Tuning the critical magnetic field of the triplon Bose-Einstein condensation in Ba${}_{3-x}$Sr${}_x$Cr${}_2$O${}_8$

The structure and magnetic interactions of the triplon Bose-Einstein condensation candidates Ba${}_3$Cr${}_2$O${}_8$ and Sr${}_3$Cr${}_2$O${}_8$ have been studied thoroughly in the literature, but little is known about a possible triplon condensation in the corresponding solid solution Ba${}_{3-x}$Sr${}_x$Cr${}_2$O${}_8$. We have prepared various members of this solid solution and systematically examined their magnetic properties in high magnetic fields up to 60 T and at low temperatures down to 340 mK, by means of pulsed field and cantilever magnetometry. From these experiments for $x\in \{3,2.9,2.8,2.7,2.6,2.5\}$, we find that the critical fields of Ba${}_{3-x}$Sr${}_x$Cr${}_2$O${}_8$ decrease monotonically as a function of the Sr content $x$. This change is in good agreement with the earlier reported variation of the magnetic interactions in these compounds.