Symmetry analysis of complex magnetic structure in monoclinically distorted Er3Cu4Sn4

The magnetic structure in Er 3 Cu 4 Sn 4 has been determined using high-resolution powder neutron diffraction, supported by symmetry analysis. At low temperatures, Er 3 Cu 4 Sn 4 assumes a crystal structure of the Tm 3 Cu 4 Sn 4 type (in the monoclinic space group C 2/ m ). The Er atoms occupy two distinct Wyckoff sites: 2 c and 4 i . It has been found that the Er magnetic moments on the 2 c site form a commensurate antiferromagnetic structure ( k 1 = [0, 0, ½]) below 6 K. The magnetic moments reach 8.91 (8) μ B at 1.4 K and are parallel to the b axis. The Er magnetic moments on the 4 i site order below 2 K and form an incommensurate antiferromagnetic sine-modulated structure ( k 2 = [1, 0.4667 (1), ½]), with magnetic moments lying in the ac plane and perpendicular to the a axis. The amplitude of modulation equals 8.7 (1) μ B at 1.4 K.