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Evidence of ferromagnetic quantum phase transition in Ba$_{1-x}$Sr$_x$VS$_3$

Resistivity under pressure and magnetization measurements on Ba$_{1-x}$Sr$_x$VS$_3$ single crystals with 0 $\leq x \leq$ 0.18 and no sulphur deficiency show an abrupt onset of ferromagnetic (FM) order at a critical value $x$=0.07, concomitant to a change of the magnetic properties at the metal-insulator transition (MIT) and to a collapse of the unit cell at ambient temperature. A reduction of the MIT temperature to 50 K upon $x$ that scales as the V-S distance is also observed. This gives evidence of a chemical pressure induced quantum phase transition that stabilizes the incipient FM order of BaVS$_3$. The $0.07<x$ results suggest a coexistence of FM and metallic phases at larger $x$.