The incommensurate magnetic structure of Er3Cu4Ge4below 1 K

The magnetic structure of Er3Cu4Ge4 was previously studied down to 1.5 K by Wawrzynska et al. who found that the Er(2d) sublattice orders at 8 K in a commensurate, doubled structure (kd = [0 1/2 0]) with an Er moment close to the free-ion value of 9 μB. By contrast, the Er(4e) sublattice ordered at 3.5 K in an incommensurate structure (ke = [0 0.883(2) 0]) with a greatly reduced moment (about one-third of the free-ion value). We have extended this study by high-resolution neutron powder diffraction down to 0.34 K in an effort to establish if the Er(4e) sublattice eventually locks-in and attains its free-ion moment (in keeping with our 166Er Moessbauer work). We observed a change in the Er(4e) order, beginning at 1.4 K, leading to a magnetic structure at 0.34 K which has almost locked-in but with (ke = [0.1 2/3 0]) and a still-reduced Er moment.