Anisotropy constants of RCo5compounds

Using the singular point detection technique, we have determined the anisotropy field HA= 2(K1+2K2)/Msfor polycrystalline samples of YCo5,CeCO5,PrCo5and ThCo52. Measurements have been made in pulsed magnetic fields up to 200 kOe and over the tamperature range 4.2K-330K. In addition, magnetisation measurements have been carried out on aligned powder samples to enable independent estimates of K1and K2to be made. In the case of YCo5, a broad spectrum of anisotropy fields is apparent with a well defined satellite in some cases, which probably corresponds to the stoichiometric composition. For ThCo5,K2changes sign at about 100K. For PrCo5, the anisotropy field measured here does not agree with the low field anisotropy constants previously reported. This apparent field dependence of anisotropy constants may be due to non-collinear sublattice magnetisation.