  We report structural, magnetic, transport and thermal properties of
single-crystal Ca2Ru1-xIrxO4 (0 < x< 0.65). Ca2RuO4 is a structurally-driven
Mott insulator with a metal-insulator transition at TMI = 357 K, which is well
separated from antiferromagnetic order at TN = 110 K. Substitution of 5d
element, Ir, for Ru enhances spin-orbit coupling (SOC) and locking between the
structural distortions and magnetic moment canting. In particular, Ir doping
intensifies the distortion or rotation of Ru/IrO6 octahedra and induces weak
ferromagnetic behavior along the c-axis. Moreover, the magnetic ordering
temperature TN increases from 110 K at x = 0 to 215 K with enhanced magnetic
anisotropy at x = 0.65. The effect of Ir doping sharply contrasts with that of
3d-element doping such as Cr, Mn and Fe, which suppresses TN and induces
unusual negative volume thermal expansion. The stark difference between 3d- and
5d-element doping underlines a strong magnetoelastic coupling inherent in the
Ir-rich oxides.
