Low temperature magnetic hardness in substituted SmCo5

The mechanism of magnetization at liquid He temperatures is investigated in alloys based on SmCo5 with partial substitution for Co by Ni, Ag, Al and Si. Further materials Y00.167Co0.683Al0.15 and Gd0.167Co0.683Al1.15 are included. Only homogeneous specimens of CaCu5 type are studied. Al and Si substituted materials when obtained by quenching from the melt exhibit stacking fault structures in the basal plane. These materials show, at 4.20K, outstanding coercive forces in bulk and powder form (with extrapolated values of about 60 kOe at the phase boundary Sm0.167 Co0.608Al0.255). When bulk alloys are annealed (7000C) demagnetization takes place spontaneously at critical fields with a slope comparable to the demagnetization factor rather than with the considerably smaller slope found in materials prepared by quenching from the melt. Ni and Ag substituted SmCo5, as well as Y0.167 Co0.683Al0.15 and Gd0.167Co0.683Al0.15 show no appreciable coercive forces at 4.20K. Results are discussed in terms of a model of homogeneous pinning of domain walls of atomic dimensions on the crystal lattice. The role of substituent and rare earth in establishing highly energetic domain walls is discussed. (auth)