Cycloidal Magnetic Ordering in Noncentrosymmetric EuIrGe$_3$

TL;DR

This study uncovers complex cycloidal magnetic orderings in EuIrGe3 across multiple phases, revealing incommensurate and cycloidal structures influenced by the compound's noncentrosymmetric polar environment.

Contribution

It provides detailed neutron and resonant X-ray diffraction analysis of successive magnetic phases and highlights the role of odd-parity magnetic quadrupole interference in EuIrGe3.

Findings

Incommensurate sinusoidal order with q~(0,0,0.792) in high-temperature phase.

Cycloidal order with q=(δ',0,0.8) in intermediate phase.

Cycloidal plane rotation by 45° in low-temperature phase.

Abstract

Successive magnetic phase transitions at $T_{\text{N}}$=12.2 K, $T_{\text{N}}^{\;\prime}$=7.0 K, and $T_{\text{N}}^{\;*}$=5.0 K in EuIrGe$_3$, an intermetallic compound with a body centered tetragonal lattice belonging to a polar space group $I4mm$, has been investigated by neutron diffraction and resonant X-ray diffraction. It is shown that EuIrGe$_3$ exhibits an incommensurate longitudinal sinusoidal order with $q\sim (0, 0, 0.792)$ and $m_{q} \parallel c\text{-axis}$ in the high temperature phase ($T_{\text{N}}^{\;\prime}< T < T_{\text{N}}$), which changes to a cycloidal order with $q=(\delta', 0, 0.8)$ ($\delta'\sim 0.017$) and $m_{q} \parallel ac\text{-plane}$ in the intermediate phase ($T_{\text{N}}^{\;*} < T < T_{\text{N}}^{\;\prime}$). In the low temperature phase ($T < T_{\text{N}}^{\;*}$), the cycloidal plane rotates by $45^{\circ}$ to have $q=(\delta, \delta, 0.8)$ ($\delta\sim 0.012$). It is also pointed out that the X-ray scattering amplitude from odd-parity magnetic quadrupole due to the polar environment interfere with that from normal even-parity magnetic dipole in the magnetic ordered phase.