Magnetoelastic coupling in RTiO3 (R=La,Nd,Sm,Gd,Y) investigated with diffraction techniques and thermal expansion measurements

Abstract

A detailed analysis of the crystal structure in $R\mathrm{Ti}{\mathrm{O}}_3$ with $R=\mathrm{La}$, Nd, Sm, Gd, and Y reveals an intrinsic coupling between orbital degrees of freedom and the lattice which cannot be fully attributed to the structural deformation arising from bond-length mismatch. The $\mathrm{Ti}{\mathrm{O}}_6$ octahedra in this series are all irregular with the shape of the distortion depending on the rare-earth ionic radius. These octahedron distortions vary more strongly with temperature than the tilt and rotation angles. Around the Ti magnetic ordering all compounds exhibit strong anomalies in the thermal-expansion coefficients, these anomalies exhibiting opposite signs for antiferromagnetic and ferromagnetic compounds. Furthermore, the strongest effects are observed in materials close to the magnetic crossover from antiferromagnetic to ferromagnetic order.