Augmented Magnetic Octupole in Kagome Antiferromagnets Detectable via X-ray Magnetic Circular Dichroism

TL;DR

This paper reveals that X-ray magnetic circular dichroism can detect an augmented magnetic octupole in Kagome antiferromagnets, providing a new method to analyze multipole moments despite zero net magnetization.

Contribution

It demonstrates that XMCD from the magnetic dipole operator can reveal multipole moments like the augmented magnetic octupole in antiferromagnets with broken TRS.

Findings

XMCD from the Sz term is negligible in Kagome AFMs.

The Tz term in XMCD remains uncancelled and linked to the augmented magnetic octupole.

XMCD can effectively analyze multipole moments in antiferromagnets.

Abstract

The magneto-optical Kerr effect (MOKE) has recently been discovered in antiferromagnetic Kagome lattice Mn3Sn. Since the compound exhibits a coplanar $120^\circ$ antiferromagnetic (AFM) order, the magnetic moments cancel each other, and the net magnetization is almost zero. However, the MOKE is allowed due to the lack of the time-reversal symmetry (TRS) of the AFM order. X-ray magnetic circular dichroism (XMCD) can detect a difference in up and down the spin density of states (DOS), and thus XMCD originating from the spin operator, the so-called Sz term, should be negligibly small as well as the net magnetization. Nonetheless, we show that XMCD originating from the magnetic dipole operator, the so-called Tz term, should remain uncancelled in the AFM with the broken TRS. Moreover, we clarify that there is a strong link between the Tz term and the augmented magnetic octupole (AMO), which suggests that XMCD can be an effective approach for analyzing multipole moments in antiferromagnets.