Itinerant ferromagnetism in the As 4$p$ conduction band of Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ identified by x-ray magnetic circular dichroism

TL;DR

This study demonstrates that ferromagnetism in Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ originates from the As 4p conduction band, revealing coexistence of local-moment antiferromagnetism and itinerant ferromagnetism with distinct easy axes.

Contribution

It identifies the As 4p conduction band as the origin of itinerant ferromagnetism in Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ using XMCD measurements, highlighting coexistence of magnetic orders.

Findings

Ferromagnetism arises in the As 4p conduction band.

No XMCD signal at Mn edges, indicating no local Mn moment contribution.

Orbital magnetic moment lies in the basal plane.

Abstract

X-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ show that the ferromagnetism below $T_{\textrm{C}}\approx$ 100 K arises in the As $4p$ conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below $T_{\textrm{C}}$, however, a clear XMCD signal is found at the As $K$ edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic $\textrm{c}$ axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As $4p$ conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.