We studied the crystal and magnetic structure of ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ as function of pressure with different diffraction techniques. The first-order phase transition observed at a moderate pressure of $P=0.5\mathrm{GPa}$ between the insulating and the metallic high-pressure phase is characterized by a broad region of phase coexistence. The following structural changes are observed as function of pressure: (a) A discontinuous change of both the tilt and rotational angle of the ${\mathrm{RuO}}_6$-octahedra at this transition, (b) a gradual decrease of the tilt angle in the high-pressure phase $(P>0.5\mathrm{GPa})$, and (c) the disappearance of the tilt above 5.5 GPa leading to a higher symmetry structure. The magnetism was studied by single-crystal neutron diffraction: The ferromagnetic component of the high-pressure phase and a rearrangement of antiferromagnetic order in the low-pressure phase have been observed.

• Received 14 February 2005

DOI:https://doi.org/10.1103/PhysRevB.72.094104