The magnetic anisotropy of YCo4B determined by the singular point detection (SPD) method and
magnetization measurements over a large range of temperature is reported. The anisotropy energy of CeCo4
B estimated by magnetization measurements is one order of magnitude larger than those of compounds with
Y, La, or Gd. The temperature dependence of anisotropy energy in YCo4B is discussed in the light of the
temperature variation of the c/a ratio and the giant anisotropy of CeCo4B is presumed to be due to the
itinerant character of the 4f states in the compound.
