Ferromagnetic quantum critical point induced by dimer-breaking in SrCo2(Ge1-xPx)2

In contrast to classical phase transitions driven by temperature, a quantum critical point (QCP) defines a transition at zero temperature that is driven by non-thermal parameters(1-3). In the known quantum critical d-electron systems, tuning the electronic bandwidth by means of changing the applied pressure or unit-cell dimensions, or tuning the d-state population, is used to drive the criticality(4-6). Here we describe how a novel chemical parameter, the breaking of bonds in Ge-Ge dimers that occurs within the intermetallic framework in SrCo2(Ge1-xPx)(2), results in the appearance of a ferromagnetic (FM) QCP. Although both SrCo2P2 and SrCo2Ge2 are paramagnetic, weak itinerant ferromagnetism unexpectedly develops during the course of the dimer breaking, and a QCP is observed at the onset of the FM phase. The use of chemical bond breaking as a tuning parameter to induce QCP opens an avenue for designing and studying novel magnetic materials.