  We have investigated the in-plane uniaxial pressure effect on the
antiferromagnetic Mott insulator Ca2RuO4 from resistivity and magnetization
measurements. We succeeded in inducing the ferromagnetic metallic phase at
lower critical pressure than by hydrostatic pressure, indicating that the
flattening distortion of the RuO6 octahedra is more easily released under
in-plane uniaxial pressure. We also found a striking in-plane anisotropy in the
pressure responses of various magnetic phases: Although the magnetization
increases monotonically with pressure diagonal to the orthorhombic principal
axes, the magnetization exhibits peculiar dependence on pressure along the
in-plane orthorhombic principal axes. This peculiar dependence can be explained
by a qualitative difference between the uniaxial pressure effects along the
orthorhombic a and b axes, as well as by the presence of twin domain
structures.
