Impact of Rare-earth site Substitution on the Structural, Magnetic and Thermal Properties of Ce$_{1-x}$Eu$_x$CrO$_3$ Orthochromite Solid-solutions.

The role of slight changes of the chemical composition on antiferromagnetic ordering of Cr in rare-earth orthochoromites was investigated on a series of ceramic solid-solutions Ce$_{1-x}$Eu${_x}$O$_3$ where x varied from 0 to 1. Gradual replacement of Ce with Eu reduces the cell volume and acts equivalently to applying external pressure. Full replacement of Ce by Eu, on the other hand, reduces the N\'{e}el temperature from 260 K for CeCrO$_3$ to 178 K for EuCrO$_3$ as established by magnetization, heat capacity and neutron powder diffraction measurements. High resolution x-ray powder diffraction measurements on Ce$_{1-x}$Eu${_x}$O$_3$ and neutron powder diffraction studies on CeCrO$_3$ enable to correlate the magnetic properties of the Cr magnetic subsystem with the size of the lattice and minute changes of the bonding and torsion angles within and between the CrO$_6$ octahedra. We find that the sizes and the shapes of the CrO$6$ octahedra remain essentially unchanged as the size of the rare-earth cations is reduced whereas decreasing Cr - O - Cr bonding angles and increasing inclination of neighboring octahedra enable to compensate for the decreasing lattice size.