Critical Phenomena and the Quantum Critical Point of Ferromagnetic Zr1-xNbxZn2

TL;DR

This study investigates the magnetic quantum critical point in Zr1-xNbxZn2, revealing how ferromagnetism vanishes at a critical Nb concentration and demonstrating the crossover from classical to quantum critical behavior.

Contribution

It provides experimental evidence of quantum criticality in Zr1-xNbxZn2 and characterizes the critical behavior of susceptibility near the quantum critical point.

Findings

Curie temperature suppressed to zero at x=0.083

Susceptibility exhibits critical behavior crossing from mean field to quantum critical exponents

Quantum critical behavior extends over a wide temperature range at the critical concentration

Abstract

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.