferrielectric phase of K3Cr2F7 transforms into a conventional antiferromagnetic order in the ferroelectric phase, at which strain/pressure engineered sizable changes of weak ferromagnetism can occur. Our study is not only conducive to realize strong magnetoelectric coupling in multiferroics, but also reveals more functionalities in altermagnetic materials.