Magnetic Structure of HoAu2

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Abstract
Neutron‐powder diffraction measurements reveal that HoAu2 (the tetragonal body‐centered CaC2‐type structure) becomes an antiferromagnet below TN(α) = 9.2°K with the onset of an incommensurate moment alignment (α) having a transverse wave modulation. The α magnetization wave with the wavelength, 6.373 Å = 1.229 a, propagates along the a axis and is polarized approximately in the direction of the b axis, all in the face‐centered lattice description. At TN(β) = 7.8°K, a commensurate transverse magnetization wave (β) starts to grow. The β wave with the wavelength equal to the a spacing propagates along the a or b axis and is polarized in the direction of the c axis. The composite configuration of the α and β transverse waves may be described as an antiferromagnetic triangular‐fan structure. In cooling, the α wave amplitude reaches rapidly to a maximum value of 6.7 μB at 6.3°K, then decreases monotonically, and diminishes near 0°K. The β wave moment follows the Brillouin curve and approaches 6.4 μB at 0°K. The composite ordered moment rises to a maximum value of 7.8 μB at around 5.5°K and declines toward 6.4 μB at 0°K. These moment values which are considerably smaller than 10 μB of the free Ho3+ ion indicate a strong crystal field effect. The phenomenum that the maximum composite moment occurs near the midpoint of the ordered phase is due likely to a strongly anisotropic, competing interaction between the RKKY exchange coupling and the crystal field effect.

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