MAGNETIC STRUCTURES OF TBAU

Neutron-powder-diffraction study has shown that, in the range 55°-42.5°K, TbAu2 (tetragonal, isostructural to MnAus) exhibits a linear-transverse-wave spin alignment propagating along the a axis (the face-centered description) and polarized in the c axis direction. The wavelength of this static magnetization wave is incommensurable with the atomic repetition and varies 1.200-1.186 in a spacing units in the range 55°-42.5°K. The rms moment per Tb at 42.6°K is 5.1 Bohr magnetons. At just below 42.5°K, a first-order magnetic transition takes place and the wavelength of the transverse wave abruptly becomes equal to the a spacing. The resulting antiferromagnetic structure persists down to 2°K and the saturation moment is practically identical to the ordered moment of the free Tb3+ ion, 9.0 Bohr magnetons. The crystallographic data in the range 300°-5°K are also presented.