Magnetic Structure of TbAg2

Neutron‐diffraction measurements have revealed that TbAg₂ having the tetragonal CaC₂‐type structure becomes antiferromagnetic below the Néel temperature of 35°K. The ordered magnetic structure consists of the ferromagnetic sheets which are perpendicular to the $a$ axis (face‐centered description), and the moment directions of the adjacent ferromagnetic sheets are opposite to one another. All moments are aligned in the direction of the $c$ axis, and the saturation moment per Tb is 8.95 ± 0.05 Bohr magnetons which is essentially equal to the ordered moment of the free Tb^3 + ion. This ordered structure is identical to the commensurable magnetic structure of TbAu₂ at temperatures below 42.5°K, but the incommensurable transverse‐wavelike spin alignment of TbAu₂ found in the 42.5°–55°K range was not detectable in TbAg₂. Also, no detectable moment is observed for Ag in TbAg₂.