A systematic study of the effect of substitution of Cu in MM[Co
1-xCu
x]
5 
and Fe in[MM Co
1-xFe
x]
5 
were made. The Cu substitution for Co gives stable CaCu
5type phase in the entire composition range. The lattice parameters

and

of the 1:5 phase increase linearly with increasing Cu content. Fe has only a limited solid solubility in the 1:5 phase. For MM[Co
1-xCu
x]
5alloys the

decreased from 95 e.m.u. g
-1at

to about 3 e.m.u. g
-1at

while for MM[Co
1-xFe
x]
5alloys it increased to 101 e.m.u. g
-1at

. A detailed phase composition of the alloys at 900°C and 700°C and the effect of Cu on the T
cof the 1:5 phase are also reported.