The magnetic structures of YbMn2Si2

The magnetic structures of YbMn2Si2 with the tetragonal ThCr2Si2-type struc ture have been determined by neutron diffraction measurements over the temp erature range similar to1.5-538 K. Rietveld refinements demonstrate that Yb Mn2Si2 has a collinear antiferromagnetic structure below the Neel temperatu re T-N1 = 526(4) K with the Mn moments parallel to the c-axis. Below T-N2 s imilar to 30(5) K, the Mn sublattice rearranges to a +--+ antiferromagnetic structure with propagation vector k = 00(1)/(2). The moment direction is a long the c-axis with a total moment of 1.92(8) mu (B) at 10 K. There is no indication of ordering of the Yb ions at 10 K, although a diffraction patte rn at 1.5 K shows that the Yb ions are ordered at the latter temperature. A nalysis reveals that the Yb sublattice orders antiferromagnetically. The an tiferromagnetically ordered Yb sublattice exhibits the same propagation vec tor, k = 00(1)/(2), as the Mn sublattice, although the Yb spin directions a re found to be perpendicular to the c-axis compared with the parallel align ment of the Mn moments. The refined value of the Yb3+ magnetic moment at 1. 5 K is mu (Yb) = 0.57(9) mu (B) compared with the free ion value of about 4 .5 AB, while at 1.5 K the Mn magnetic moment is mu (Mn) = 1.98(7) mu (B).