The magnetic anisotropy constants K1, K2 and K4 have been measured for the uniaxial easy basal plane ferrimagnetic compounds Ho2Fe17 and Ho2Co17 at a temperature of 4.2 K, using vibrating sample magnetometers. The observed anisotropy constants K1 and K4 for both compounds are about an order of magnitude smaller than K1 and K4 predicted from an analysis of spin wave data.
Clausen, K. N., & Nielsen, O. V. (1981). Magnetic Anisotropy in Single Crystals of Ho2CO17 and Ho2Fe17. Journal of Magnetism and Magnetic Materials, 23(3), 237-240. https://doi.org/10.1016/0304-8853(81)90041-X