Effect of symmetry reduction on the magnetic properties of LnIr$_2$Si$_2$ polymorphs

TL;DR

This study investigates how different crystal symmetries in LnIr$_2$Si$_2$ polymorphs influence their magnetic ordering temperatures and moment orientations, revealing significant effects of structural symmetry on magnetic properties.

Contribution

It provides a comparative analysis of magnetic properties in polymorphs with different symmetries, highlighting the impact of crystal structure on magnetic behavior in LnIr$_2$Si$_2$ compounds.

Findings

Higher symmetry phase orders antiferromagnetically at 87 K

Lower symmetry phase orders at 12 K

Magnetic moments lie in the a-a plane in both polymorphs

Abstract

Many tetragonal compounds LnIr$_2$Si$_2$ (Ln = lanthanoid) occur in two polymorphous phases and are therefore well suited to study the relationship between crystal structure and magnetic properties. We have grown GdIr$_2$Si$_2$ single crystals of both polymorphs from a high-temperature indium flux and investigated their anisotropic magnetic properties. The higher symmetric form with the ThCr$_2$Si$_2$ structure (space group $I4/mmm$) orders antiferromagnetically at $T_{\rm N}=87\,\rm K$ while for the lower symmetric compound in the CaBe$_2$Ge$_2$ structure (space group $P4/nmm$) we determined a much lower \neel temperature $T_{\rm N}=12\,\rm K$. Our magnetic characterization of the single crystals reveals that for both compounds the magnetic moments are aligned in the $a-a$ plane of the tetragonal lattice, but that the change of the symmetry strongly effects the inplane alignment of the moment orientation. For Ln$=$Er and Ho, we confirmed the existence of LnIr$_2$Si$_2$ in the space group $P4/nmm$. The magnetic properties of these lower symmetric compounds are in remarkable difference to their related compounds in the space group $I4/mmm$.