New insight into tuning magnetic phases of $R$Mn$_6$Sn$_6$ kagome metals

TL;DR

This study investigates the magnetic phases of ErMn$_6$Sn$_6$, revealing how thermal fluctuations influence magnetic order and offering insights into controlling Dirac fermions in kagome metals.

Contribution

The paper combines neutron diffraction and mean-field analysis to predict multiple temperature and field-dependent magnetic phases in ErMn$_6$Sn$_6$, highlighting the role of thermal fluctuations.

Findings

ErMn$_6$Sn$_6$ is near a boundary between spiral and ferrimagnetic states.

Thermal fluctuations weaken Mn-Er interactions and affect phase stability.

Multiple magnetic phases can be controlled by temperature and magnetic field.

Abstract

Predicting magnetic ordering in kagome compounds offers the possibility of harnessing topological or flat-band physical properties through tuning of the magnetism. Here, we examine the magnetic interactions and phases of ErMn$_6$Sn$_6$ which belongs to a family of $R$Mn$_6$Sn$_6$, $R=$ Sc, Y, Gd--Lu, compounds with magnetic kagome Mn layers, triangular $R$ layers, and signatures of topological properties. Using results from single-crystal neutron diffraction and mean-field analysis, we find that ErMn$_6$Sn$_6$ sits close to the critical boundary separating the spiral-magnetic and ferrimagnetic ordered states typical for nonmagnetic versus magnetic $R$ layers, respectively. Finding interlayer magnetic interactions and easy-plane Mn magnetic anisotropy consistent with other members of the family, we predict the existence of a number of temperature and field dependent collinear, noncollinear, and noncoplanar magnetic phases. We show that thermal fluctuations of the Er magnetic moment, which act to weaken the Mn-Er interlayer magnetic interaction and quench the Er magnetic anisotropy, dictate magnetic phase stability. Our results provide a starting point and outline a multitude of possibilities for studying the behavior of Dirac fermions in $R$Mn$_6$Sn$_6$ compounds with control of the Mn spin orientation and real-space spin chirality.