Valence Instability in Eu(Pd1−xAux)2Si2: The Global Phase Diagram

Abstract

A system has been discovered in which the characteristic energies of a valence instability and a magnetic ordering instability can be brought into parity. This leads to a novel phase diagram where a line of second-order magnetic transitions terminates at a line of first-order valence transitions which, in turn, terminates at a critical point. Microscopic Mössbauer-effect measurements of the order parameters across both magnetic and valence instabilities, along with bulk magnetic susceptibility measurements, are presented.