  We present a study of the magnetic properties of Zr1-xNbxZn2, using an Arrott
plot analysis of the magnetization. The Curie temperature TC is suppressed to
zero temperature for Nb concentration xC=0.083+/-0.002, while the spontaneous
moment vanishes linearly with TC as predicted by the Stoner theory. The initial
susceptibility chi displays critical behavior for x<=xC, with a critical
exponent which smoothly crosses over from the mean field to the quantum
critical value. For high temperatures and x<=xC and for low temperatures and
x>=xC we find that chi^(-1)=chi_o^(-1)+aT^(4/3), where chi_o^(-1) vanishes as x
approaches xC. The resulting magnetic phase diagram shows that the quantum
critical behavior extends over the widest range of temperatures for x=xC, and
demonstrates how a finite transition temperature ferromagnet is transformed
into a paramagnet, via a quantum critical point.
