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The delicate balance between spin-orbit coupling, Coulomb repulsion andcrystalline electric field interactions observed in Ir-based oxides is usuallymanifested as exotic magnetic behavior. Here we investigate the evolution ofthe exchange coupling between Co and Ir for partial La substitution by Ca inLa$_{2}$CoIrO$_6$. A great advantage of the use of Ca$^{2+}$ as replacement forLa$^{3+}$ is the similarity of its ionic radii. Thus, the observed magneticchanges can more easily be associated to electronic variations. A thoroughinvestigation of the structural, electronic and magnetic properties of theLa$_{2-x}$Ca$_{x}$CoIrO$_6$ system was carried out by means of synchrotronx-ray powder diffraction, muon spin rotation and relaxation ($\mu$SR), AC andDC magnetization, XAS, XMCD, Raman spectroscopy, electrical resistivity anddielectric permittivity. Our XAS results show that up to 25% of Ca substitutionat the La site results in the emergence of Co$^{3+}$, possibly in high spinstate, while the introduction of larger amount of Ca leads to the increase ofIr valence. The competing magnetic interactions resulting from the mixedvalences lead to a coexistence of a magnetically ordered and an emerging spinglass (SG) state for the doped samples. Our $\mu$SR results indicate that forLa$_{2}$CoIrO$_6$ a nearly constant fraction of a paramagnetic (PM) phasepersists down to low temperature, possibly related to the presence of a smallamount of Ir$^{3+}$ and to the anti-site disorder at Co/Ir sites. For the dopedcompounds the PM phase freezes below 30 K, but there is still some dynamicsassociated with the SG. The dielectric data obtained for the parent compoundand the one with 25% of Ca-doping indicate a possible magnetodielectric effect,which is discussed in terms of the electron hopping between the TM ions, theanti-site disorder and the distorted crystalline structure.

The effect of structural and magnetic disorder on the 3$d$-5$d$ exchange interactions of La$_{2-x}$Ca$_{x}$CoIrO$_{6}$