The magnetic structure of Er 2MgGe 2

Abstract

A series of Mg-based germanides, R_2MgGe_2 have been synthesized with the heavy R elements. They crystallize in the tetragonal Mo_2FeB_2-type structure with the P4/mbm space group. The R_2MgGe_2 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 Er_2MgGe_2 and Tm_2MgGe_2, down to 5 K. Electronic structure calculations on Gd_2MgGe_2 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 Er_2MgGe_2 to search for magnetic order and to determine the magnetic structure if order is indeed observed. We find that Er_2MgGe_2 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.