Gadolinium: a helical antiferromagnet or a collinear ferromagnet

Contrary to the recent claim that gadolinium behaves as an antiferromagnet with a helical spin structure for temperatures between the spin reorientation (SR) temperature TSR and the Neel point, the ac susceptibility and low-field bulk magnetization data taken along the [0001] and [101- 0] hexagonal directions of high-purity gadolinium single crystals over a wide range of temperatures provide ample experimental evidence in favor of the widely accepted view that gadolinium is a normal ferromagnet with a collinear spin structure in the temperature range from TSR to the Curie point TC. However, the magnetic behavior of gadolinium is complicated by a rather complex temperature dependence of the easy direction of magnetization for temperatures below TSR