Abstract
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 T-MI = 357 K, which is well separated from antiferromagnetic order at T-N = 110 K. Substitution of a 5d element, Ir, for Ru enhances spin-orbit coupling and locking between the structural distortions and magnetic moment canting. Ir doping intensifies the distortion or rotation of Ru/IrO6 octahedra and induces weak ferromagnetic behavior along the c axis. In particular, Ir doping suppresses TN but concurrently causes an additional magnetic ordering T-N2 at a higher temperature up to 210 K for 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.
