Structural distortion and incommensurate noncollinear magnetism in EuAg4As2

TL;DR

This study uncovers structural distortion and complex noncollinear magnetic ordering in EuAg4As2, revealing rich magnetic phases, significant magnetoresistance, and strong charge-magnetism coupling in this layered pnictide.

Contribution

It reports the first observation of structural distortion and incommensurate noncollinear magnetism in EuAg4As2, expanding understanding of magnetic phenomena in layered pnictides.

Findings

Structural distortion at 120 K with superlattice peaks

Incommensurate noncollinear antiferromagnetic order below 9 K

Rich magnetic phases and large magnetoresistance

Abstract

Layered pnictide materials have provided a fruitful platform to study various emergent phenomena, including superconductivity, magnetism, charge density waves, etc. Here we report the observation of structural distortion and noncollinear magnetism in layered pnictide EuAg$_4$As$_2$ via transport, magnetization, single crystal X-ray and neutron diffraction data. EuAg$_4$As$_2$ single crystal shows a structural distortion at 120 K, where two sets of superlattice peaks with the propagation vectors of $q_1=\pm$(0, 0.25, 0.5) and $q_2=\pm$(0.25, 0, 1) emerge. Between 9 K to 15 K, the hexagonal Eu$^{2+}$ sub-lattice enters an unpinned state, with magnetic Bragg reflections pictured as circular-sectors. Below 9 K, it orders in an incommensurate noncollinear antiferromagnetic state with a well-defined propagation wavevector of (0, 0.1, 0.12), where the magnetic structure is helical along the $c$ axis and cycloidal along the $b$ axis with a moment of 6.4 $\mu_B$/Eu$^{2+}$. Furthermore, rich magnetic phases under magnetic fields, large magnetoresistance, and strong coupling between charge carriers and magnetism in EuAg$_4$As$_2$ are revealed.