Stabilization of collinear ferromagnetic order in Ir-doped triple-layer ruthenate Sr4 Ru3 O10

The triple-layer Sr4Ru3O10 is a spin-orbit-coupled metal featuring an intriguing combination of ferromagnetic and metamagnetic states. Here we report a comprehensive study of single-crystal neutron and x-ray diffraction on Sr4Ru3O10 with 4% iridium doping. The system crystallizes in an orthorhombic Bbem structure in which two triple layers are related by a base centering symmetry operation within one unit cell. The 4% Ir doping at the Ru site sensitively alters the structural balance between the RuO6 layers, as such the two outer-layer octahedra rotate 6.7∘ about the c axis, while the central-layer one rotates in the opposite direction by 11.0∘. The increased lattice distortion stabilizes a collinear ferromagnetic state with magnetic moments fully aligned along the c axis. The emerging perpendicular magnetic anisotropy naturally increases the critical field for the inplane metamagnetic transition to 4.5 Tesla. All results highlight the critical linkage between the magnetic properties and underlying lattice through orbital degrees of freedom, as well as the enhanced spin orbit coupling due to heavier 5d ions. Our observation provides a viable route for an efficient manipulation of the magnetic states with functionalities.