Long-range magnetic order in CePdAl$_3$ enabled by orthorhombic deformation

TL;DR

This study demonstrates that orthorhombic deformation in CePdAl$_3$ relieves magnetic frustration, enabling long-range antiferromagnetic order that is absent in the tetragonal form, with detailed structural and magnetic characterizations.

Contribution

It reveals how structural deformation from tetragonal to orthorhombic in CePdAl$_3$ enables long-range magnetic order by relieving magnetic frustration, supported by diffraction and spectroscopic data.

Findings

Orthorhombic CePdAl$_3$ exhibits long-range antiferromagnetic order below 5.29 K.

Structural deformation reduces magnetic frustration present in the tetragonal phase.

Strong spin-orbit coupling influences magnetic anisotropies in orthorhombic CePdAl$_3$.

Abstract

We investigate the effect of structural deformation on the magnetic properties of orthorhombic CePdAl$_3$ in relation to its tetragonal polymorph. Utilizing x-ray and neutron diffraction we establish that the crystal structure has the $Cmcm$ space group symmetry and exhibits pseudo-tetragonal twinning. According to density-functional calculations the tetragonal-orthorhombic deformation mechanism has its grounds in relatively small free enthalpy difference between the polymorphs, allowing either phase to be quenched and fully accounts for the twinned microstructure of the orthorhombic phase. Neutron diffraction measurements show that orthorhombic CePdAl$_3$ establishes long-range magnetic order below $T_\mathrm{N}$=5.29 (5) K characterized by a collinear, antiferromagnetic arrangement of magnetic moments. Magnetic anisotropies of orthorhombic CePdAl$_3$ arise from strong spin-orbit coupling as evidenced by the crystal-field splitting of the $4f$ multiplet, fully characterised with neutron spectroscopy. We discuss the potential mechanism of frustration posed by antiferromagnetic interactions between nearest neighbours in the tetragonal phase, which hinders the formation of long-range magnetic order in tetragonal CePdAl$_3$. We propose that orthorhombic deformation releases the frustration and allows for long-range magnetic order.