Successive magnetic phase transitions with magnetoelastic and magnetodielectric coupling in the ordered triple perovskite Sr$_3$CaRu$_2$O$_9$

We report a comprehensive temperature-dependent investigation of the 1:2 ordered triple perovskite system Sr$_3$CaRu$_2$O$_9$. It crystallizes in the monoclinic structure with space group $P21/c$, consisting of corner-sharing CaO$_6$ and RuO$_6$ octahedra. Using DC magnetization and neutron diffraction measurements, we show that this system undergoes successive magnetic transitions ~190 K and ~160 K. From the analysis of the temperature-dependent neutron diffraction and dielectric data, we demonstrate two distinguishing features of the Sr$_3$CaRu$_2$O$_9$ system: (i) magnetoelastic coupling associated with the two magnetic transitions, as revealed by a change in the unit cell volume, direct Ru-Ru distance, and bond angles and (ii) magnetodielectric coupling, as revealed by the anomalies across the two magnetic transitions. The present results would add significantly to the current understanding of the triple perovskites with incipient spin-orbit coupling.