Unique magnetic structure of YbCo$_2$Si$_2$

TL;DR

This study reveals two distinct magnetic phases in YbCo$_2$Si$_2$ below 1.7 K, with a commensurate structure at the lowest temperatures and an incommensurate one at intermediate temperatures, likely due to Yb 4f electron itineracy.

Contribution

First detailed neutron diffraction analysis of YbCo$_2$Si$_2$ revealing unique magnetic structures distinct from other RCo$_2$Si$_2$ compounds.

Findings

Low-temperature phase has commensurate magnetic order with k1 = (0.25, 0.25, 1)

Intermediate phase exhibits incommensurate order with k2 = (0.25, 0.086, 1)

Magnetic structure likely influenced by Yb 4f electron itineracy

Abstract

We report on the results of powder and single crystal neutron diffraction to investigate the magnetic order in YbCo$_2$Si$_2$ below the N\'eel temperature $T_{\rm N} = 1.7~$K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector ${\bf k}_1 = (0.25~ 0.25~ 1)$ is found, while the intermediate phase ($T > 0.9~$K) is characterized by an incommensurate magnetic structure with ${\bf k}_2 = (0.25~ 0.086~ 1)$. The magnetic structure in YbCo$_2$Si$_2$ is in marked contrast to all other known RCo$_2$Si$_2$ compounds (R = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.