On the magnetic order of Gd5Ge3.

We have investigated the magnetic structure of Gd₅Ge₃ by neutron powder diffraction down to 3.6K. This compound presents three events in the heat capacity which we show are related to fundamental changes in the magnetic order. The primary antiferromagnetic ordering occurs at 82(2) K and produces a magnetic cell that is tripled with respect to the underlying orthorhombic crystal cell. The propagation vector is k₁ = [00 1/3]. At 74(2) K, the magnetic order becomes "anti-C" with a propagation vector k₂ = [1 0 0]. A third change in the magnetic order occurs at 40(2) K, and the new magnetic structure is essentially the "anti-C" structure but with the addition of a tripled magnetic component corresponding to a propagation vector k₃ = [1/3 0 0]. [ABSTRACT FROM AUTHOR]