MAGNETIC STRUCTURES OF DYAU2 AND DYAG2

Neutron-powder-diSraction study has shown that, upon cooling, DyAu 2 (tetragonal, isostructural to MnAu2) exhibits the onset of antiferromagnetism at TN(α) =33.8°K and a first-order-like magnetic transition at TN(β) =25.5°K. The moment alignment between TN(α) and TN(α) is represented by a static linear-transverse spin wave propagating along the a axis (the face-centered description) and polarized in the direction of the c axis. The wavelength of this modulation wave is 1.21 times (the a spacing), being incommensurable with the chemical repetition. At TN(β), the modulation wavelength becomes abruptly equal to the a spacing with a discontinuous increase in the rms ordered moment but without change in the moment direction. This commensurated magnetic structure persists down to 1.7°K and the saturation ordered moment is 9.2 μB. The DyAg2 structure is analogous to DyAu2 and characterized by TN(α) = 15.0°K; the incommensurate moment wavelength, 1.17α; 7N(β) =9.5°K; and the saturation ordered moment, 7.4 μB, being much smaller than 10.0 μB of the free Dy 3+ ion. The crystallographic data at 300-5°K are also presented.