Freezing of octahedral tilts below the Curie temperature in SrRu1-vO3 perovskites -: art. no. 104411

The crystal structure and magnetic properties of SrRu1-vO3 samples annealed in air (v=0) and high oxygen pressure (v=0.02 and 0.09) were studied as a function of temperature between 10 K and room temperature. Neutron powder diffraction analysis revealed that below T-C=163 K the b and c lattice parameters and the unit cell volume are virtually temperature independent for the stoichiometric material whereas this behavior is less pronounced in the Ru-deficient samples with decreased T-C=135 K and 82 K. We show that this previously reported Invar effect below the ferromagnetic ordering temperature originates from freezing of the octahedral tilting about the [001] axis that can be observed for both stoichiometric and Ru-deficient samples. Spontaneous magnetostriction has the largest effect on the b axis of the orthorhombic Pbnm crystal structure.