Critical phenomena and the quantum critical point of ferromagnetic Zr1-xNbxZn2

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 χ 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 χ-1=χ0-1+aT4/3, where χ0-1 vanishes as x→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.