Confirmation of complex non-collinear Fe(II) spin ordering in the iron oxychalcogenide La 2 O 2 Fe 2 OSe 2 by broad range 139 La-NQR

The transition metal oxychalcogenide La 2 O 2 Fe 2 OSe 2 exhibits a non-collinear spin-ice like antiferromagnetic ordering below T N about 90 K due to complex magnetic exchange interactions and axial single-ion anisotropy of Fe 2+ spins. The magnetic structure was deduced/determined from combined 57 Fe Mössbauer spectroscopy and 139 La-NMR on polycrystalline specimen. In this work, we present zero-field 139 La-NQR investigations on polycrystalline La 2 O 2 Fe 2 OSe 2 in a broad frequency and temperature range between 2.8 - 20 MHz and 4.2 - 100 K. The measured resonances at ν Q, 2, ν Q, and 3, ν Q are fully consistent with the previous NMR studies and also with the magnetic structure. A substantial modification of the electric field gradient at the La-position below T N is inconsistent with the current investigations.