Detailed measurements of magnetization and ac susceptibility at low temperatures of 1% Zr-substituted Y9Co7 are presented. All results are indicative of itinerant weak ferromagnetism withTc ∼ 9.5 K. The zero-field magnetizations followT2 orT4/3 behaviour as in the Ni-substituted system. The estimated critical exponents areβ=0.38±0.03,γ=1.16±0.05. It is argued that the main effect of the non-magnetic Zr-substitution in Y9Co7 is to stabilize the ferromagnetic ordering by suppressing the ‘hopping’ of Co atoms along thec-axis sites of the hexagonal structure.
