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Ferromagnetic Quantum Critical Point in the Heavy-Fermion Metal YbNi4(P1−xAsx)2

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Science  22 Feb 2013:
Vol. 339, Issue 6122, pp. 933-936
DOI: 10.1126/science.1230583

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Arsenic Makes a Difference

A quantum critical point (QCP) occurs when quantum fluctuations, which do not go away even at absolute zero, cause a gradual (so-called second order) phase change. QCPs have been observed in ferromagnets, but for ferromagnetic metals, the evidence is less clear-cut and it is thought that, as the temperature is lowered, another order—such as superconductivity—will prevent the formation of a QCP. However, Steppke et al. (p. 933), using specific heat and magnetic susceptibility measurements, found strong evidence for a QCP in a quasi–one-dimensional heavy fermion material, YbNi4(P1−xAsx)2, near an Arsenic substitution level of about 10%. The results present a challenge to theories about quantum criticality in ferromagnets.