Magnetic structure of Y_{1 - x} Nd_x Mn₆ Sn₆ alloys

We have made magnetization measurements and neutron diffraction experiments on Y_{1 - x} Nd_x Mn₆ Sn₆ alloys (0 ≤ x ≤ 0.5) with hp13-type structure. The alloy with x = 0.2 shows a hexagonal structure with the lattice constants of a = 5.515 Å and c = 8.990 Å and a helical antiferromagnetic structure with propagation vector q = (0, 0, frac(1, 6)) under a magnetic field H = 0 at 10 K. The helical magnetic arrangement is easily destroyed by applied magnetic field, and becomes finally, a simple ferromagnetic arrangement in a field of 5.5 T. The alloy with x = 0.4 shows a simple ferromagnetic structure even H = 0 at 10 K. It is likely that the magnetic moments of Mn and Nd atoms are 2.3 μ_B / Mn atom and 3.2 μ_B / Nd atom, lay in the c-plane, and keep a constant values at 10 K in the whole composition (0 < x ≤ 0.5).