Cycloidal Magnetic Ordering in Noncentrosymmetric EuIrGe3

Abstract

Successive magnetic phase transitions at TN = 12.2 K, \(T'_{\text{N}} = 7.0\) K, and \(T_{\text{N}}^{*} = 5.0\) K in EuIrGe3, 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 EuIrGe3 exhibits an incommensurate longitudinal sinusoidal order with \(\boldsymbol{q} \sim (0,0,0.792)\) and mq || c-axis in the high temperature phase (\(T'_{\text{N}} < T < T_{\text{N}}\)), which changes to a cycloidal order with \(\boldsymbol{q} = (\delta ',0,0.8)\) (δ′ ∼ 0.017) and mq || ac-plane in the intermediate phase (\(T_{\text{N}}^{*} < T < T'_{\text{N}}\)). In the low temperature phase (\(T < T_{\text{N}}^{*}\)), the cycloidal plane rotates by 45° to have \(\boldsymbol{q} = (\delta ,\delta ,0.8)\) (δ ∼ 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.