Magnetic Structure of ErAg2

A neutron powder diffraction study has been made of the magnetic properties of ErAg₂ (the tetragonal body‐centered CaC₂‐type structure) at temperatures between 297 and 1.5°K. At 5.2°K, the onset of an incommensurate, sinusoidal moment alignment takes place (the α structure). The α magnetization wave propagates along the a axis and the α wavelength is $\text{6.345\hspace{0.17em}Å\hspace{0.17em}=1.277 a}$ , all in the face‐centered lattice description. The x(∥ a) and y(∥ b) components of the α wave amplitude are approximately equal, while the z component is essentially zero. At 3.5°K a commensurate magnetization wave starts to grow (the β structure). The β wave propagates also along the a axis and the β wavelength is equal to the a spacing. In further cooling below 3.5°K, the x component of the α amplitude decreases rapidly and diminishes completely below 1.5°K, while the y component retains its 3.5°K value down to 1.5°K. The maximum x component of the α amplitude is 5.3 μ_B at 3.5°K and the maximum y component takes the same value at 3.5–1.5°K. No significant variation was observed on the α wavelength at $\text{4.8>T>1.5°}\mathrm{K}$ . Regarding the β moment, the x component is predominantly larger than the y component and the z component is undetectably small. The β moment components follow the Brillouin‐type magnetization and the moment values extrapolated to 0°K are approximately 6 and 3 μ_B for the x and y components, respectively. The composite configuration of the α and β waves portrays an antiferromagnetic stacking of the distorted fan‐type moment arrays.