The magnetic structure of Er₂MgGe₂

A series of Mg-based germanides, R₂MgGe₂ have been synthesized with the heavy R elements. They crystallize in the tetragonal Mo₂FeB₂-type structure with the P4/mbm space group. The R₂MgGe₂ compounds are antiferromagnets with Neel temperatures ranging from 150 K (R = Gd) to 13 K (R = Sm). However, no sign of magnetic order has been observed for Er₂MgGe₂ and Tm₂MgGe₂, down to 5 K. Electronic structure calculations on Gd₂MgGe₂ suggest that the magnetic order of tnese compounds might be more complex than a simple collinear antiferromagnetism. In this report, we present our neutron diffraction studies of Er₂MgGe₂ to search for magnetic order and to determine the magnetic structure if order is indeed observed. We find that Er₂MgGe₂ orders antiferromagnetically at ~4 K. At 3 K, the magnetic structure can be described by a propagation vector of k = [¹/₂, ¹/₂, ¹/₄], with the Er magnetic moments forming a non-collinear antiferromagnetic structure with an intermediate planar arrangement.